27 shows discharge on ammeter when lights are on

[Guest morerevsm3]

Hi all, ammeter shows charge when running (up to 20A) , although it tapers off the higher you rev it, but with lights on, it discharges all the time, anyone elses do this, or do I have a problem that needs fixing?

[Matt Harwood]

How much discharge are you showing? These cars (and their generators) were typically built for slower speeds, and full charge will be achieved between 25 and 35 MPH. Below and above that, it won't charge as well. I've noticed on my '29 Cadillac, which probably uses the same generator, that with an electric fuel pump and driving at night, the headlights and generator will pretty much fight to a standstill. I know the generator is adjustable, but to have it charge sufficiently to run the headlights, you will be over-charging during the day when not using the headlights, which is murder on batteries. I have a solid state voltage regulator, which should cure this particular malady, but I haven't installed it yet. Unfortunately, these generators only put out as much as they can put out, and it isn't much. This is the primary reason I want to get the vacuum tank working on my car (eliminate one electrical draw) and switch to LED taillights (reducing consumption there).

Does this help? I think what you're seeing is normal, unless you're showing a major discharge with lights on at, say, 30 MPH. It should be pretty close to 0 at that point.

Let us know what you find. Good luck!