Updated 22 July 1997
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Rewiring Vixens and other older
TVRs
Why
rewire?
Low charging currents | Non-flashing indicators |
Rewiring
strategies
The plan
Implementation
Implementation
Electronic indicators | Hazard lights | Anti-theft precautions | Switch to negative earth wiring |
Summary
Legal bits
Legal bits
One of the many challenges facing the owner of an older TVR is the electrical wiring system. It is the frequent source of many intermittent problems and in some cases, can lead to worse catastrophes such as setting the car alight. This nearly happened with my first TVR, an S1 Vixen. This article describes some of the electrical problems that can be caused by poor connections and how to solve them. In some cases, the only solution is to rewire but in many instances, simple repairs are all that are required. The examples are based on my experiences from the re-wiring the Vixen, but the principles and techniques are applicable to almost any TVR.
Why rewire?
There are several reasons, or to be accurate, problems that warrant rewiring. The first and most important is to replace wiring where the insulation is no longer effective. On older TVRs, the insulation used was rubber and this perishes with age. As a result, there is a potential problem if two wires short out and can cause a local electrical fault which leads to the loom smoking and bursting into flame. This happened on my S1 Vixen one day when I noticed that turning off the ignition did not stop the engine. Moments later, smoke started to appear from under the bonnet. Fortunately, I was quite lucky in that I had fitted wing nut connections to the battery connection and managed to disconnect the battery before the smoke turned into a fire. Despite this, the wiring loom was a charred mess which obviously needed replacing.
Cars that have rubber insulated wiring should be checked regularly to ensure that the insulation is still intact. If it is perished or cracked, then I suggest a re-wire is considered or at least get a fire extinguisher and carry it in the car...
Rewiring the Vixen identified and solved several other electrical problems that I was experiencing and with hindsight was probably something that should have been undertaken earlier. Many of the connections were corroded and contributing to the poor state of the electrical system. While bullet connectors often looked fine, trying to separate them often identified bad corrosion or wires that were just hanging on by a few threads. Needless to say, they were all replaced. There were some other specific problems that were identified during the work.
Dim headlights especially when idling
This was caused by a combination of two faults: low voltage/power from the dynamo/alternator and bad connections causing increased resistance and thus reducing the voltage actually reaching the bulb. The dynamo voltage problem is described in more detail later on. The common causes of bad connections with light fittings are due to poor earths and/or defective fittings. Let's tackle the poor earths first.
Most car fittings are designed to get their earth connection through the metal bodywork which of course a TVR does not have. As a result, the earth connection has to be made by a separate lead attached to the fitting and this is often the source of the problem. This connection is often exposed to the air and corrodes. The solution is to create a new connection. If a self tapping screw is used to attach the fitting to the bodywork, use a nut and bolt behind the fixing and add a flying lead. Use a serrated washer to ensure that the nut does not come undone and provides a good electrical contact. On some light fittings there are cylindrical covers that can be used. Brighten up the metal work and use a jubilee clip to clamp the bare earth wire to the unit. Covering the clip with self-amalgamating tape will ensure that the connection will not corrode and cause problems in the future. The clip is the easiest way of making contact; my experience has been that while the metal may look like it can be soldered, in practice it cannot be successfully be done.
The connection to the bulb can also cause a problem. It often consists of a spring loaded connection that is directly attached to the power wire. This consists of a contact at the end of the wire which goes through an insulating washer and a spring. The spring ensures that good contact is maintained. This arrangement can seize up and the contact and bulb are thus prevented from meeting or the contact itself can be corroded. It may require cleaning or in some cases, replacing. The Vixen had a couple of these that needed repairing. This was done by soldering a lump of solder to the end of the near wire to create the contact. The lump was filed flat to create a clean and level surface for the bulb. It was then passed through a washer made from polystyrene sheet (available in different thicknesses from most model shops) and a replacement spring taken from an old biro. This was then fed into the holder and the wire taken out the back (see figure 1).
Figure 1: Repairing a bulb holder
Low output from the dynamo
This can be caused by worn brushes within the dynamo or a badly adjusted control box. The symptoms of worn brushes are reduced power from the dynamo and insufficient current to meet the loading. If the car is fitted with a current meter as part of its instrumentation, this can easily be recognised as a current drain from the battery with the headlights and so on switched off. With a voltage meter, this can be a little harder to see but usually shows itself as a lower from normal voltage. Replacing the brushes is normally straightforward or the dynamo could be exchanged for a new or re-conditioned one. One small point: the early Vixens used a mixture of either long or short case dynamos. The length difference is about one to two inches. Long case dynamos are less common than the short case versions and therefore replacements can be harder to fit. The short case dynamo does the same job but unfortunately does not fit the mounting bracket. The choice is to either modify the bracket or go to a scrapyard and get one. This does turn a "I'll just change the dynamo job" from a small one hour task to one that takes all day! If you get a bracket from a scrapyard, take the bolts as well &emdash; they are also very hard to get.
