Lotus Elan

Lotus Electrics

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So you have some electrical problems that you can't put your finger on.

There is a range of options from repair through, complete replacement to a system upgrade and it depends on your time and budget constraints and how poor the condition of the wiring in your car is as to what you want to do.

I will deal with those issues in a moment, but first we need to understand why we have problems, and a little about electricity.

This article is written with respect to negative earth cars. If you have a positive earth car you will have to be aware that the readings (and some actions) are different than those suggested.


What is wrong with early Lotus electrics?

There are five major problems with the electrics on the early Lotus cars, I have ranked them in the order in which I think is most important cause of problems.


The biggest problem is that they the cars are now old. All things wear out and after about 30 years the electrics have had their day. Corrosion, vibration and dirt, not to mention mechanical wear have all taken their toll. In a lot of cars the wiring is now so fragile that an attempt to mend one thing will break another.


Another problem with Lotus electrics is precisely the thing that makes the cars so good, the backbone chassis. Let me explain. Steel is not a very good conductor but in a normal car there is enough steel about to make a reasonable conductor - think of it as a fatter wire, the more metal there is the more current that the wire can reasonably carry. Because there isn't very much of the chassis it doesn't make a very good front to back conductor. This makes the electrics very sensitive to connectors and joint ageing and corrosion.


The body is glass fibre, which is a really bad conductor (an insulator). This complicates the wiring because it means that there is no easy return path for the electricity through the body. This means that all the ground connections have to be expressly wired. Lets take an example of the courtesy light.

Normally there would be a connection from the permanent live circuit (battery) to a switch that is turned on by the door opening, from this switch there would be a wire to the light. The negative side of the light would be bolted or screwed to the body, which will act as a conductor allowing the current to flow back to the battery. In a Lotus this return path has to be provided by an additional wire which will connect to a common point on the not very conductive chassis.

So the wiring appears more complicated than a normal car as there are more cables than normal.

Previous owners

For some reason electrics aren't understood. This combined with excellent performance/cost ratio of these cars seems to mean that they have often been owned by people who have no technical understanding and no qualms about doing unspeakable things to them - and normally causing more problems than they solve.


Loti have always been manufactured with cost in mind. This has two implications on the wiring.

The cheapest parts were installed, from whatever source was available so most of the cars aren't identical. There were many official and dealer options, and these don't include the self-installed options of the car's original assemblers. This means that many of the wiring looms are different.

A lot of blame is placed on the Lucas connectors and components used extensively. The connectors were designed for about a 15-year life expectancy with cost of assembly being a priority, it is no wonder that they are now causing trouble.

Tools you may need

There are some tools that you will need for any electrical work on a car.

  • General tools such as screwdrivers and spanners - for gaining access and component removal
  • Low wattage 12V light bulb with leads with crock clips on the end. This can be a useful test aid.
  • Inspection light with gas discharge bulb (lots of light and the bulbs run cold)
  • Wire cutters
  • Wire strippers
  • Pliers: a couple of sizes is good
  • Multimeter - you need resistance, voltage and possibly current ranges accuracy isn't important, but the ability to measure down to <1 ohm is good so a cheap digital meter is probably best
  • Long multimeter lead - 20 feet of GOOD wire with crock clip on one end (that will grip a car battery terminal or an engine block) and a multimeter plug on the other end (normally a 4mm jack plug). (all available from Tandy/Radio Shack etc)
  • Wire wool - for cleaning terminal, plugs etc
  • Copper grease - for protecting items from corrosion
  • Crimping tool for red, blue and yellow crimps. Practice with this first before needing to use them in anger
  • A selection of crimps, more than enough for the job to be undertaken
  • Wire of appropriate colours (if necessary)
  • Circuit diagrams. You will need at least 2 one will be you car master to mark up all those changes and non-standard features. One you will work on and with. I suggest you use a photocopier to enlarge them to increase legibility.
  • Pad of paper and some pens. (for writing notes to yourself as you go)
  • Insulating tape
  • Binding tape or spiral bind or lacing cord for making up new looms

What you need to know about electrics

Electrics are SIMPLE. They really are very SIMPLE, there is just a lot of them and this makes them look complicated. So remain calm. Remember that it is simple. There is no magic. A logical process will solve all the problems.

Have you ever untangled a ball of string? It is just like that. No amount of pulling and anger will solve the problem, but simply starting at one end and working to the other will deal with all of the knots and tangles.

