FYI FORD MustangSteve's Ford Mustang Forum / Electrical issue in my 68 Cougar.

**Posted by BTaylor** 5/23/2024 2:35 PM

Just replaced my ignition switch in my 68 Cougar. Now I have an electrical issue with gauges, believe I have a short.
My oil gauge is pegged out and my amp gauge is -60 with the ignition on. More curious is my low fuel light is on without the ignition on and it is not even connected at the tank.
Im sure I have an issue under the dash but can anyone narrow possibilities before I go under there. I have a bad back that limits movement or time under there.
Thanks

**Posted by MS** 5/23/2024 3:45 PM

Backtrack what you did. You will find it. Did you MODIFY it or just replace the switch?😈

**Posted by BobE** 5/24/2024 5:00 AM

MS wrote:
Backtrack what you did. You will find it. Did you MODIFY it or just replace the switch?😈

Agree w/MS. I'll add to disconnect the new ignition switch and see if the condition goes away. Or, try re-installing the old switch and see if the condition goes away. I'm not sure how, but the new switch may have an internal issue.

**Posted by BTaylor** 5/24/2024 6:56 PM

Tested new switch and it is good, bought a second switch and installed. The gauges are still pegged out.
Went under looking for exposed or pinched wires, nothing. Resorted to leaving the ignition on and just grabbing and wiggling wires under the dash I could reach. No change.

**Posted by BobE** 5/25/2024 5:43 AM

I'd still suggest installing the old switch and see if the problem disappears. Maybe the new switches are not the same as the old switch.

**Posted by 6sally6** 5/25/2024 10:22 AM

OR.........dis-connect each wire and see if that makes a change.
By re-installing the old switch.....IF everything goes bad to normal that will tell you "hey I didn't screw something up...it must be the 'new' part.."
6sal6

**Posted by Mach1Driver** 5/25/2024 5:00 PM

The temp, oil and fuel are all together in one circuit, that is unrelated to the ammeter, except that they get power when the ignition switch is turned on. If the oil is affected, then the fuel and temp should be also, so your symptoms are strange. It sounds like two separate problems, or some sort of short.
Is the ammeter near the oil gauge on a 68 Cougar? Could there be a short between the two? This year doesn't have a flex circuit for the dash does it?
For the ammeter discharge, I would would disconnect the plug to the voltage regulator, turn the ignition to ON (don't start it) and see if you still have the 60 amp discharge. If that doesn't help, disconnect the B+ wire to the alternator and try again. Good luck, keep us posted.

**Posted by BTaylor** 5/26/2024 10:09 AM

I have resolved the issue with the amp gauge. But the oil gauge is still grounded. Next step to to pull the dash and chase the sender lead. Also have a couple extra oil gauges I will check to be sure the issue is not in the gauges itself.

**Posted by MS** 5/26/2024 1:17 PM

Gauge pegged is usually a ground issue. As previously stated, Oil, Temp and Fuel ate on same power wire.
Check the offending gauge to be sure it is properly mounted in the gauge cluster. If a stud is touching metal, there is your problem. It should have insulators on both studs. A hot side problem would likely affect all three gauges the same.

**Posted by Mach1Driver** 5/26/2024 1:26 PM

The gauge has a bi-metal that bends when heated. The heater wire is the only thing electrical about the gauge, and has a resistance in the range of 16-18 ohms for 68 and older cars. The IVR (instrument voltage regulator) pulses 12v to give an average of 5v. That goes to the gauge, and then from there to the sender which has a resistance value of 10 ohms on high to 73 ohms on low, and that connects to chassis ground. That's all there is- the IVR, gauge, and sender. If the water and fuel work, you know the IVR is OK.

Last edited by Mach1Driver (5/26/2024 1:41 PM)

**Posted by BTaylor** 5/28/2024 3:26 PM

Mach1Driver wrote:
The gauge has a bi-metal that bends when heated. The heater wire is the only thing electrical about the gauge, and has a resistance in the range of 16-18 ohms for 68 and older cars. The IVR (instrument voltage regulator) pulses 12v to give an average of 5v. That goes to the gauge, and then from there to the sender which has a resistance value of 10 ohms on high to 73 ohms on low, and that connects to chassis ground. That's all there is- the IVR, gauge, and sender. If the water and fuel work, you know the IVR is OK.

Thanks, this will give me what I need to test it.