The control box usually consists of two relays that regulate the output voltage and current that the dynamo produces. The voltage relay is normally closed when the dynamo output voltage is below a pre-set value (about 14 volts) and this feeds power into the outer coil of the dynamo. This then causes the dynamo to output electrical power. As the output voltage from the dynamo rises and nears the pre-set value, the relay starts to energise, its contacts break apart and will disconnect the power to the coil. The output voltage then falls, the relay contacts will make again and restore the power. This operation repeats many times a second and the end result is an average voltage from the dynamo. The value of this voltage is determined by the make/break point of the contacts. This can be mechanical adjusted to raise or lower the voltage. The current relay works in a similar way but measures the output current.
If they are out of adjustment, the dynamo will produce insufficient power to maintain the battery charge or drive lights and accessories when idling. Any additional resistance in the circuits due to poor connections will make this problem worse. The main adjustments are the mechanical setting of the relay gaps and the measured voltage from the dynamo for a given engine RPM. The method for adjustment is simple but does vary from car model to car model. It is usually described in the appropriate service manual for the mainstream car that provides the engine for the TVR. For a Vixen, this information would be in a Mk II Cortina workshop handbook and so on. With the Vixen, I could not get the controller to adjust correctly and the only recourse was to replace it. However, it still needed some adjustment to get the absolute best out of it i.e. every last microamp of current that I could!
Low charging currents
The dynamo faults that can cause this have already been covered but there are a couple of others things to check. Ensure that the battery is in good condition and has electrolyte in every cell. Make sure that the battery connections are also good. Covering them in petroleum jelly is a good way on ensuring that good connections stay that way.
Non-flashing indicators
This was caused by insufficient current consumption by the indicator circuit. The flasher unit on the older cars used a bi-metal strip which was part of the electrical circuit. When a current flows through it, its resistance cause its to heat up and the strip bends. This will eventually break the contact, the current will stop flowing and the strip will cool down. When it cools it reverts to its original shape and re-establishes the electrical contact. This continual make and break operation flashes the indicators. If there is insufficient current caused by low voltage and/or poor connections, then the current and the heating effect is reduced so that the strip takes longer to move and break the contact. In some cases, it may never do this and the indicators can stay on permanently.
Just because your indicators stay permanently on does not mean that the wiring is at fault: the contacts within the flasher unit can stick and sometime physically knocking the unit will start it operating again. If the problem persists with a replacement unit, then the fault will often lie with one or more of the faults previously described. Another possible cause is the fitting of a lower wattage bulb that normal e.g. a five watt bulb instead of a 10 or 21 watt one. This reduces the current consumption and can cause the same symptoms.
Rewiring strategies
If it is necessary to rewire your pride and joy, and you want to do it yourself, then it is not too daunting a job for TVRs that do not have engine management systems. It does require some careful planning and approach to ensure not only everything works probably but that it is correctly fitted. With post M series cars with engine management and so on, the task of re-wiring is just more complex, takes longer and has many more things to go wrong and this may be a good reason for getting someone else to do it! On the other hand, the connections and insulation are often more reliable and thus the need for a complete re-wire is less frequent. With these models, keeping the connections clean and good is the main point. However for those brave enough to try, the techniques are still applicable.
What size wire?
It is important that the correct size of wire is used. Normally three sizes are used which can carry different currents. Connections from the starter motor to its solenoid require very heavy cable to cope with the several hundred ampere currents that are involved. The cables between the dynamo, its controller box and the fuse box must take several tens of amperes and most other connections require cables that can cope with probably ten amps. The current can be worked out by dividing the power in watts by 12 to give the average current. A 55 watt headlamp bulb will take about 4.5 amps. A 21 watt brake light will use just under 2 amps. These figures are averages and far higher currents flow when lights are first switched on. The key message is to use the right size wire for the job. If in doubt use a heavier cable. The current consumption needed by the various electrical items can be obtained from a workshop manual(s) for a similar car. For a Vixen, the Mk II Cortina manual is an ideal choice. I used manuals for Minis, MG Midgets, MGBs, TR4/5/6 as well and between them they covered virtually every bit of electrical gear that the Vixen had.
