Sudden Electrical problem

Started the car last night, and as I did, noticed that the ignition warning light did not come on.

It started fine, and ran well.

It was late, so I shelved the inspection until today. Here’s my findings:

What doesn’t work:
ignition warning light
indicators
windscreen washer
side window motors
rear demist
fuel guage

The PO rewired the car to (what I consider) a vg standard, but it may not follow the original diagram. It has given me virtually no problems in nearly 3 years.

The fusebox on the bulkhead is a 6 way box. The bottom 3 connections are always live, the top three are ignition-fed. All these fuses are intact.

To add, there is one odd happening:
After the ignition key is turned to the point where one should see the ignition light illuminate, the tacho jumps to the 500 rpm mark, and sticks there until the ignition key is turned off.

With this number of problems, I’m thinking a fuse or junction box type of problem. but I don’t know the Elan electrical layout anywhere near well enough to know where to start.

So any suggestions would be much appreciated please.

Regards,
Stuart.

I would start by checking as many earths (ground) connections as possible, the tacho problem is a classic sympton of a bad earth.

Hi Brian,

I managed to talk to the PO just after the original post. He confirmed the six way bulkhead fusebox is / are the only fuses.

He also said that if the main beam indicator light is still working, then it’s unlikely to be a multiple earth issue … just checked, and it is working.

His and my feelings are that “something” has dislodged from ether the speedo. tacho or ignition switch area.

Goes without saying that no work has been recently done in these areas, nor that I can see would affect the electrical system in general.

Thanks.

Stuart, while he may very well be right as he wired the car I find it odd that a live (power) connection (if disconnected) would cause the rev counter to give a reading… but on the other hand a bad earth would give such a fault as the circuits are trying to earth through a resistance (rev counter in this case) as there is no direct path to earth to compleat the circuits…but hey its a Lotus and there are no ground rules (pun intended :laughing: )

Difficult to fault-find on a bespoke wiring scheme but… you say that the fuses are intact, have you taken each one out and ensured that there is no “fungus” growing between the fuse and contacts? Given the tacho issue this seems an unlikely cause and I would go with Brian on the earthing route, but it is worth a quick look to eliminate.
While you are pulling the fuses out it would be worth making a note of what each one does protect, for future reference.

turn the ignition switch to where you would normally see the ign warning light and measure the voltage on both sides of the load (lamp). If you have 12v on both sides you have no ground if you have 12v on one side and say 4v on the other you have a bad (corroded, loose, etc) ground. If you have 0v on both sides you have a problem on the source side (eg bad fuze, bad ign switch, open wire, bad connection)

You can do this with any of the circuits that are not operating. (The circuit has to be on to do this voltage drop testing.)

Stuart,

Assuming you have a +0, remove the right side under dash trim. The dash is attached to the backbone chassis via two bolts either side of the shifter. The right bolt also serves as a ground connection. (On my car, both of them do.) Turn on the accessories that don’t work, reach around the back of the dash, and manipulate the ground wires that are attached to the right side bolt while keeping an eye on the accessories that are not working. If any of them come to life, you have found your bad ground. I’m not sure if the right hand bolt is the one that is giving you trouble, but this is where I would start. Best of luck.

Hi,

Thanks all for your help, but I’m not at all sure that it’s a ground/earth issue:

If I provide a new earth to the warning light or the fuel guage (with the ignition light on ) … nothing.

However, if I provide a new supply to the fuel guage … bingo, it works.

So ?
Where to look, please?

Regards,
Stuart.

So go back to the fuse box and attach a hot wire to the supply side. If that doesn’t work, try the other side.

Hi Frank,

There’s no problem with the fusebox/fuses. It seems to be a power issue further down the line.

BTW, I’m working from the S4 wiring diagram.
Does anyone know if there is a specific Sprint diagram ?

According to my 1970 edition manual wiring diagram, the voltage regulator should be mounted on the back of the tacho, but on my Sprint (71) it’s on the speedo.

The diagram shows the feed for the fuel guage is fed from that, and since I know the fuel guage feed is dead, I’d like to trace it back.

Being dumb … is there any particular knack in removing the speedo ?
Does it remove just like the tacho ?

Reason I ask is because it seems welded in place even after the two clamps are removed.

Thanks and regards,
Stuart.

I would try disconnecting the speedo cable - This will certainly stop you from pulling it forward

Dave

The speedo & other gauges should have a thin rubber ‘gasket’ (more like an ‘O’ ring) between the bezel and the front of the dashboard. This seems to glue itself to both parts making it seem like the gauge is welded in. Careful ‘jiggling’ should free it enough to peel the ‘gasket’ from the dashboard so that it can be removed undamaged & re-used. :slight_smile:

:arrow_right: Matthew

Stuart,

First of all, as the S4 and the Sprint are identical electrically, there is no reason for a seperate dedicated diagram for the Sprint although I think I recall seeing one somewhere.

Second, the device on the back of your speedometer is not the voltage regulator. It is the voltage stabilizer. It powers the fuel gauge. There is a green wire coming off the fuse box that powers the voltage stabilizer along with all of the other devices you mentioned with the exception of the ignition warning light and the window motors. That’s why I wanted you to check for power coming to and from the fuse box.

If you have found that the green wire coming out of the fuse box has power, then understand that it goes through a series of Lucas connectors so that it can split the power to the rest of the devices that it feeds. The fact that so many devices have failed indicates that the power is not getting through one of the early connectors in the green wire circuit either because a wire has pulled out, broken, or more likely, has corroded in a connector.

Starting at the fuse box, use a test light to test the green wire connectors until you find the bad one. As these devices work with the key, you must have the key on while conducting the tests. If the original harness is still covered in electrical tape, you will have to remove it in order to get access to the connectors. That’s not so much fun, and that’s why I suggested you save yourself some trouble and start at the fuse box.

Think of the green wire circuit as a tree and the fuse box as the base of the tree. You must go up the trunk to each branch and check for power until you find the bad connection (or branch). Good luck.

Hi,

I posted a reply between Dave and Mathew’s last posts, but where it’s gone, Lord knows !!

Apologies: voltage regulator was a typo.

Speedo loosened … correct, it was the rubber seal (thanks).

Will assume the “dying fly” position tomorrow night and try to chase this down.

Regards and thanks for the continued help,
Stuart.

Many call this the “Lotus position”. Removing the seat and steering wheel helps.