"Jumpy" ammeter ???

[trudellt]

I've found a heck of a strange issue with my (FORD) charging system in my 514.

The first time I took my car out this year I noticed the ammeter always showed my system discharging. I found out two things:

1) Battery was load tested and I had a bad cell. I bought a new one.

2) Regulator was dead. The field always showed 0V. I bought a new one.

At least the system was "attempting" to charge now - but I have the following issue:

At about 1600 r.p.m., my ammeter needle bounces (a few times per second) between -3A and +25A.

At idle it sits at about -3A. At 1200 it finally crosses 0. At anything over 2500 r.p.m. it sits at about +3A.

I also have a fairly new alternator (1G type - 80A). I have also tried 3 gauges. They all read about the same. One is a lab-grade gauge I borrowed from work.

The regulator field signal is bouncing between 5V and 8V at 1600 r.p.m. which seems suspect - but it is brand new. At idle it shows about 10V (stable) and at 3 grand it shows about 4V (stable). That seems right - except for the "bouncing" near 1600. I just can't see how a regulator would fail in that mode.

Outside of the jumpy charging/discharging near 1600, it looks like I have a problem charging at idle as well. This problem is with no lights on and no fans on.

My grounds look good. I even went so far as to make a new harness at work. No luck.

I'm curious about the following if somebody has a minute to respond:

1) Has ANYBODY ever seen this?

2) Could somebody please tell me what their pulley set ratios or diameters are? I have an aluminum set but they are not March's. I'm trying to get an idea of the minimum alternator rpm's usually required to charge.

If anybody is interested: My regulator is marked IASF (maybe not that order). I is connected to ignition. A is connected to battery. S is connected to the stator on the alternator (but since I don't have a charging light it doesn't matter.) I've also tried disconnecting it. F is connected to the field on the alternator. The ground leg on the alternator is tied to the case of the regulator. The case shows no resistance to the chassis ground.

Thanks for any ideas.