Lucas prince of darkness

Hello all,
I’ve have an ‘86 90 that I recently put an electronic distributor in. 2 months later, the weights came apart inside the distributor body and ate it from the inside out. I replaced it with a stock unit and have the timing pretty much dialed in. I noticed on a test run this evening the when I turn on the headlights the gas gauge goes to full and the temp gauge goes to cold. Turn lights off they go back to normal. Just curious if anyone’s experienced this before I go down a diagnostic rabbit hole. I may just be coincidence and unrelated but figured I’d ask first. Thanks.

Lord Lucas is meddling somewhere

Why yes he is. I’ve looked at the (very vague) wiring diagram and may have found a common thread. Will suss it out in the daylight tomorrow.

4XPhyllis said:

Hello all,
I’ve have an ‘86 90 that I recently put an electronic distributor in. 2 months later, the weights came apart inside the distributor body and ate it from the inside out. I replaced it with a stock unit and have the timing pretty much dialed in. I noticed on a test run this evening the when I turn on the headlights the gas gauge goes to full and the temp gauge goes to cold. Turn lights off they go back to normal. Just curious if anyone’s experienced this before I go down a diagnostic rabbit hole. I may just be coincidence and unrelated but figured I’d ask first. Thanks.

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It will almost certainly be an earth issue - probably something to do with the tell-tale earths but could be the main earths at the sidelights are bad and the whole lot is trying to earth through a circuit it should not!

For example, with shared earths, if the earth becomes high impedance due to, for example, rust then the route may actually be easier for current to flow through the headlights and back up, for example, the indicator earth wire via the lamp filament, back up to the stock and via a strange route.

I had an earth off once for something and noticed that the headlights brought on about the whole dash but only if the indicators were on - basically out of interest I worked out the route and it was power back-feeding and grounding via other circuits. As soon as I remade the earth connection all was well.

+1 on the above. very likely an earth problem

Thanks guys. I’ll check all the “earths”, or “grounds” as we call them over here, not sure why in the US they have to word everything differently. Funny thing is, this evening she behaved fine. Timings dialed in so she’s running great again, dusk came and I turned on the lights and the problem didn’t reoccur. I guess with not much else to do on the weekends (because there’s nowhere to go but home) I’ll have a project! Cheers and thanks.