88 s10 2wd 2.5 litre will not run with the f terminal of the alternator connected. had alternator tested showed good but needle jumped around some,so went ahead and bought a reman. put it on same issue. no codes. unplug the f terminal vehicle will run.this is circuit 39goes to ign/gauge fuse 20A, which ties into the instrument cluster so i unplug the cluster no change.same fuse and circuit 39 go to ses lamp which should have been eliminated as a possible cause by unplugging the ipc.other places circuit 39 goes is ac cutout relay,shift lamp,vss buffer.anyway wondering if anybody else has seen this before i tear anything else apart on this rig.cleaned all my grounds.
This is a very specific issue and I am not an S10 expert but does this have an external voltage regulator? Or is it built in to the alternator?
internal voltage regulator
Did the problem occur after some other problem was dealt with? It occurs to me that if the engines was run with the BAT terminal disconnected from the alternator one or more diodes might have been blown. When the BAT terminal is reconnected AC current would interfere with the ECM.