Topic: Temp gauge not working HELP!

[Crgjohnson]

Hi everyone,
I'm having issues with my engine temperature gauge not working on my 69 Cougar with a 351W 2bbl, Here is a rundown of what I have already tried and the components.

Fuse box there were no blown or missing fuses
Engine feed wire harness is new
Under dash harness is original with everything working except the temp gauge. The gauge worked prior to disassembly. I verified that the electrical connection that plugs into the cluster was fully seated, Also verified that the actual contact connections in the plug were free of damage and corrosion.
Instrument cluster is original including the circuit board
 Constant Voltage regulator is original. At the sender wire connector I did not have a flashing light on my tester which should mean the CVR is not sending a signal. However, the fuel gauge works which should means the CVR is sending signals. I disconnected the engine feed harness at the fire wall connection and still did not get a flashing light on my tester
Sending unit Replaced with known good unit
Fuel gauge did not peg when wire at sending unit was grounded, I also verified that the gauge was not grounding in the instrument cluster housing
Block to fire wall ground is attached and tight. All under dash grounds are attached and tight

 Based on my troubleshooting I'm leaning towards either a bad wire between the firewall and gauge or a bad cluster circuit board
Did I miss something? I would love some wisdom on this if possible

Best regards,

Craig

[KevinK]

I believe I saw something recently about an inline adapter wire used on the 351. I never heard of this before nor could imagine why it would be needed. Someone did point it out and I believe it was labeled for 351.

[midlife]

I think your fuel gauge is not properly seated in the dash cluster.  This is hard to do correctly.  Basically, one of the posts of the gauge is touching the metal dash cluster housing on the back side, which is impossible to see under the insulating pad, the circuit card, and the nut.  You can test this hypothesis by measuring the resistance between one of the fuel posts and the metal dash cluster housing: it will read 0 or 14 ohms (depending upon which post is contacting metal).  If so, re-position the gauge so that both posts read well above a kilo-ohm.  You can also wrap black electrical tape around the rectangular metal cut-out where the posts go through to prevent this problem.

[Crgjohnson]

Hi Kevin. The small harness extender is for 351’s built after 3/69. It was a TSB that directed this. Thanks for the input

Hi Randy. I will put a multi meter on it tomorrow and see if it’s the actual gauge shorting out on the housing. Thank you

Craig

[Bob Gaines]

Hi everyone,
I'm having issues with my engine temperature gauge not working on my 69 Cougar with a 351W 2bbl, Here is a rundown of what I have already tried and the components.

Fuse box there were no blown or missing fuses
Engine feed wire harness is new
Under dash harness is original with everything working except the temp gauge. The gauge worked prior to disassembly. I verified that the electrical connection that plugs into the cluster was fully seated, Also verified that the actual contact connections in the plug were free of damage and corrosion.
Instrument cluster is original including the circuit board
 Constant Voltage regulator is original. At the sender wire connector I did not have a flashing light on my tester which should mean the CVR is not sending a signal. However, the fuel gauge works which should means the CVR is sending signals. I disconnected the engine feed harness at the fire wall connection and still did not get a flashing light on my tester
Sending unit Replaced with known good unit
Fuel gauge did not peg when wire at sending unit was grounded, I also verified that the gauge was not grounding in the instrument cluster housing
Block to fire wall ground is attached and tight. All under dash grounds are attached and tight

 Based on my troubleshooting I'm leaning towards either a bad wire between the firewall and gauge or a bad cluster circuit board
Did I miss something? I would love some wisdom on this if possible

Best regards,

Craig

Given it worked before disassembly as you indicated I think reply #2 is logical.

[Crgjohnson]

I figured out what the issue was with the inoperative temp gauge. After verifying that the wire from the cluster and the firewall connector was good, the gauge posts were not grounding on the cluster housing I also rechecked the copper connector on the circuit board where it plugs into the harness. I discovered that the circuit board at the connector had very slightly folded over on itself. Once I carefully flattened out the connection I received a pulse on my tester at the sender connection and the gauge started reading.

Thank you Randy, Kevin and Charles for taking the time ti give me advice. It is appreciated

Craig

[midlife]

Dang.  My record now goes to 10 out of 18,758 with correct diagnoses...
Glad you got it resolved!

[Crgjohnson]

https://i.imgur.com/oUBruUZ.jpg