72 C3 gauge issues
Thread Starter
2nd Gear
Joined: Nov 2023
Posts: 2
Likes: 0
From: Hamilton, Scotland
72 C3 gauge issues
I have a (new to me) 72 C3 and believe I have some electrical issues with the gauges and hoping there is a common electrical cause.
I initially noticed that I was reading no oil pressure - engine fires and ticks over fine, and sounds good. Then noticed no battery voltage reading and no change in the water temperature, so I'm thinking/hoping I'm simply missing a common ground or live feed to these? They were working a couple of weeks ago.
In addition I have the door ajar light on permanently. Fuel gauge also seems to work correctly.
So are there any common ground or live that may have come loose here that I can investigate? I did see a hanging wire with a ring on the end which looked like a possible ground hanging down by the starter - could this be it?
I initially noticed that I was reading no oil pressure - engine fires and ticks over fine, and sounds good. Then noticed no battery voltage reading and no change in the water temperature, so I'm thinking/hoping I'm simply missing a common ground or live feed to these? They were working a couple of weeks ago.
In addition I have the door ajar light on permanently. Fuel gauge also seems to work correctly.
So are there any common ground or live that may have come loose here that I can investigate? I did see a hanging wire with a ring on the end which looked like a possible ground hanging down by the starter - could this be it?
Drifting
Joined: Nov 2002
Posts: 1,787
Likes: 261
From: Blue Bell PA
2018 C3 of Year Finalist
Welcome ,please tend to the oil pressure first. There is a small tube coming from the rear of the engine
in to the dash. It is not an electrical ,unless something else was changed. The other problems can probably
be traced to a ground problem. Good luck to you.
in to the dash. It is not an electrical ,unless something else was changed. The other problems can probably
be traced to a ground problem. Good luck to you.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,137
Likes: 4,246
From: US-PNW
Have you removed the passenger dash panel? Easy to do with ~1/2 dozen screws, then you can see connections on the back of the gauges.
On the back of the oil gauge, is there a spaghetti sized plastic tube connected? That's the oil pressure line – it has a small bit of oil in it from the engine that presses on the mechanism at the rear of the gauge. (Do not disconnect the line from the back of the gauge and run the engine. You'll be cleaning up oil from behind the dash for quite a while.)
Does the temp gauge have the 3-prong wiring harness connector firmly seated? If so, go to the driver's side of the engine and see if the single wire is attached to the small temp sensor screwed into the head between the 1st and 2nd spark plugs.
The door ajar light is controlled by the plunger switch at the very bottom of the door latch end of the door opening. Is it there and does it plunge OK? You can unscrew it and gently pull the switch out to be sure the wires are on the contacts and not touching each other. Takes maybe 2 minutes to pull and put back.
On the back of the oil gauge, is there a spaghetti sized plastic tube connected? That's the oil pressure line – it has a small bit of oil in it from the engine that presses on the mechanism at the rear of the gauge. (Do not disconnect the line from the back of the gauge and run the engine. You'll be cleaning up oil from behind the dash for quite a while.)
Does the temp gauge have the 3-prong wiring harness connector firmly seated? If so, go to the driver's side of the engine and see if the single wire is attached to the small temp sensor screwed into the head between the 1st and 2nd spark plugs.
The door ajar light is controlled by the plunger switch at the very bottom of the door latch end of the door opening. Is it there and does it plunge OK? You can unscrew it and gently pull the switch out to be sure the wires are on the contacts and not touching each other. Takes maybe 2 minutes to pull and put back.
Racer
Joined: Mar 2014
Posts: 267
Likes: 24
From: Montevideo, Uruguay
In the case of the temperature gauge on the dashboard, to verify that it works, the connector that goes to the sensor on the left side of the engine can be connected to ground. If the dash gauge is working, it should quickly read the maximum temperature. If this happens, what would be bad is the sensor. If the needle does not move, you should check the wiring and the gauge itself.
Thread Starter
2nd Gear
Joined: Nov 2023
Posts: 2
Likes: 0
From: Hamilton, Scotland
Have you removed the passenger dash panel? Easy to do with ~1/2 dozen screws, then you can see connections on the back of the gauges.
On the back of the oil gauge, is there a spaghetti sized plastic tube connected? That's the oil pressure line – it has a small bit of oil in it from the engine that presses on the mechanism at the rear of the gauge. (Do not disconnect the line from the back of the gauge and run the engine. You'll be cleaning up oil from behind the dash for quite a while.)
Does the temp gauge have the 3-prong wiring harness connector firmly seated? If so, go to the driver's side of the engine and see if the single wire is attached to the small temp sensor screwed into the head between the 1st and 2nd spark plugs.
The door ajar light is controlled by the plunger switch at the very bottom of the door latch end of the door opening. Is it there and does it plunge OK? You can unscrew it and gently pull the switch out to be sure the wires are on the contacts and not touching each other. Takes maybe 2 minutes to pull and put back.
On the back of the oil gauge, is there a spaghetti sized plastic tube connected? That's the oil pressure line – it has a small bit of oil in it from the engine that presses on the mechanism at the rear of the gauge. (Do not disconnect the line from the back of the gauge and run the engine. You'll be cleaning up oil from behind the dash for quite a while.)
Does the temp gauge have the 3-prong wiring harness connector firmly seated? If so, go to the driver's side of the engine and see if the single wire is attached to the small temp sensor screwed into the head between the 1st and 2nd spark plugs.
The door ajar light is controlled by the plunger switch at the very bottom of the door latch end of the door opening. Is it there and does it plunge OK? You can unscrew it and gently pull the switch out to be sure the wires are on the contacts and not touching each other. Takes maybe 2 minutes to pull and put back.
Sounds like I need to get in behind the gauges....will do that as soon as it stops raining as I need to pull it out of the garage to get the passenger door open!
Le Mans Master
Joined: Aug 2006
Posts: 7,426
Likes: 1,559
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
