Gauges dont work help
 

So I was hoping you guys could help me on this. i have a 2nd gen 12v 5.9 and only my gas and oil pressure gauges work. Ive heard that it could be a crank position sensor or the dashboard itself. this all started when i hooked up my lightbar and it flickered a little bit then decided to take a **** on me. ive checked the fuses and relays but those are all fine. ive been trying to figure this out ever since i got the truck 3 months ago.

First, there is no CPS on a 12-valve - there is an Engine Speed Sensor. CPSs are on vehicles that have injection/ignition functions that need to know what cylinder is at top-dead-center so they know what injector (and coil, for spark-ignition engines) to energize. The following is from my AllDataDIY subscription for my '96 (yours may differ if you have a different year) - their info is obtained from the factory. This concerns the power/ground feeds for the cluster:
"The instrument cluster contains the gauges and warning lamps. All gauges have magnetic movements.
When the ignition switch is in the START or RUN position, circuit A21 feeds circuit F14 through a bus bar in the fuse block and fuse 12. Circuit A1 from fuse 3 in the Power Distribution Center (PDC) supplies voltage to circuit A21.
Circuit F14 provides battery voltage for the warning lamps (except seat belt indicator lamp), transmission up shift lamp, and all gauges.
Circuit E2 from fuse 13 in the fuse block feeds the illumination lamps. Circuit E1 from the headlamp switch powers fuse 13 when the parking lamps or headlamps are ON.
Circuit Z3 provides ground for the indicator lamps and illumination lamps. Circuit Z11 provides the ground path for the gauges"

I could be wrong (someone chime in if so), but I don't see anything above that suggests an ESS signal is needed for the voltage and coolant temperature gauges. Did you check the fuses both in-cab and in the PDC?

The headlight switch wiring is notoriously weak in these trucks. How did you wire the light bar, and what's the current draw on that bar? If you tried to run a light bar off the stock wiring without using a relay to power it off the battery, you could have overdrawn something.

What year is your truck? I don't see any details in your signature line. If you tell us the year, I may be able to send you a link for downloading the factory service manual - once you have the FSM, you can trace wires and do more diagnostics.

its a 1994, ive checked all the fuses in the cab and fuse block, I have the light bar off now but I did hook them up to my headlights and i feel very stupid for doing it but i dont know where to start to look for the cause besides fuses.

Downloadable FSM for '94... (linked from a sticky on another Ram Cummins site) - CD & paper copies here

You say your oil pressure and fuel-level gauges work, but your coolant temp and voltage gauges don't work at all? No reading at all? I would check the operation descriptions and wiring diagrams in the FSM for every circuit going through the headlight switch (remember, its notoriously weak) and the gauges/cluster - if there's anything in common, that would be top of my list... Pull the headlight switch and see how it and the connector look. When I bought my truck (well used), the switch and/or connector had obviously overheated. The connector block looked like it had been heat softened and I think at least one of the partitions between connectors were gone, and one or more terminals on the switch itself were loose.

Do you have a multimeter?

Just for grins and giggles- did you check both fuse boxes- under the hood and on the driver's side in the dash?
Did you check all the fuses for continuity out of the vehicle?

Just looking at these little buggers can lead you on a wild goose chase.. (DAMHIK)