1965 Mustang Gauge Wiring Problem

by Arlie Robinson
(McKinney, Texas)

Question: My 1965 Mustang has 1966 instrument (gas,oil,amp,and temp) gauges.

I took it into a custom rod shop because the gauges did not work. Long story made short.

I spent $3,200 to have a Painless wiring harness and a new instrument voltage regulator installed.

I got just a few miles away from the shop and the gauges went dead again.

The rod shop said that I needed a stronger dash regulator. I have not been able to find anything to replace it.

Any help would be appreciated.

Answer: Ouch ! Two grand plus, to install a $ 600 wiring harness.

It's hard to diagnose an electrical issue without more discussion, but here's what I'd suggest.

I've never heard of having to use a "stronger" regulator. The stock regulator is the same piece for both the 65 and 66 cars and for cars with idiot lights or gauges.

You may have a short or an open in your gauge pod wiring, a blown fuse, a bad ground, a bad gauge voltage regulator, or the regulator is incorrectly wired.

Unless you have a digital volt-ohmmeter, or a friend who does, I'd be tempted to tell you to risk a new voltage regulator and see whether you have working gauges. But here's a way you can test the one on the gauge pod.

See if you can unscrew the gauge pod and pull it forward to reveal the wires. The regulator is the little metal box attached to the back of the panel. It's job is to convert the system's 12 volts to just 5 volts to power the gauges.

One wire is the 12 volt feed from the battery. There should also be a connection to ground and a voltage out wire. The voltage out wire should be sending a pulsing voltage (5 volts) to the gauges.

If you have no voltmeter you can still test it.

Turn the ignition on. You can test the output with a test light. You should have a pulsing light ( or pulsing voltage with a meter ).

If it's not pulsing, it's not working. Clean off the ground connection and try it again. If it's still no go, I'd try a new gauge voltage regulator.

It's unlikely, if not impossible that all the gauges are dead, so the source voltage or lack of it, is the problem.

Note: if the wiring to the gauges is still original, the color, should be black/green. You'll notice one of these wires to each gauge.

Comments for 1965 Mustang Gauge Wiring Problem

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1965 mustang gas gauge
by: Roger

i have a 65 Mustang and I am trying to hook up the original gas gauge.and i am haven problems. I don't know what.

Hi Roger.

I didn't get your whole message I think, so I'm going to take a guess from the above.

First off, I am assuming that you have the whole gauge, instrument bezel etc. I also assume that you have the gas tank, fuel sender in the tank and the original wiring. If that isn't the case, the procedure is going to be more tedious or expensive.

A few things have to happen in order for the original fuel gauge to work. You need to know that you have a good working sender/float assembly in the tank.

You need to ensure that the tank is making a good ground, which simply enough can be as easy as removing the original screws that attach the tank to the trunk pan and put them back in, which will make sure you have metal to metal contact.

Check the wiring from the electrical connector at the tank/sender which is a round fitting at the rear of the tank with a hose connection to the fuel line and a spade connector to the fuel sender wire.

Make sure that the wire from the tank to the gauge is not grounding out or cut. An easy way to check is to connect an ohmmeter to either end to verify continuity.

That being ok, you then need to ensure that you have power to the sender, and ground. Finally, you need to verify that the gauge itself works. Old Mustangs tend to have a lot of rust and corrosion in and around the wiring and especially the ground contacts.

Clean all of them up to ensure good electrical contact and test the gauge.

The last item, I think, is what I should have recommended first. Get a decent Mustang repair manual, with the wiring diagrams for your 65 Mustang (the colors of the wires can otherwise be similar but different)and follow each wire and it's color from beginning to end.

Good Luck!

by: 4 Aces

I decided to convert to a single wire altenator and now the charging system is working fine. I installed a voltmeter instead. Thanks for the feed back.

alternator. charging issue
by: 4 aces

I have a 65 ragtop C code 289 v8 and the alternator checks good but isn't charging the battery.

I've replaced the regulator. The amp meter isn't registering and ohms out as open. Manual says the voltage comes from the ignition through the amp gauge to the regulator. Can a bad gauge open the charging circuit?
4 aces
jlaccor at msn dot com

Note: changed your email addy. Don't want to risk spamming. (B.)

In answer to your question. Yes, an open in the gauge can prevent power transferred through it. (think cutting your garden hose in half with the water running).

Try making the circuit completer without the ammeter and see what happens. Also, check to make sure that your wiring to the regulator is where it is supposed to be attached.

Good Luck!


by: Anonymous

When testing the wiring on a 1965 Mustang oil Gauge, should your gauges be pulsing when I do the test or just the amp gauge ?

Please respond, thank you.


The 1965 Mustang oil Gauge and any others should not show a pulsing voltage. An amp gauge or ammeter shows you the output of your alternator or generator (depending on whether you have an early car or a later built one).

If you have pulsing voltage, or a pulsing output on your gauges, then I would suggest that you check the little metal constant voltage regulator, which is attached to the back of the gauge cluster. It's a small rectangular metal box with two metal posts sticking out and a wire attached to either end.

1965 Mustang oil gauge voltage regulator

This little box regulates the pulsing voltage that comes from an alternator or regulator for not only the 1965 Mustang oil gauge, but all of the gauges and in effect, evens out the current into a smoother direct current (dc).

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