QUOTE(Spoke @ Jun 20 2024, 04:05 PM) 
QUOTE(mb911 @ Jun 18 2024, 05:39 PM)
dF is weird as I get different values depending on what 12 pin connection I check.
What does the 12 pin connection have to do with DF? In the 914/4, DF goes between the alternator and the VR and goes through the 3 pin connector between them. That's it.
Did you do some tests on the 3 VR voltages while running? This can tell a lot about your system.
When running, measure these voltages at the VR:
D+ should be 13-14V
DF should vary between 5-10V depending on electrical load.
D- should be 0V
Also measure the battery voltage:
B+ should be 13-14V and follow D+
Measure all voltages with respect to a chassis lug, not the engine case.
For the field test, remove the VR and short DF to D+ then start the engine. This should force maximum voltage of about 16V on D+ and B+. Do this for a short burst as it's hard on the battery and alternator.
As an aside, my '86 930 was showing low battery voltage (12V) and slow starting. I bought a new battery and immediately got 13.5V steady. You mentioned you were going to replace your 10 year old battery. Did you replace it and did it make a difference?
Changed battery, no change, did full load test and shot up to 15.5-16 volts short burst. Everything points to VR so ordered a new one. Waiting for that to be delivered
