Electrical Problem
 

I jump started my 1969 GMC Pick-up but accidentally reversed the polarity when jumping. Now all the lights flicker when the truck is running. I relpaced the alternator c/w it's internal voltage regulator, battery and flasher relays and the problem still persists. Any ideas on what to try next?

Thanks,

Orange 920

Re: Electrical Problem
 

is the light switch on when this happens?

Re: Electrical Problem
 

Yes the light switch is on.

Re: Electrical Problem
 

i'd start by removing both battery cables and clean up all 4ends and where they mount to bright and shiny then reinstall the cables and see if that helps

Re: Electrical Problem
 

Make sure the alternator belt is tight and put a volt meter on the battery positive on the back of the alternator and to a good ground, if the voltage jumps around like your lights, go get another alternator.

Re: Electrical Problem
 

I think there is a possibility that you have blown one of the diodes in the alternator bridge rectifier. The large red wire on the back of the alternator comes directly from the battery and connects to this bridge ( see diagram).

When the polarity was reversed it may have caused the diode to blow which would have dropped the dc output to the large red wire circuit. It's also possible that one of the diode trio diodes has gone which would reduce alternator output.

I would check the alternator output with a voltmeter between the large red wire on the back and the best ground handy. If the meter flickers it indicates that output is rising and falling. do this at steady rpms of course.

You might also unplug the small plug on the top of the alternator and check the lights for flickering. This makes the alternator output go to zero and if the flickering stops that eliminates a poor connection on the light wiring circuits. Do this with the engine off to avoid residual magnetism in the alternator field from outputting voltage to the system.

My first thought was the same as yours, that it was the regulator. What is c/w that you say you changed?

Attachment 667403

notice that the large red wire goes directly to the bridge rectifier