Pulsing panel lights

[Mark Hislop]

I have had this problem in my 73 P337. It is caused by voltage fluctuations in one or both alternators. This fluctuation is caused by resistance in the voltage regulator circuit. This resistance causes the alternator (or alternators) to "hunt", or increase and decrease there output by a volt or two.

First, try truning off one alternator at a time. The problem may be in just one circuit. Then, start measuring resistnaces or voltage drops in each segment of the voltage regulator circuit, including the master switch, the alternator field switches, the alternator field circuit breakers, and all of the little diodes and capacitors on the little circuit board mounted on the firewall. Clean all connections.

I had to replace the alternator field switches to get rid of my problem. They ohmed out OK, but there was enough resistance in them to cause the hunting problem.

Mark