1984 Mustang - Wiring issues - Any suggestions would be appreciated

mercury-man · Apr 18, 2022

I have a very original 1984 Mustang 5.0 that has several issues:
1. Dash lights don't work
2. Temp gauge and Amp gauge don't register
3. Windshield Wipers don't work (they do work if they are jumpered).

When I look under the dash, I see several connectors that are not attached (see pictures below). The question marks on the connectors were already there. I also see what I think is some wiring that has been added.

The prior owner added air conditioning and I have to wonder if the wiring issues are the result of the air conditioning being added. The air conditioning was added to look like factory air. Incidentally, the air does not blow cold.

Any thoughts or suggestions would be most appreciated. Or am I dealing with a hornet's next that has no easy solution. Or does the car need to be completely re-wired?

General karthief · Apr 19, 2022

First question would be is this a V8 conversion?

mercury-man · Apr 19, 2022

Except for the a/c, the car is very original. Being a notchback 5.0 with 5-speed transmission, it is a rare car.

There are also some disconnected wires under the hood.

Here is a description of the car, from 2017, before the a/c was added:

limp · Apr 19, 2022

I am redoing some of the wiring under the hood in my 83... It was a survivor too, but some of the wiring is cracked and brittle while some of its in great condition.. Rebuilding the engine harness as NONE are available........
Beautiful car.......

mercury-man · Apr 19, 2022

My wiring all seems to be pretty good. In so many ways, the car is a remarkable survivor.

But it is a mystery as to why all the connectors aren't plugged to something.

Mustang5L5 · Apr 19, 2022

Those look like relay connections.

Keep in mind, Ford tried to make as few combinations of harnesses easy year as they could. So there might be one or two dash harnesses covering 6 or 7 models and engine types. For example, a lot of the connectors for the convertible top relays are present on hardtops, but just left empty. On the 87+ cars, the 2.3L fan controller plug is a very common plug that people always ask "what does this go to?"

So it's entirely possible those plugs do not connect to anything because they are not needed for your model.

I would highly recommend a 1984 EVTM which may help troubleshoot your issues.

Pardon Our Interruption...

for the inop dash lights have you checked the fuse? I believe there is a 5am fuse just for those.

mercury-man · Apr 19, 2022

Thanks very much for the recommendation on the Shop Manual. I have purchased it.

And thanks for your thoughts about the possibility that a lot of the un-attached connectors may not be needed. Whoever put the question marks on the disconnected connectors was probably like me and did not understand that they might not be needed.

I will check the dash light fuse.

I also notice that the windshield wipers have a 6 amp circuit breaker (#2) so I will do some research on that. I suppose it is possible that the circuit breaker has gone bad????

The temp gauge definitely does not register. And the Amp gauge needle never moves from the center position so I don't think it works. I suppose both gauges could be bad, but, since they appear to be on the same circuit, I suspect that something isn't properly. connected.

General karthief · Apr 19, 2022

Time for a test light and a digital volt meter.

mercury-man · Apr 19, 2022

I am a duffer of a mechanic. I have a volt meter, but no test light. But I would need to study some youtube videos on how to begin to test a wiring circuit.

I should have learned to be a better mechanic when I was younger (I will be 86 this year). But my interest was always in detailing and polishing and making the cars look good.

I am going to check the dash light fuse and also pull the windshield wiper circuit breaker and take it to a parts store to be tested.

mercury-man · Apr 19, 2022

OK, the dash light fuse was blown. I installed a new fuse, turned on the lights the new fuse instantly blew, so there has to be a shoirt shomewhere. But, for me, finding it will be a challenge.

I also took the windshield wiper circuit breaker to O'Reilleys but they said that they had no way to test it.

limp · Apr 19, 2022

mercury-man said:
OK, the dash light fuse was blown. I installed a new fuse, turned on the lights the new fuse instantly blew, so there has to be a shoirt shomewhere. But, for me, finding it will be a challenge.

Your one step closer to fixing it.......

mercury-man · Apr 19, 2022

Could the problem with my dash lights possibly be the light switch? All the exterior lights come on and, when I rotate the light switch until it clicks, the interior overhead light comes on. Or is it more likely to be a bare wire?

As previously mentioned, I took my windshield wiper circuit breaker (6 amp, part number D9ZB14526-AA) to O'Reilleys and they said that they had no way to test it. Can anyone suggest a parts store that could test my circuit breaker?

General karthief · Apr 19, 2022

You should be able to test a breaker with a test light or DVM. Set one prong of the breaker on the positive terminal of the battery and touch a test light probe to the other (ground side of test light on battery ground).
Similar with a DVM.
Pull the instrument cluster out, with the connector for the lights unplugged, install a good fuse, if it blows then the problem is in the wires, if not it will be the print board on the cluster.
You can do the same test with the switch. Maybe start with the switch 'cause the power through the switch before the cluster.

mercury-man · Apr 19, 2022

As previously mentioned, I am not much of a mechanic. I do have multi-meter so I will see if I can figure out how to test the circuit breaker.

Thanks, appreciate the suggestions.

General karthief · Apr 20, 2022

Googlefu is your friend.
I wouldn't appear as experienced and knowledgeable without it.

mercury-man · May 29, 2022

Finally found a good shop that was able to fairly quickly fix the electrical issues with my Mustang. Dash lights. windshield wipers and washers and amp and temp gauges now work.

89notchDude · May 29, 2022

mercury-man said:
Finally found a good shop that was able to fairly quickly fix the electrical issues with my Mustang. Dash lights. windshield wipers and washers and amp and temp gauges now work.

So what was the fix?

mercury-man · May 29, 2022

They had to completely dismantle the dash To find and fix the problems.

Several problems were apparently created when the a/c and the aftermarket radio was installed.

It turned out that the under dash wiring to the wiper stalk had been left dis-connected.

The temp sending unit had to be replaced. The dash lights had a short (some bare wires and a problem with the radio wiring). The amp gauge started working after everything was put back together so something they did in re-arranging and correcting the routing of under dash wiring apparently fixed the amp gauge.

As someone commented earlier, most of the unplugged connectors were for features that my car doesn’t have.

I had to hunt long and hard to find a shop that would take on my car. Luckily, the shop I finally found took a real interest in helping me. A big plus, they were reasonable and less than two miles from my house.

89notchDude · May 29, 2022

mercury-man said:
They had to completely dismantle the dash To find and fix the problems.

Several problems were apparently created when the a/c and the aftermarket radio was installed.

It turned out that the under dash wiring to the wiper stalk had been left dis-connected.

The temp sending unit had to be replaced. The dash lights had a short (some bare wires and a problem with the radio wiring). The amp gauge started working after everything was put back together so something they did in re-arranging and correcting the routing of under dash wiring apparently fixed the amp gauge.

As someone commented earlier, most of the unplugged connectors were for features that my car doesn’t have.

I had to hunt long and hard to find a shop that would take on my car. Luckily, the shop I finally found took a real interest in helping me. A big plus, they were reasonable and less than two miles from my house.

good to hear... sounds like a good shop....

mercury-man · May 30, 2022

Yes, I was impressed. Here is their bill:

1984 Mustang - Wiring issues - Any suggestions would be appreciated

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wonder how much it would cost to ship you a pair

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wrap a little cheese around it and its a done

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That is…until I whipped out my Bissell

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wonder how much it would cost to ship you a pair

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wrap a little cheese around it and its a done

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wonder how much it would cost to ship you a pair

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wonder how much it would cost to ship you a pair

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