'97 GMC P/U FRC Aux A + B dead.

[OleO]

'97 GMC 2500 pickup. 2WD. 8600 GVW. 5.7l (350ci) Vortec.

I have no power at the Aux A and Aux B terminals on the
FRC (Fuse Relay Center) under the hood. I tested with a
DVM, to ground, with the ignition key at each position. Off,
on or accessory. It appears there has never been anything
attached to either threaded terminal. Both, adjacent, 30 amp
fuses are good.

Is there a relay that needs to be pulled in to energize these
terminals? Are there fuses or fusible links between the battery
and the FRC?

I'm still trying to find a wiring diagram to trace the circuits back
to the battery.

[Bigdav160]

Are these the terminals? Looks like they are part of the same bus

[OleO]

This looks like the correct wiring diagram (or close enough). I'll have to do a
little detective work and a "stare and compare" to confirm it. I'll count the
number of ckts and vfy amperages to see if it's close.

The feed to the 2 studs is common to other circuits, which are functioning...so
I'm a bit perplexed right now. The 30 amp fuses have an element large
enough to visually inspect and insure continuity, although I tested across
them with an ohmeter as well. They were still plugged into the fuse block, but
this shouldn't be a problem. I stuck them in the test points with the DVM
leads.

I traced the heavy lead from the battery to the FRC to see if there was a
fusible link but didn't see one. This was before I saw working ckts also feed
from the same battery lead as indicated by your schematic. The cable is a
bit difficult to trace under the FRC, but I believe I traced it thoroughly.
This is where I think I'll re-visit. I saw no power where the battery lead
terminates. I thought it odd, but it was the end of the day and I had to
wrap things up. The leads on my DVM test OK. They're plugged into the
correct jacks on the DVM. I had the meter set to DC volts with max scale
set at 20 volts. The setup was correct to test for DC volts. The only thing
I neglected to do was check for voltage at a known, working source, the
battery. This will be my next step. Tomorrow. Could it be as simple as a
defective voltmeter? Could I actually have power at Aux A and Aux B studs?
When you don't see what you should see, and there is a high probability
that you should see it.... test your test equipment. I'll keep you posted.