Electrical Oddity - Disco Lights on my P6

James Harris

New Member
I have a 74 3500s that seems to be nostalgic for the 70s.

Whilst driving the dashboard lights and headlights alternate on an entirely random basis between normal and really bright.

This seems to be accompanied by the ammeter jumping from normal (with the battery fully charged) to +lots (when lights go bright).

Not knowing a great deal about electrics I wondered if anyone could advise me? Should I be buying a new alternator, new control box, or new flares?

Thanks in advance!
 
I had a similar problem several years ago with my first P6, a 2200TC. It was a 1977 car, with the later type of alternator where the diode rectifier pack is integral to the alternator. From your description, it seems to be the same fault - the voltage output 'jumps' from around 12 - 14V to something a lot higher - your lights go really bright, and the ammeter goes way up !! This was caused by the diode rectifier in my case.

I would replace the control box first (4TR type ?) and see if that cures it. A word of caution though - if the 'overcharge' is happening for prolonged periods - as it was with me - your battery literally 'boils'. Mine discharged a lot of electrolyte all over the boot, and made a heck of a mess. Hope this helps.

Dave.
 
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