So how do the electrics work? This doesn't matter all you need to know is that there has to be a connection from the positive (battery and/or generator) through the device and back to the negative (battery and/or generator). This is the same for all the electric things in the car, and I do mean all electrics for battery charging, spark plugs, rev counters etc etc etc. This continuous connection is called a circuit.

Here are a few electrical words with some explanation that will help.

  • Voltage - a measure of how hard a the electricity is pushed around a circuit or how much push it takes to get the electricity through a device. This is measured in Volts - Symbol V
  • Resistance - how hard it is to get electricity through a device. The resistance of some devices changes when they are operating. Measured in Ohms - symbol "Horse shoe open end down"
  • Current - How much electricity is being pushed through a device. Measured in Amps - Symbol A
  • Power - How much oomph is dissipated in a device. Measured in Watts - Symbol w. About 750w make 1horse power.

Some simple maths.

This is here not to confuse or upset you but to help with a few ideas, we need no numbers just a little understanding of the implications.

Voltage = Current Multiplied by Resistance


Current = Voltage divided by Resistance

So in cars voltage is almost constant so the current flowing through a device is dependent on the resistance of the device (circuit or bulb or motor or connector). The lower the resistance the more current flows.

Power = Voltage multiplied by Current


Power = Current multiplied by Current divided by Resistance

So, since voltage is almost constant, to get more power (e.g. a more powerful head light bulb) more current must flow through the circuit. For more current to flow the resistance in the circuit has to be lower.

This also means that if a headlight bulb isn't as bright as it should be there more resistance in the circuit than there should be.

Right the TWO VERY_ important bits.

  1. The voltage applied to the circuit is equal to the sum of all the voltage dissipated by all of the components in the circuit. Lets take an example you can do this if you have a reasonably good multimeter, the figures are off my car. Don't start the car, and turn on the headlights. Measure the voltage across the battery - 13.8V. This is the voltage applied to the circuit. Measure the voltage across the headlight, the actual pins of the head light (these may be warm) - 13.5V. Now take your long multimeter lead and connect it to the positive terminal of the battery and plug it into the positive terminal of the multimeter, with the negative terminal of the multimeter connect it to the positive terminal of the lights - 0.1V. Now connect the long multimeter lead to the negative terminal of the battery and the negative terminal of the multimeter and measure the voltage to the negative terminal of the light - 0.2V. As you can see not all of the voltage is dissipated over the light bulb. Some of it is dissipate on the way to the light bulb, and some on the way back to the battery.
  2. The current that flows out of the battery is the same as that which flows back in. As long as you don't have any electronics that will be upset buy this you can try it. I must admit that I haven't. Also make sure that your multimeter can measure suitable currents. Switch the side lights on (the little ones) now measure the current flowing out of the positive terminal of the battery, you will have to disconnect the battery clamp and hold the multimeter in it's place. Not shorting any of the terminals to ground. This may be more than 10A so make sure your multimeter can take it. Now measure the current flowing into the battery - remove the negative battery clamp, and connect the multimeter between this and the battery. The current will be the same. Now measure the current flowing through both side lamps and the tail lamps and this will add up to the current flowing in and out of the car battery. (The clock will also take some current etc)

Just think about these two for a moment with your circuit diagram. All the devices on your car are designed to work with 12V across them. This means that if you have a failing device and it hasn't got 12V across it them then some of that voltage is being used to push current through other parts of the circuit, parts that should be easy to push current around.

Right now you know almost all that you will ever need to know about electricity.

In situe repair

This is used if the wire is generally good and hasn't been inappropriately modified. So before we fix the problem we need to identify the real cause of the problem.

Device X doesn't work

For any electrical device to work there has to be a circuit. So if one component doesn't work it is likely that there is either a fault in that component or it's circuit. If a group of components don't work then it is likely that there is a common (or if you are really unlucky - several common reasons)

I like to start with the device, does it seem to be damaged in any way - burnt buckled or bent? For example if you are having trouble with a light it might be that the spring contacts aren't making good contact with the bulb so the problem is bent bulb contacts. Generally if the unit is broken all you can do is remove it, and repair or replace it.

If you haven't fixed it by simple inspection it's not a simple problem and some diagnosis will be needed. Next, do you know where the fuse for this device is? Is the device individually fused, if not are other things on that fuse circuit still working? If you are unsure which fuse is which take the working wiring diagram and use this to help you trace the wire back from the device past switche(s) to the fuse. After one or two devices you will know what each fuse does so you will no longer have a problem.

Check the fuse either by swapping it out with another or use your multimeter on resistance range to check that the fuse still has a low resistance i.e. it isn't blown. If the fuse is blown we have a different sort of problem see the section on blown fuses.

