Need help please!!!

I had something similar happen to me. Replaced the voltage regulator 4 times before I found the problem. Turns out that the gas gauge would short to ground when I would hit a bad bump sometimes the gauges would peg and other times they would just die. Your car may be different, but on mine the Fuel, Oil and Temp all work off of the 5 volts that the instrument voltage regulator puts out. If one of the gauges shorts out it will put 12 volts on to the 5 volt circuit and peg or kill the other gauges and take out the regulator as well. I had checked for shorts initially and didn't find any, it was only when I wiggled the gas gauge did the short appear on the Ohm meter.

Good article tech article on the subject:

Hello CCTGENE,

Thank you so much for your reply.

We do have an OHM Meter, but my room mate can't figure out how to use it. Can you give me a short class?

Also, last night I talked to my brother-in-law, who is a mechanic in Minnesota and he said that maybe the circuit board is dead. However, today I called the Ford parts dealer and there is no circuit board available. Do you think the circuit board is the problem?

Hoping to hear from you soon.

Oceandog

You likely have a bad ground on the VR. If so, then the VR wont regulate and will put out 12v.

If you can get at the back without unhooking connectors, Set the meter to DC Volts, 25 volt scale; make sure probes are in proper locations to measure voltage. Red in Volt/ohm and black in com.

With red probe, measure the voltage on the three terminals compared to black probe on bodymetal ground:

If you dont see 0v on any of them, the ground path is broken.

There are still a lot of 79-86 mustangs in salvage yards

Hello Backyard Mechanic,

We have installed 3 different voltage regulators and none have worked.

Tomorrow we will do the volt check.

And what about the circuit board? Could that be the problem?

We have a place out here called Mustang Village, so are you saying I should install a new instrument cluster panel?

it's what I'd do... that plastic is not exactly top notch for longevity.

I think you can swap out the speedo assy if that's a concern... and remember to set the tach to the engine.

Also check your wiring grounds... that is what I was getting at... you may have brooken a wire in the harness

You mentioned that I may have a broken wire in the harness. Where exactly is the harness and how do we check for a broken wire?

And if you think I don't know what I'm doing, your 100% right.

Talked with Scott, who owns Mustang Village and he said he is more than willing to sell me gauges that I don't need.

He mentioned to check the grouond strap from the engine to the firewall. Can you explain what that means?

Thanks, Oceandog