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I noticed that after I drive around for a while (15-20 minutes), the battery gauge slowly creeps down out of the green onto the border line between green and yellow. Is this normal under operation? I hooked a charger up and both batteries were indicated at ~75%. I have the 100amp system.

does the 100amp system have a solidstate regulator or the old coil and relay type? it sounds like either your regulator or generator is only producing power when it's cold. at least mine, stays 100% even during long drives.

I have the original 25amp generator, but changed out the regulator to a solid state one and went to the colored charging gauge instead of the original amp guage. My truck is at the top of the yellow with the ignition on but truck not running. When running it is always mid green.

I think you have a definite charging issue. I'm betting it is the voltage regulator

I've been tied up with work travel, but finally back home and had a chance to take a picture of the regulator. It's made out of plastic, which makes me think it is newer. Any thoughts on what type it is?



Another thing I noticed is that with the ignition on but engine not running, I can hear/see a spark occasionally jumping around in the alternator.

i've never seen a plastic one, but i've never seen a 100amp system in person either. it's smaller than the big original ones so that's a good sign that it's a solid state system. it might be worth just checking the connections and making sure that there isn't a bit of corrosion going on, the solid state regulators don't usually go bad. at least not part way...it's usually all or nothing when they go

[quote]Another thing I noticed is that with the ignition on but engine not running, I can hear/see a spark occasionally jumping around in the alternator.


Sparks jumping across a Gen or Alternator is not a good thing. I wouldnt run the truck until you find out what going on...

Sal

I have the 100 amp system in my 51. It has the same regulator as yours, which is a solid state. The 1/8" plug above and between the two harness plugs is an access port for charging adjustment. Spec calls for it to be adjusted to approx. 27.5 volts. Carefully turn the adjustment with a small screw driver after removing the plug. Measure it at the batteries with a volt meter, as you make adjustments. Since the 100 amp system uses an alternator, the fields are rotating, and use slip rings for the brushes. There should be virtually no internal sparking from normal charging operation. Mine is somewhat noisy when charging low batteries, but it gets less as the batteries top off.