So we have a possible wiring or switch problem you will need your wiring diagram, your multimeter and your long multimeter lead. Connect the long lead to the negative terminal battery and to the negative terminal of the multimeter.

First measure the voltage across the battery, or if the engine is running from a known good point (generator output/ fuse box). We shall call this the "system voltage". It should be 13.8V or about 15V respectively.

Using the wiring diagram you need to work out which is the positive side of the device. Check that the colours match those on your diagram. If not check again and if you still think that you are right mark up the change on your wiring diagram.

[ Note :- On some devices such as window winder motors the "positive" side of the motor changes so that for winding up one terminal is positive, and for winding down another terminal is positive. On some other devices - e.g. temperature and fuel gauges - the positive supply goes through a device called a Voltage Regulator, this ensures that they are supplied with a constant voltage (about 10V) so that whatever the state of the battery and generator the gauges will always read the same. ]

Measure the voltage here when you try to operate the device. This should go from 0 to almost (-0.1V) system voltage as you press the switch. If it is much less than the system voltage repeat the measurement. If it is still less than the system voltage you have a problem between the device and the supply (battery/generator).

If this voltage was system voltage before operating the device and it dropped significantly you have a problem between that lead and the supply and the device is "negative switched". With a little checking on the circuit diagram you should be able to find a switch between the device and the ground. If this isn't on the diagram then there has been a PO modification and this needs to be added to your circuit diagram.

Now measure the voltage on the negative terminal of the device, same procedure measure with the device off, then switch it on. As you switch the device on the reading should settle to 0.1V to 0.2V range. If you have a higher reading - say 3 volts - you have a problem with the earth connection of that device. If you get a reading that is half the system voltage (about 7 volts) check your wiring diagram and make sure that this isn't a pair of '6V' devices wired together to make a 12V device (Very very rare). Note any differences from your wiring diagram.

So now you know if the problem is on the ground side of your appliance or on the supply side (or both!)

So what next? You repeat the procedure for the next component in the circuit in the direction of the fault. Till you are certain of the problem.

But the wire disappears into the loom and I don't know where it comes out so where do I look next? You have now found the reason for colour coding. You will have an idea where the other end is, so check there for a wire of the same colour coming out of the loom. If this fails you just have to follow the loom till you find the wire exit point.

It the problem is that the connector is corroded, it should be cleaned with wire wool, lubricated with copper grease and reconnected. If they are not tight the female element should be gently compressed with a pair of pliers till the connector is tight.

If the problem is a wire with some snapped strands (most common just by the crimp connector) then the wire needs to be replaced. Take a wire of the correct colour and strip one end. Crimp on to this the correct connector for the most difficult to reach end. Plug this in place of the damaged wire, fold the damaged wire back and tape it to the loom. (Some people prefer to cut the wire off, but that can leave sharp ends that may do some damage.) Tape the new wire to the loom remembering to leave a suitable amount of slack. As you approach the other end you will be able to estimate where to cut the new wire, strip it, crimp it and connect it up taping up any spare to the loom.

If the fault is a ground fault the next component is the grounding point it will probably not look dirty and corroded. You need to clean all the surfaces till they are bright, protect the connections from corrosion. I prefer to paint the chassis and when dry I bolt the earthing point up with a good smear of copper grease and a crinkle washer.

If you have a switch problem you could try a dose of switch cleaner, but in general they are sealed units.

But it still doesn't work!

You may find that after all you're hard work and adulation at finding a fault that the component still doesn't work. It is possible that the repaired fault wasn't a fault at all or that it was and was masking another fault.

All you can do is start the process again and proceed till you find all the faults or the real fault.

Fuse Y keeps blowing

A fuse that blows, you replace it with the spare which follows the fate of the first one to oblivion.

You have developed a short circuit - a very low resistance path has developed between the power supply positive and return. Most of the fuses on the original wiring served more than one group of appliances. If, for example, a fuse has been added for the headlight circuit then you have a relatively small search area for the fault, but the process is the same.

Take your multimeter and connect the long lead to the battery negative terminal. Select a low resistance range, and turn off all equipment supplied by that fuse. If necessary turn on the equipment that causes the fuse to blow and measure the resistance of the non power-supply side of the fuse to the negative terminal of the battery. If you have a value of <1ohm you have a short

Now you have confirmed the fault by measurement it is time to divide and conquer. Unplug each of the fused circuits one at a time repeating the measurement each time till you have found the circuit with the fault on it. Trace this wire, at each connector break the circuit and determine on which side the fault is, one side should have no circuit (very high resistance) to the battery, and one should have a low resistance to the battery. Once you have identified the wire segment or component that is the problem a visual inspection should reveal the problem.

