soldave

Right, it's awards time! If you said that it was the alternator that was bad then you win... the prize that money can't buy: a virtual high five from me! Picked up the alternator today and the shop said that pretty much everything inside had burned out, and that it was impressive it was giving out anything at all! If you said it was a bad earth then you win...this! Yeah it's good enough and probably a bad earth or positive was put forward by the alternator shop as the cause of frying the internals. We've already seen the ground wire on the driver's side of the engine which is not exactly in pristine condition. If you said that I was just lousy at car mechanics you win... the honorary KBG Agent award for being harsh, but fair! I don't like car electrics and generally they don't like me. We just have that kind of relationship but it's something I do need to get better at. And that concludes the award ceremony so we'll go back to seriousness. I've got a new 345 amp rated earthing cable coming in early next week so that's going to replace that ground cable, and the alternator's ready to bolt back on. Once that's all done we can get the engine fired up again and see how our voltages are looking. I would love to give the car a full rewire at some point, but I doubt it would be cheap and I most certainly don't have the skills to do it!

I do. Actually When I said negative I should have said the thinner wire. Apologies - made a mistake there. Was still giving me some sort of continuity through to the battery terminal though, which does question my abilities! Tomorrow I'll do some more testing or resistance across individual wires, to see what I can find. Will probably start going negative battery terminal to where it grounds out, and then work from there.

Popped into the garage after work and cracked open the multimeter (does a multimeter open? Anyway, I digress). Did some resistance checking of wires. First, positive cable which runs from from alternator and eventually to battery. Result: close enough to zero for me to be satisfied. Then I looked at the negative wire from the alternator. 20 ohms of resistance running from alternator connector to the negative battery terminal. Checked a little further; around 10 ohms from alternator connector to coil, and 20 ohms between coil and negative battery terminal. Should I be getting this much resistance between these areas? Seems pretty damn high unless there's a special reason for it.

Good point. Those copper locking washers aren't so common to find, but I'll do some hunting tomorrow and find some. Will also clean up both contact areas when the new cable goes on.

That's a good call actually, on both strap and amperage. Will look into both straps and cables.

Got it. Thanks for doing the maths there. Does a 170a amp ground cable sound like it would do the trick? Would probably be happier with a cable over a strap, for reasons I can't explain!

Decided to take some guidance on the bad earth front and take off the earthing strap which runs from the driver's side of the engine down to the chassis. Bit of a pain to get off with a stiff bolt in the chassis partially blocked by a pipe going into the power steering rack (I believe). A bit of lost skin and swearing and I got there in the end. Now the earthing strap does look like it's seen better days! But I did some resistance checks across it and it was showing as having 0.8 ohms of resistance. That doesn't seem to me to be so bad. But it does look like it could do with renewing so that's what I'm going to do. Got my eyes on this (https://www.ebay.co.uk/itm/170-Amp-Car-Battery-Power-Earth-Cable-Choose-Colour-Length-Terminal-Hole-Sizes/222662654414), if 170 amps would be OK. Not quite sure on what amperage I'd need, so if that is way below what I'd want then please do let me know.

Old one that I thought was Lucas, sticker come off so no. Current one: https://www.ebay.co.uk/itm/LOTUS-ECLAT-ESPRITE-ELITE-UPGRADE-65AMP-BRAND-NEW-ALTERNATOR-1973-onwards/281723431091

Yeah it is looking that way. If it's confirmed, I'm wondering if I should get the latest eBay alternator rebuilt or the older Lucas one. Lucas one might have better quality internals (although needs rebuilding) but I'd need to modify the wiring a little. It has spade connectors only at the back whereas the current one connects through one spade connector and two ring connectors. Only a small mod but the less fiddling with wiring the better for me! Only chance would be if the Lucas alternator can have a threaded fitting to it so I can attach the ring connectors directly. None of that probably makes any sense!

Did another quick test of voltage output from the alternator instead of across the battery. 15.1 volts with accessories off and 12.8 with accessories on, using a chassis earthing point. My diagnosis continues, but will include some sort of testing of the multimeter itself too, just in case!

Right - a little more testing today. First off - took the battery to Halfords to check the condition of the battery; good news is that they said it's in perfect condition. Battery should have a CCA of 380, actual value 380. I also checked the electrolyte in the battery and (I think) it seemed all as it should be - pics are below. So we can scratch off a problem with the battery as the main issue. I also did another bit of testing voltages from cold (after the battery had been on the conditioner all yesterday afternoon and overnight). Started the car with and cold with no accessories the voltage across the battery started at around 13.7V, and then continued to increase to around 15.1V where it stayed constant. Put on fan, heater, lights, hazards and tested again and it had gone down to a stable voltage of 12.5V (revving did increase it). Voltmeter readings inside the car were 13.5 and 11V respectively, so it looks like that gauge is reading around 1.5V less than it should be, although that's not really the main issue here. I can understand the requests to check for a bad earth (especially when it comes to the rear lights, and I probably agree with that diagnosis, as the front lights are hardly dimming), but would a bad earth be causing that high a voltage across the battery with no accessories on?

Those voltages were when the engine was running. With all accessories on, revving the engine did raise the voltage to a peak of around 14.95v. Alternator belt doesn't seem to have excessive play in it. Lights at the front shown. Doesn't seem to be dimming there (or it's very faint) which would probably suggest an earthing issue on the rear lights.

Out for a drive today with the heating and wipers on, and noticed the voltmeter in the car dropping under 13v. Not done that for a while so it got my attention; I turned them both off to test and it crept back up. Got back home and pulled out the multimeter to do some very basic testing across the battery (I know not the most effective, but humour me). Did some measurements of the voltage; first with everything off, and then with the fan, heater set on full, lights and hazard lights on. With all the accessories turned off, voltage was 15.3v at the battery and showing a couple of needlewidths above 13V on the guage in the car. With accessories on, the multimeter was showing 13.2v but the guage in the car was in the red, just above 11v. I also looked at the rear lights. With accessories on there was quite a noticeable dimming of the rear lights when the hazard lights came on; with accessories off there was still a little dimming but not as pronounced. Does it sound like the alternator's on its way out? I did replace the Lucas one with an eBay special about 2 1/2 years ago, but it's done fine until now.

Good writeup and pics showing the state of play with the engine. Do you have a timeline for it getting rebuilt or is it just a case of when it all gets done?

Here's some Brexit driving information which I'm sure will change in the next couple of months. https://www.gov.uk/government/publications/prepare-to-drive-in-the-eu-after-brexit