1940 Ford Convertible Lights Dimming

This is a very general response: I am unfamiliar with your vehicle.

The way the regulator works is to connect or disconnect 6/12 Vdc from the battery to the generator stator windings. The regulator makes these connections/disconnections based on the output potential of the generator. The way to tell if the problem is with generator or regulator is to to bypass the regulator function and apply 6/12 Vdc from the battery directly to the generator windings for a short period of time and observe the generator output, or headlight beam intensity. A short period of time is all you want here, because the full-on output of the generator may well be higher than the steady-state output, and you don't want to fry stuff.

Anyway, if you do this bypass and you still have a low voltage output, then the generator is bad, or the belt is loose or bad; anyway, it is generator-related. If the generator output is high, then it is good and the regulator needs your attention.

emc_c

Agreed, but OP would likely need more detail about how to bypass the regulator if he doesn't know.

A good chance it's the generator brushes, and these are easy and cheap to replace.

Cheers..........Codey

Measure the battery voltage and the voltage of the dim devices with a volt meter. What is the system voltage supposed to be, 6v or 12v? What is the voltage rating of the dim devices? A 12v lamp will be dim on a 6v system.

as mentioned by someone else.

you need to get a volt meter and

1 check battery voltage

2 check voltage at dim item there will be a few volts difference but no more than about 2/3 volts

3 you might need to check amps at dim item

4 supply more information

You are also looking at a 70 year old wiring system. It is possible that you have a wiring issue.

You need to follow the advice that peter stated above also clean the contacts at the battery, head lamps and all grounds. On older cars it is very common for grounds to be a problem.