What if the fuse blows every time the brake pedal is pushed? Then it is likely that the problem is in the circuit between the break switch load to the lights.

Removal and repair

If you have a loom with a badly modified section that is causing trouble, and you have a free weekend, you may like to replace it.

Start with a box of sticky labels and label up all the loom ends. Write any colour differences down on your working schematic - transfer these later to your master copy. When everything is labelled you can start unplugging things. Make notes about loom routing.

Now strip out and repair/renovate any items that need work.

Lay out the loom in a suitable sized area - kitchen garage etc. - note any permanent bends in the loom.

I like to tie down one end of the loom with a cable tie, this keeps all the wires in approximate alignment. Measure the distance from one end to where the wiring branches on the loom. Inspect all wires for damage, burn marks and the state of the crimps. Pay special attention to any that are used in circuits that you have been having a problem with. Run down each wire bending it through 90 degrees with a 20mm radius, any breaks will show up as a sharp kink in the wire. Take your multimeter and measure the resistance of all of the leads. You will soon get used to the values you should be seeing, but they should all be less than 0.5Ohm. Any wires that your are unhappy about should be replaced, remember to label up the new wires otherwise you won't know where they go.

Now you can start to tape up the loom. Remembering to tape out the branches at suitable points. This can be an art in itself. It is important not to use insulating tape as in the heat of the car the glue melts and migrates, making the loom very sticky. For the "manufactured" look you should use PVC wrapping tape, this is just like insulating tape but is not sticky. The technique is to tack the ends with some glue and then wind. Also remember to tack the tape at joints. Alternatively you can use spiralbind - but this collects dirt or lacing cord - if you have plenty of time.

Now the loom can be refitted.

Replacement or Upgrade

So your loom is past it. The copper has become brittle and is falling apart or it now has so many PO modifications that really it is past it.

If you are fitting a bought in loom then your only problem is finding the correct connectors for the right ends.

But if you want to fit new equipment, an immobiliser, an alarm or a stereo, or you can't afford a new loom then you need to make up your own. You will have to be very clear what the wiring diagram will look like and where you are going to mount the items relative to the loom so that you can get all the dimensions right. You will also need to work out the correct wire gauge for each circuit and it's colour. Write these down you will be using it soon

You will need a board (block board or plywood) the size of the final loom some screws and some cup hooks. You need to screw the cup hooks into the board in an arrangement that will give you the shape of your taped loom, as you add the wires they will sit up where the cup handle would be. You will need to add screws and other cup hooks as you go. Now put a screw in where the first connector would be and a screw or cup hook where this branch will join the main loom. Make sure that the branches are longer than you need and attach the first wire to the (use a cable tie or knot it) end screw. Route the cable around all the cup hooks of the trunk of the loom till you get to the end location and tie the wire off. Now add more wires till the loom is complete. Once all the wires are on the board you can start taping up the loom. It is a bit awkward around the hooks and screws, but it is work the effort. Now you will have a loom that should fit your car as you intended but without connector on. When you offer up the loom you should find that the branches are much longer than you need. Attach the loom to the car and then you can start cutting and terminating the branches as appropriate.

It will take you a while but it you take your time and be patient you will have a fully custom loom that fits your car perfectly.

A little note about battery connectors. These need really good cable and to be crimped really well. Most auto electricians will make you one up if you ask nicely for not much money. The crimping tool for these is about UKP125 so it is a bit expensive for the number of times that an amateur will use it.


I think that there are some upgrades that are worth putting in to improve the performance of the car.

Ground Bonding

Having accused the elan chassis as having not enough metal to make a good conductor I recommend that a lead is made up that runs from the battery to the engine (or may be the front lights). This should have side crimps on it that should be bolted to all the earthing points along the length of the car. For a lot of car's this improves starting and headlight efficiency.

Brighter headlights

To do this you will have to fit a new wiring loom for the engine bay that includes some relays for switching more powerful headlights.

More Expansive fuse box

In modern terms the Elan has pitifully few fuses so a new bigger fuse box is a good idea.

But where can I get all those wire colours?

I have three suggestions.

  • You could try buying the colours you need from an auto electrician. However most only stock black these days.
  • If you know several people rewiring/ modifying the wires in their car than it can be worth buying reels.
  • Go to a scrap yard and get old looms of wrecks and strip them for the wire colours you need.

I hope this helps