Voltmeter - intermittenty maxing out

[suffolkfox]

Hi all. Car is our 350i project, 1985 series 2 body but stil swing arm suspension generation.

Symptoms - driving along then headlights and all other lighting gets brighter and the voltmeter needle hits the buffer off the maximum scale. After couple of minutes (sometimes few seconds) drops back and lights go back to normal (whips out candle to see where we're going!!). No problem starting, battery appears fully charged and charging. Any ideas as to what to check, what might be fault welcome.
Thanks
SF

[rev-erend]

I'm no expert but a guess - the voltage regulator on the Alternator is dieing.. wedgie or Dicky will probably know more.

[leorest]

The fact that instrument and main lights get brighter backs up the volt meter reading. So as Rev says the voltage regulator on the alternator is not doing it's job. Best to get it sorted ASAP as it will nadger your battery. I would think any auto electrician worth his salt would sort it in a jiffy.

[adam quantrill]

Check the thinner wire from battery + to the alternator - this is the sense wire, and if it's corroded or intermittent the alternator will give too much volts to the system, with similar results.

[rev-erend]

Check the voltage across the battery terminals and from a good earth to the back of the alternator..

You should get no more than 14.4 volts..

[suffolkfox]

Thanks folks, i'll get the multimeter out over the weekend and poke things. As it's possibly guilty, anyone know if the voltage regulator on the alternator is removeable or if it's a new alternator?
SF

[rev-erend]

suffolkfox said:

Thanks folks, i'll get the multimeter out over the weekend and poke things. As it's possibly guilty, anyone know if the voltage regulator on the alternator is removeable or if it's a new alternator?
SF

I'm pretty sure it's built in.. but I could be wrong..

[suffolkfox]

Better go and rummage around in the garage - when suffolkfoxy blew the engine up on the drive the new (but old) engine came with all ancillaries so somewhere I have an alternator that has done approx 10 miles during its 16 year life.

[suffolkfox]

Final word on this one for anyone searching in the future.
Tried the loose control wire but no change so voltage regulator was next thing. This IS built into the alternator, BUT can be replaced so don't jump to replace the whole thing. If you remove the black plastic cover and undo about 5 screws, its a Lucas 15TR, in my case the version with 4 wires, and takes about 3/4 hour to fit including removing and replacing the alternator. Apparently the brush cartridge can also be replaced fairly easily.

[rev-erend]

Did it fix the problem though..

[suffolkfox]

Sorry - yes fixed. Prior to replacement, plugged in multimeter and with engine running, stationary on drive so no jolts (trying to rule out further loose connections) and all electrics on (fan, headlights, etc) would run steady at 14.4Vish then suddenly jump to 17V+ for no reason then just as suddenly fall again. After swap solid at 14.3V irrespective of load both stationery and moving.

Thanks all for the support and help
Jerry