83 GMC Instruments Do Not Work

[67RS/SSx2]

Okay, the Beast finally arrived. It is a 1983 GMC Sierra Classic 2500 crew cab. It has a 350 SB and a TH400 tranny. It runs rough at idle and low rpm but smoothes out when the rpm is increased. I'll work on that later.

First thing I noticed is that none of the dash instruments work. The volt meter - nothing. The engine temp gauge - nothing (although I expected this as the previous owner installed a below-dash aftermarket temp gauge that does work). Oil pressure gauge - nothing. Gas gauge reads about 1/8th tank on both tanks (it has the aux tank) even after I added 6 gallons to the RH tank and then 5 gallons to the LH tank. When I switch between tanks nothing changes...I am not sure it is truly switching.

I do not yet have a service manual for this truck. Is there a fuse that could affect all instruments except the speedo? Any suggestions on where I should begin my search?

I'm just getting started but it looks a little overwhelming. A lot to do!

Thanks!