How many wires?
Most wiring looms use a single wire between the various connections. However for very reliable systems, it is better to use more than one. The cost of the extra wire is not that great and the added reliability is worth while. As a result, the Vixen got two wires when ever possible between items. This means that a corroded connection would not cause a failure and the current capacity would be twice that of a single wire and provide an extra margin of safety. Each wire would be the appropriate size to carry the required current on its own. In addition, spare wires would be added just in case.
I was told once that Formula One cars take this process a step further and use THREE wires per connection. So if you want a Formula One spec TVR you know what to do!
Making earth connections
The original wiring loom contains both earth and live cables and if these short out, they can cause a fire problem. It is safer therefore to route the earth connections separately and to do this, several earthing points were made on the chassis so that earth wires did not have to passed from the bonnet or dashboard to the rear lights and so on. This was done to simplify things and reduce the amount of wiring that went through the car. I must admit that the safety advantages were an afterthought!
The earth connections were made by drilling a hole into the chassis tubing and using a self tapping to attach a connection. This is fine for inside the car or where the chassis is not exposed to the elements but it does break the integrity of the tubing and could potentially introduce corrosion. An alternative is to use the jubilee clip technique and clamp the earth wire to a bare part of the metal tube. The clip and connection can be painted over or wrapped with tape if necessary.
Separating the loom
The loom was split into several parts so that it could be built and tested individually. The dashboard was chosen as the central point and looms distributed to the front lights, rear lights, the ignition and dynamo system and to the interior accessories. The looms were connected using bullet connectors initially but since then high current connectors for electrical and electronic equipment have become available and these would be an ideal alternative (figure 2).
Figure 2 : The loom
The plan
The first thing to do is to plan how the rewiring is going to be done.
- List all the electrical items and their current
capacity.
Make sure you don't forget those odd little items such as the temperature and fuel tank sender, fuel pump and so on.
- Define where the looms are going to go.
Use string to get some idea of how much cable will be needed. Add a foot to each measurement so that if a connection goes wrong there is some spare cable available to remake the connection.
- Work out how each component is wired
This is easy for lights but is not straightforward for instruments and the ignitions system. I found looking at wiring diagrams from normal car manuals and checking the Vixen's wiring gave a good insight into how they were connected.
- Draw out the wiring diagram
I had intended to do this for future reference but didn't. Instead, I used the tried and tested approach of scraps of paper, cardboard and anything else that was around. I got away with it but it's better to do it properly.
- Buy lots of connectors, wire and a good multimeter.
You will also need a crimping tool, a soldering iron (25
watts is ideal).
Several times I thought I had enough only to find that I had run out. Maplins sell automotive connectors in bulk and at a very good price.
To ensure a good contact, I soldered every connection as well as crimping it. A small mole grip or vice is very useful to hold the connector while soldering &emdash; they tend to get too hot to hold!
Implementation
The next step is where the real fun starts...
- Remove the dashboard and rewire the instrumentation
and switchgear. The connections to the other parts should
be labelled and gathered together, ready for integration
with the other parts of the loom.
This makes life a lot easier and allows the circuitry to be tested in the comfort of a warm kitchen.
- Make the sub looms using the string lengths as a
template.
Initially, I planned to do this inside but got nervous about the accuracy of the measurements and did it in situ on the car. The longest connection was installed and the other cables added till the loom was complete. The connections to the lights and so were then made and the loom wiring finally wrapped using insulating tape. Where a flat loom was needed, the wires were laid side by side on a piece of gaffer tape. A second piece was then placed over the top and the edges trimmed. This was used to route the cables to the rear lights, over the transmission tunnel and underneath the carpeting. The original wiring path was under the transmission tunnel.
- Test the systems step by step.
A small battery can provide a small voltage instead of connecting the car battery and a voltmeter to test that the power reaches the connections correctly, before connecting the lights and so on. An alternative is to use the continuity setting on a multimeter or an ohmmeter. The audible ones are great and mean that you do not have to actually see the meter. This is useful when upside down and with your head in a footwell. I greatly extended the test leads so that I could have one test probe at one each end of the car. Check and double check and try and be patient. Remember that connecting out a power wire to earth by mistake has the same result as a short: lots of smoke and flames! Make sure that this is not done before connecting the car battery.
- Connect the battery and try out the various
systems.
Start with the lights and gradually work through the system. If the testing was good, then everything should work.
