Major Electrical issues

[LoTex]

My 72 Elan Sprint has gone haywire, literally. It's been a progressive thing- first the lights wouldn't work, then the windows, then the wipers,. Finally the Rev counter started acting up as well. She continues to start but pretty much everything on the panel that is electrical is no longer working.

My mechanic is at a loss for what the problem is- here is his description:

As a background this is a car that has been converted to an alternator with wiring changes done at the old regulator. The conversion was done several years ago and all systems were working until recently. The battery is charged with tight connections at all attachment points. We suspected a problem with the ignition switch and have installed a new switch.

The power windows don't work. The wipers don't work. The fan doesn't work. The interior light comes on dimly when you turn on the wipers. The headlights don't work. Pretty much all the electrical doesn't work. We show 12 volts at the ignition switch at times, at other times it shows 8 volts. You can test everything and go back 30 minutes later and everything will have changed.

Any ideas?


Thanks,
Steve

[Concrete-crusher]

Bad earth, does all sorts of strange things. Start with the chassis at the back, then engine earth and rear lights to fuel tank and see how that works

Steve

[LoTex]

Good suggestion, thanks. We were having a grounding problem with the solenoid previously so maybe there is a more pervasive problem. Will keep you posted-


Steve

[steve lyle]

The interior devices use a ground at the right/lower dash mount bolt to the heater support bracket that’s bolted to the chassis.

Most of your issues sound like they’re related to the green circuit. But not the interior lights.

What’s the history of the car? Any chance someone tried a rewiring job on it?

I know you don’t want to hear it, but if it were my car I’d pull the dash and check every circuit /device. My guess is you’ve got multiple problems. Add a modern fuse box while you’re at it.

[Andy8421]

Bad earth, does all sorts of strange things. Start with the chassis at the back, then engine earth and rear lights to fuel tank and see how that works

Steve

Lucas car wiring (that the Elan is based on) was generally just about OK when there was a metal body to act as the earth return, but is marginal in the Elan when each component needs a separate earth. Whoever designed the wiring appears to have looked for the nearest bolt that went through the frame and used that as an earth.

As Steve rightly points out, the symptoms you describe are classic earthing problems, particularly one device coming on when you switch on another. I would recommend his advice, start with the point the battery cable joins the frame in the boot (a well known problem), then check all the other earths working forward.

The strange voltages at the ignition switch rather depend on where you were earthing you meter for the measurements. I wouldn't read too much into that until I was sure the earths were all sound.

[LoTex]

Steve, Andy-

I don't think it has been rewired. I'm the third owner and the repairs history I have doesn't show it.

We'll get on this thanks again for the excellent advice!

Steve

[HCA]

Steve is spot on. A good rule of thumb with plastic, and steel, cars is that when an electrical fault cannot be explained, it is earth.

Maybe it is time to re-wire the car. If you are not purist, then have someone do it from scratch with modern cabling. Bring the car to me and I will do it for free! I love re-wiring cars! On my +2, I have everything with a dedicated earth wire back to a single earth point on the chassis that is tinned - and still my wiring loom is half the size of the original...

[LoTex]

Thanks for the offer, Hal, but France is a bit too far for me these days!

We may wind up rewiring it when all is said and done.

Steve

[Bigbaldybloke]

I’ll second the poor earth comments, at one stage when driving down the M6 the fuel gauge started to show the tank filling up, if I had the wipers on and used the foot brake the handbrake warning light came on, windows wouldn’t operate, and various other weird things. All traced to poor earth behind the dash to the heater earth point and corroded fuses.

[LoTex]

I was experiencing something similar. First the windows wouldn't go up, then a few days later the Wipers wouldn't work, then the Rev counter started acting up. The petrol gauge was full one time, half the next, then full again...things were taking turns not working. I haven't gotten the final verdict from my mechanic yet but I'm quite sure it is the problem.

[The Veg]

My former Turbo Esprit used to do a weird thing in which the fuel and temp gauges would very slowly oscillate, adding and then removing about 25% of their readings over a period of about 20 minutes. A friend who had a TE from the same year had the same problem. He renewed the volathe stabiliser several times, his thinking being that it powered both instruments, but that didn't solve it. We both forgot about it after that. Then one day a couple of years later I was underneath, finishing with an oil-change and noticed that the engine-mount bolt that also secured the engine's earth-strap was loose. I tightened it without giving any second thought, but noticed during the next drive that the oscillation in the gauges was gone. I guess the temp sensor earthing through the engine is why the seemingly unrelated instruments (which you'd think would be earthed in the dashboard loom) were affected.

[LoTex]

Well guys, I'm afraid that it appears that the earthing of the car is fine. We are truly stumped now.

Any other thoughts on what may be causing these issues?


Thanks again,

Steve

[mbell]

Have you tested the battery? I'd be very tempted to test the car with know good battery before spending too much more effort on it.

After that I would be trying to map out what did and didn't work, then referring to the wiring diagram see if there any common point for the none working items. I'd probably also start measuring current flow from the battery to see if something triggers an unexpected high current.

Other thing could be some wiring damage bridging circuits that could cause "random" behavior. I'd have a close look for damaged wires, especially under/behind the dash.

You may be at the disconnect everything, test the wiring appear to be functioning correctly (e.g. live at right time) and bring things back one at a time to see if they work or don't work.

[Bigbaldybloke]

The other main common connection is the main power cable from the battery up to the starter solenoid, could this be damaged, corroded or have a poor crimp connection on it. Might be worth running a jump lead from the battery to the solenoid or even as suggested above, completely disconnect your battery and connect an external battery to the car with jump leads, again, I’d connect to the battery side of the starter solenoid and to the chassis at the front somewhere. My experience is on a Plus 2, but the principles are the same, on mine a good earth connection would be on the earth braid cable that connects across the engine mounting, that way you know you should have a connection to both the engine and the chassis.
When I first got my Plus 2 many years ago I know I ended up replacing this cable, it cost a fortune!

[vxah]

I was wondering where you got the ground from when you measured 8 volts at the ignition switch? If it was for example at the battery then it’s not going to be an earth issue?
From what I remember on the Elan all the power feeds start out from the starter solenoid terminal and split up from there. I’m thinking you have a corroding feed wire somewhere that drops the voltage as soon as you put a load on it?
Should be relatively easy to find with the aid of a circuit diagram and test light to a known good earth?