Testing gauges
Thread Starter
Racer
Joined: Jun 2001
Posts: 460
Likes: 0
Testing gauges
Hey guys, I've been rebuilding my 76 (never had it running !) and am about ready to fire it up . I've been trouble shooting the electrical system and got my center gauge cluster hooked up tonight. I do have a new wiring harness in the car.
Is there any way to test the gauges before starting the car up ??? After I hooked the power to the center cluster, both the fuel gauge and oil pressure gauges pegged out................... being as there is no gas in the tank and the engine wasn't running , I can only assume both these gauges are bad. There was no movement in the ammeter and water temperature gauges............... so I don't know if they will operate or not -- they are sitting on zero....... so I don't know !
Thanx for the help , Rick
Is there any way to test the gauges before starting the car up ??? After I hooked the power to the center cluster, both the fuel gauge and oil pressure gauges pegged out................... being as there is no gas in the tank and the engine wasn't running , I can only assume both these gauges are bad. There was no movement in the ammeter and water temperature gauges............... so I don't know if they will operate or not -- they are sitting on zero....... so I don't know !
Thanx for the help , Rick
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
yea you have something grounded, bad gauges don't peg, they stick or don't work at all. Disconnect the oil pressure sensor and power it up again, if it still pegs start tracing wires. Same for the gas gauge
Thread Starter
Racer
Joined: Jun 2001
Posts: 460
Likes: 0
I guess I should have said that they don't move at all when power is on....................... the fuel did move from half full to full, and the pressure moved from low to max initially................ but don't budge at all from the new readings --- with or without power ! That's why I'm thinking that they are bad, since they won't return to zero.
Thanks for the input guys, Rick
Thanks for the input guys, Rick
Le Mans Master
Joined: Aug 2006
Posts: 7,417
Likes: 1,554
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Bench testing gauges.
Fuel Gauge:
Apply 12 volts to bottom post and ground to top post-needle should now go to EMPTY.
Connect ground to center post-needle should go past full.
Battery Gauge:
Connect ground to top post and just touch 12 volts to bottom post-needle should deflect to minus.
Connect ground to bottom post and just touch 12 volts to top post-needle should now deflect to plus.
Temp Gauge:
Apply 12 volts to bottom post and ground to middle post-needle will go down.
Connecting ground to top post makes needle peg past high.
Not sure how to bench test Oil gauge but with gauge installed in center cluster and key on-remove wire from sender ( on motor ) gauge should now read high.
Ground same wire-gauge should read low. PG.
Apply 12 volts to bottom post and ground to top post-needle should now go to EMPTY.
Connect ground to center post-needle should go past full.
Battery Gauge:
Connect ground to top post and just touch 12 volts to bottom post-needle should deflect to minus.
Connect ground to bottom post and just touch 12 volts to top post-needle should now deflect to plus.
Temp Gauge:
Apply 12 volts to bottom post and ground to middle post-needle will go down.
Connecting ground to top post makes needle peg past high.
Not sure how to bench test Oil gauge but with gauge installed in center cluster and key on-remove wire from sender ( on motor ) gauge should now read high.
Ground same wire-gauge should read low. PG.
Thread Starter
Racer
Joined: Jun 2001
Posts: 460
Likes: 0
Pete........................ you are the man !!!!
I tested the gauges tonight and found that they are good. The oil pressure gauge didn't function back to zero until I disconnected the wire from the sender................... once I hooked it back up, it stayed on zero once I turned the ignition on again !
As for the fuel gauge, it must be a short somewhere like the other guys said........................... I used an old taillight harness, so I'm going to run some extra wires to check it out............... hopefully, I won't have to pull the tank out !
Thanx again guys.................... I'm getting closer ! Rick
I tested the gauges tonight and found that they are good. The oil pressure gauge didn't function back to zero until I disconnected the wire from the sender................... once I hooked it back up, it stayed on zero once I turned the ignition on again !
As for the fuel gauge, it must be a short somewhere like the other guys said........................... I used an old taillight harness, so I'm going to run some extra wires to check it out............... hopefully, I won't have to pull the tank out !
Thanx again guys.................... I'm getting closer ! Rick
Thread Starter
Racer
Joined: Jun 2001
Posts: 460
Likes: 0
Hey guys, thought I'd give you an update............
After running a direct line to the tank, the gauge still pegged, so I pulled the tank out again. I do have an aluminum tank with aftermarket gauge in it, and it was never hooked up before. I figured proper parts had been installed............... wrong !
I tested the sender with an ohm meter (with the tank normal and upside down and found out the ohms are 240-30..................... wrong sending unit !!! I need 0-90 ohms. Never assume anything................. it might come back and bite you in the butt !
Got a new one on the way from Summit.
Thanx for the help guys ! Rick
After running a direct line to the tank, the gauge still pegged, so I pulled the tank out again. I do have an aluminum tank with aftermarket gauge in it, and it was never hooked up before. I figured proper parts had been installed............... wrong !
I tested the sender with an ohm meter (with the tank normal and upside down and found out the ohms are 240-30..................... wrong sending unit !!! I need 0-90 ohms. Never assume anything................. it might come back and bite you in the butt !
Got a new one on the way from Summit.
Thanx for the help guys ! Rick
