lights randomly going brighter and dimmer

[Craigb]

Been having a good run from my 96 110 tdi wagon. The last week has been on our scrub block, spotlighting, running arb fridge and without dual battery and didn't miss a beat. Leaving in the dark, towing a trailer and with spotties on, suddenly within a few km the lights went very bright, I would say abnormally bright because the highbeam warning light on the dash as much as anything looked distractingly bright. After a few minutes went back to normal. Didn't seem to matter if high beam, spotties on or off etc. After about 100km took the trailer off and still did it. At no time has the car not started and cranked over well. And if it was a load thing thought it would go dimmer not brighter.

Has this happened to anyone or any suggestions where I should look? Was expecting something to burn out but all seems good.

[Jode]

I'd suspect the alternator being faulty. Crank it up and measure the output at the battery terminals on idle - should be about 14.2V, but if it's over 14.4 then the regulator is likely toast. If you turn on the headlights the voltage should drop to about 13V and go upt to around 14V at 2000 rpm.

[BilboBoggles]

Sounds like the regulator in the alternator. Might be time for a reco. You can replace the regulator and the brushes yourself - but you'd probably also want to do the bearings at the same time. Easier to just get it reco'd.

A sustained high voltage could boil your battery. Might be worth measuring actual voltages to see what it's getting up to.

[Craigb]

Thanks for the replies. Will keep an eye on my battery for now. Also I have a 200tdi car here that I'm not sure the future of so might borrow that one for now - off in the opposite direction to the flinders this weekend - half my luck!

[wrinklearthur]

Just watch the pulley sit's in the same position forward in respect to the alternators mounting lug.
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