- Fix the loom in place with cable ties and/or
tape.
Keep it away from exhausts and other hot places.
Special requirements
Some electrical items were not as straight forward as could be imagined.
Tacho
The tacho connection is a little strange and may consist of a simple loop of wire from the ignition switch to the coil. The current impulses that flow through the wire and the loop are detected internally by the tacho and counted to work out the rpm for the needle to display. To do this, the tacho is usually marked with the number of cylinders that it thinks the engine has and this must match the actual value to ensure an accurate reading. If you have added an electronic ignition system or thinking of doing so &emdash; a worthwhile addition in my experience &emdash; then the electronics may not generate the current impulses in the same way and thus cannot drive this type of tacho. Either the tacho must be replaced with a different model or a special impulse tacho unit must be added or included with the electronic ignition system. Check this point before parting with any cash.
Fuses
Rewiring is an ideal opportunity to upgrade the number of fuses that were commonly used from two to more and thus allow the various electrical components to be separately fused. More sophisticated fuse boxes can be obtained from the breakers yard or from Maplins. You can also move the box from under the bonnet to somewhere more accessible. I moved mine to behind the glove box. I also used the unconnected fuse sockets as holders for some spares.
Again it is important to ensure that the right size fuse is used and this is easily found out from the wiring current calculations.
Replacement switches
With modern cars, switches do not switch the power directly to the electrical accessory but instead power a relay that switches the current. As a result, many of the replacement switches that are available are not designed to switch these heavy currents and at best can go open circuit or at worst melt. Ensure that any replacement switch is capable of directly switching the current if the original switch worked that way. If not, then a relay must be used to isolate the switch from the heavy currents.
If you can't get replacements from David Gerald then try the MG or Jaguar spares companies. Failing that it's back to the breakers to find a donor MG, TR or Jaguar and put its switches to a far better use.
Additions
Re-wiring is an ideal opportunity to add some extras to the electrical system that can make life just that little bit easier. Here are some suggestions.
Under bonnet inspection light
Fix a light and switch at the top of the bonnet so that when it is raised, the light will illuminate the engine bay. A small interior light from an accessory shop is ideal.
Electronic indicators
The bi-metallic flasher unit can be replaced with an electronic version which flashes irrespective of the current and voltage. These are easy to make or can be obtained, usually as part of a hazard warning light kit. They normally consist of an electronic timer that pulses a relay to generate the correct on-off period. This was going to be my last resort but fortunately the re-wiring and control box adjustment solved the problem and I did not need to do it.
Hazard lights
Following on from the previous point, hazard lights can be added but this should not simply connect both sets of indicators to the same bi-metallic flasher unit as the doubled current will result in either a burnt out unit or a flashing rate that is twice that expected. A second flasher unit and/or a relay is needed to maintain the right loading.
Anti-theft precautions
Now is also an ideal time for installing or uprating the burglar alarm and fitting an electrical immobiliser. Extra sensor wires can easily be routed through along with the main wiring and it is easy to add hidden switches to isolate the fuel pump, ignition and so on.
Switch to negative earth wiring
This can be done but it is a little complicated. It does involve reversing the polarity of most of the instruments and re-renergising the dynamo. As a result, rewiring is an ideal time to do it. For more information about the process, it is described in a Practical Classics book on maintaining classic cars and has a whole chapter devoted to the subject. I must admit I wimped out and did not do it. At the time, positive earth accessories were still about. Today, this is not the case and switching the earthing polarity is the usually only way to get around the problem and allow other accessories to be fitted.
Summary
Rewiring is not as difficult a job as I first imagined and it took me three evenings and an afternoon to complete. The only thing that I got wrong was reversing the rear indicators which simply corrected by swapping the connections round at the dashboard end. After I finished it, I appreciated why looms are expensive to buy and have installed. However, the benefits were simply amazing and it must rate as one of the best things that I ever did to the car.
Legal bits
This article is copyright Steve Heath.
It may be freely distributed providing none of the content
is changed or omitted.
The opinions expressed in this article are those of the
author unless otherwise attributed. They are not and should
not be taken as the opinions of the TVR Car Club or TVR
Engineering.
Whilst the information contained in this article has been
carefully checked for accuracy, neither the author, the TVR
Car Club nor TVR Engineering assume any responsibility or
liability for loss, damage or injury caused by any errors
in, or omissions from, the information given.
As technical characteristics are subject to rapid change,
the data contained are presented for guidance and education
only. For exact detail, consult the relevant standard or
manufacturers' data and specifications.
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