Intermittent power drop when headlights are turned on

Posted by Mark Buckley On 2012/2/3 15:08:36

I'm having difficulties troubleshooting an electrical problem in my 1950 Standard Eight.

Some background: I've recently replaced the generator (rebuilt) and voltage regulator (brand new aftermarket supplier). A few years ago I had the car completely rewired with a setup from Rhode Island Wiring. My 6-volt battery is just a few months old and holds a good charge. To the best of my knowledge all wires and cables are the proper gauge and have corrosion-free terminals. Last autumn I replaced the distributor and had an electronic ignition installed. The radio and blower motor seem to work reasonably well. I replaced the headlight switch a couple of years ago, along with the hi/lo beam pedal switch.

Most of the time the electrical system runs well. There seems to be enough electrical power to run things just fine. HOWEVER... on some occasions when I start the car at night, and turn the headlights on, the needle on the charge/discharge meter on the dash swings way over to the left--discharge--side. It goes so far over to the left that it almost seems to peg out. The needle stays far to the left regardless of engine speed. If I rev the engine or let her idle the needle barely moves.

Sometimes I can 'correct' this by turning the headlights on & off a few times. Other times the only solution is to hope like hell I make it home before the battery goes. Sometimes it never happens at all. So far the pattern seems to be that if it doesn't happen right when I turn on the headlights then it's not going to happen during this drive. In other words, it hasn't happened during the middle of a drive.

Interestingly, when the needle makes its swing the lights don't seem to become noticeably dim nor can I detect a reduction in engine power. Of course, when it happens I immediately turn off accessories like the radio and blower, so I can't say for certain how the apparent power loss affects those units.

I'm wondering if the problem lies in the generator, the headlight switch, the ammeter or someplace else. I'm terrible fixing electrical stuff but I have a pretty good mechanic. Sadly, he admits he's not that good with electrical stuff, either.

Any ideas or suggestions on pinpointing the solution to my problem would be greatly appreciated!

All the best,

Mark