I searched the above terms, not alot of luck but know i've seen these threads around.

Anyhow, the 96 GMC in my sig seems to be having these issues. Volts only seem to run steady on the scanner around 12.7v but the dash gauge fluctuates up and down, i'm used to seeing that gauge on other trucks right up around 13.5v, steady and IIRC the scanner showed similiar.

Oil pressure was reading 130Kpa (seems low to me) for the longest time, then all of a sudden it went up over 400Kpa, bounced around a bit then settled around 300Kpa. This is all at hiway speeds.

Everything on the scanner appeared normal during all of this. So i was wondering if anyone remembers what the causes were for this type of thing. I will be checking all grounds soon, also noticed the filter is on the IP plug, may remove it to check things out, but for now i'm busy with a 5th wheel install and additional fuel tank, i'm hoping this tank fits with room to spare in front of it for stacks! :D

I have soldered a ton of those clusters for erratic operation. You can sometimes get away with out soldering the push tabs to the printed circuit by just re seating them. Remove your cluster and flip it over,watch that trip knob. Take a small screw driver or even your fingers and push down on every one of those square tabs that make the connection between the printed circuit and the gage pins.

CR you should show more than 12.7 Volts as 12.8 is full charged(specific gravity) likely you should see 13.5. check at the back of the alternator, could be that the truck is not charging!

Hopefully i'll get time tomorrow to check some stuff out, been pretty busy pulling hitches and spare fuel tanks from the Cummins for this unit, fuel tank is in the welding shop for some refabbing. I should be putting all this stuff in tomorrow afternoon.

All my other units are being sold except the 00, i've run outta parking space!

One down and a couple more issues to go, batter terminals were real bad on the double connector passenger battery, cleaned it up and dash gauges pins 13.9 volts, i'll get them all cleaned up later and probably swap em for top mounts.

Ripped out the wooden box liner and rails, 5th wheel is in, spare fuel tank is in, still room in front of the tank for a custom set of stacks i'll have built, new 3" DP on the shelf waiting for time. Air bags will be here monday!

Performance mods to this point..... NONE:o:

CR whats wrong with the 94 and what do you want for it

Will send a PM.

Well i thought the problem was cured with the alt gauge on the dash and the OP's, apparently not. It did stay up around 14 for awhile then went back to its normal wavering from about 12.5 up to 13.5, all the time with a volt meter hooked to the batts directly shows 14 to 14.5 at the bats when running, ive gotten most of the grounds cleaned up, the dash gauge must run on a diff circuit, OP's still bouncing around also. Where does the alt dash gauge get its readings from?

Look right behind the passenger's side battery! There is a bolt there with 2 ground wires under it,one of those little ground wires will cause your dash functions to get funky!!

Nope, cleaned it already and its in good shape.

Just looking at the wiring diagram I have in the Haynes manual.

From alternator:

BRN ----> Charge indicator ----> Gauges Fuse 4 10A
WHT ----> Tach
BLU ----> Fusible Link 10GA ----> Right Battery
GRND = Case of alternator

That was the "starting/charging system" diagram. Looking at the "gauges" diagram now, the brown wire seems to go through everything in the cluster and the voltmeter get the signal from the whole instrument circuit.

Should have mentioned also:
BRN ----> Charge indicator ----> PNK Gauges Fuse 4 10A

Anyways, hope this info helps.
If you want the diagrams let me know and I'll scan and upload them.

Well i think its fixed now, while i was doing the exhaust & DP i cleaned the grounds on the frame there. Just drove for 4 hours and it never fell 1 needle width below 14. Keeping the fingers crossed now. Not sure but i think the OP's has steadied out about 1/2 way too.