VCCA Home Forums TECHNICAL - GENERAL Electrical - 6 volt Rpm’s drop when the car door opens and the dome light comes on

Rpm’s go from 875 to 675 when the dome light or radio is on? 54 6volt system.

Generators don't charge at idle. Less voltage going to the ignition system because of the voltage going to the bulb would be my guess. Things like that are why I converted to an alternator.

I do not know the answer to this but is that not a large drop for a dome light? In my 41 I can turn on my headlights and I see the amp meter drop to the discharge area but do not notice any change in idle, no tach on the car so just going by engine sound. I would think that while at idle a good battery should make up the difference.

One wouldn't think so but it's the only electrical device that activates when the door is opened and there's no mechanical linkage between the doors and engine. If it only happens when the door is opened and stops when the door is closed there isn't much left to look at.

The only thing I can think of is there is a short in the line to the dome light that draws much more current than the bulb. If that is the case the wire will get very hot which could result in a major problem.

The wire to the xdome light is hot all the time.The switch is only a ground to complete the circutTry removing the bulb and see what happens

More info the engine drops 200 rpm when the dome light, headlights, radio, turn signals are used. Not the heater fan or brake lights.

The rpm’s don’t change with the bulb out.

There's your answer. Could be the connection is corroded enough that the resistance is causing increased current draw? If nothing else you now know the cause of the issue.

Converting to an alternator is avoiding the problem, when the vehicle was new this was not a problem, the generator system provided many years and miles of service. Is the dome light controlled by door jamb switches? The jamb switches, switch the ground portion of the dome light. Is it the original wiring harness? What is the voltage at the battery at idle? What is the voltage at the battery at 1200 or so RPM with no load on the electrical system? What is the voltage at the battery at 1200 RPM with dome light on? What is the voltage at the battery with the headlights on? Is the belt tight on the generator? How old is the battery? How good are the connections? Is the chassis ground good? The ignition system appears to be deprived of voltage which is causing the RPM drop in my opinion. Could be as simple as a set of brushes on the generator, or a voltage regulator, or a parasitic drain through the ground on the jamb switch which could involve some determination and some working electrical knowledge and GOOD volt ohm meter to track down.
There a lot of variable that could be causing this, and an alternator is not going to fix it just hide the problem.