[89supercharged]

Hi all
got a hopefully small electrical problem hoping for some help.
Everytime I turn my headlights on the fuse blows at first I would have to turn the headlight switch on the install the switch but I would have no cluster lights now the fuse keeps blowingthe car is a 1989 mustang gt.
any thoughts?

 

[crjackson]

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[Cobrajet67]

Hi all
got a hopefully small electrical problem hoping for some help.
Everytime I turn my headlights on the fuse blows at first I would have to turn the headlight switch on the install the switch but I would have no cluster lights now the fuse keeps blowingthe car is a 1989 mustang gt.
any thoughts?

I have no idea what "on the install the switch" means. You're going to have to reword whatever it is that you're trying to explain. When/if you do then use punctuation as well.
1987-93 Mustang fuse panel diagram:

 

[89supercharged]

I have no idea what "on the install the switch" means. You're going to have to reword whatever it is that you're trying to explain. When/if you do then use punctuation as well. 1987-93 Mustang fuse panel diagram: View attachment 793579 View attachment 793579

Sorry about that I meant to say turn the headlight switch on then install the fuse(#4 on the diagram) now the fuse just keeps blowing each time I go to turn the lights on

 

[Cobrajet67]

Explain again about what was happening with the cluster lights. Proofread it please.
You can have a problem anywhere in any of the circuits for the headlamps, taillamps, parking lamps, side marker lamps, instrument clusters illumination lamps, or license plate lamps.

 

[89supercharged]

So the #4 fuse keeps blowing I disconnected the battery then installed a fuse it blew without turning the headlight switch I took a picture of the headlight harness and this is what I saw.
Do I need a new harness?

 

[Cobrajet67]

So the #4 fuse keeps blowing I disconnected the battery then installed a fuse it blew without turning the headlight switch I took a picture of the headlight harness and this is what I saw.
Do I need a new harness?
View attachment 793775

So what was happening with the cluster lights?
Were the cluster lights not working and then gradually the lighting circuit fuse started blowing?
If so, then I would assume that the problem is with the cluster lights. Maybe the cause is a cluster voltage regulator, cluster lights, or other interior lighting.
My headlight harness was actually melted and it didn't blow fuses so I would say that yours is just probably showing some signs of heat from long use. Ford seems to have underengineered much of the electrical systems in the fox body Mustangs and other Ford cars of the era. There were actually recalls for the ignition switches.
I would unplug as much of the lighting system as possible including the headlight switch, dimmer, and all exterior light sockets and then put a fresh fuse in. If it doesn't blow immediately then you know that it's something that you unplugged. You then plug one lighting item in at a time and monitor the fuse. Once the fuse blows then you found the culprit and you can then scrutinize that particular circuit route for issues.

 

[89supercharged]

Great advice I will try that and see how it goes I very much appreciate your help and patience as for the cluster lights yes you are correct they were not working and gradually the circuit fuse started blowing then just got worse overtime.Now like I mentioned the fuse just blows as soon as I install it with nothing turned on.I have also read that often the dimmer switch needs to be replace but I will start with just unplugging everything the picture I sent you was with the gauge cluster removed from the car.
Thank you.

 

[Cobrajet67]

Great advice I will try that and see how it goes I very much appreciate your help and patience as for the cluster lights yes you are correct they were not working and gradually the circuit fuse started blowing then just got worse overtime.Now like I mentioned the fuse just blows as soon as I install it with nothing turned on.I have also read that often the dimmer switch needs to be replace but I will start with just unplugging everything the picture I sent you was with the gauge cluster removed from the car.
Thank you.

I would suspect something that's involved with the cluster lighting. Try unplugging the dimmer switch, headlight switch, and the cluster lighting harness first.

 

[89supercharged]

Good morning so I unplugged everything that the #4 fuse is running I installed a new fuse and it didn't blow which I thought was great news then without the headlight switch turned on the cluster lights lit up(WTF) here are some pics the first one is is with the switch in the off position the second is the switch in the first position and the third is with the switch fully engaged.
So I think my car is possessed and is driving me a little crazy.

 

[Cobrajet67]

Good morning so I unplugged everything that the #4 fuse is running I installed a new fuse and it didn't blow which I thought was great news then without the headlight switch turned on the cluster lights lit up(WTF) here are some pics the first one is is with the switch in the off position the second is the switch in the first position and the third is with the switch fully engaged.
So I think my car is possessed and is driving me a little crazy.

Listen, you have to proofread before posting and use punctuation. I can't understand much of what you write. Please edit this post.

 

[89supercharged]

Sorry I will try it this way and make it shorter.
I unplugged everything the #4 fuse ran.
Installed a new fuse.
Plugged in the cluster harness and it lit up with the headlight switch in the off position(pic#1)
2nd pic is the headlight switch is the headlight switch in the 1st position
3rd pic is the headlight switch fully engaged to turn on the headlights.
I hope that explanation is better.
Thank you.

 

[Cobrajet67]

Have you done a lighting mod to your cluster lights? They're red.
Did you unplug all the relevant exterior bulbs on that circuit too?
Also, I see aftermarket gauges run.
If there's any sort of different bulbs in the cluster then they may be the problem or the aftermarket gauges may be causing a problem. If any exterior bulbs are still plugged in then any of those or the sockets could be the problem too.
UnpIug all exterior sockets or bulbs and then unplug the cluster lights and then the aftermarket gauges. If the other interior lights like heater controls stay steady with the headlight switch turned on then one of those are the issue. If so, starting with the cluster, plug it in and then go one by one with the exterior bulbs until you see the interior lights dim with the headlight switch on.
You could always buy a new headlight switch or dimmer switch and see if that makes a difference.

 

[89supercharged]

Thanks again for the help the problem was happening before the mod lighting and the aftermarket gauges all exterior bulbs on that circuit were unplugged before I plugged in the cluster lights.I will go ahead with your advice and hopefully I will find the cause.
Thank you

Would the instrument cluster lights come on if the dimmer switch is unplugged?

 

[Krem12]

Would the instrument cluster lights come on if the dimmer switch is unplugged?

Dont believe so. All power for internal lights seems to be ran through that switch and then to the fuse panel. Circuit 19 on a 1990. Switch also powers a relay that kicks over all the other internal LED's to their dim setting.

 

[Cobrajet67]

Dont believe so. All power for internal lights seems to be ran through that switch and then to the fuse panel. Circuit 19 on a 1990. Switch also powers a relay that kicks over all the other internal LED's to their dim setting.

When you say relay do you mean voltage regulator and also by LEDs I think you meant bulbs?

 

[89supercharged]

So I found the short that was blowing the fuse it was one of the wires in the tail lights which was a relief.
Now the parking lights, tail lights and cluster lights stay on when the headlight switch is off I going to change the headlight switch then the wiring harness and see if that fixes the problem other wise I will just have to keep removing the fuse not sure what else to do.

I also read that the turn signal switch could cause some issues not sure if that's true.

 

[Krem12]

When you say relay do you mean voltage regulator and also by LEDs I think you meant bulbs?

No there's a relay that the dimmer switch powers a relay coil. Controls the brightness on radio, a/c and other interior let's. Lights off your radio etc gets full 12volts from a circuit. Lights on its powered from a reduced voltage circuit powered through the dimmer switch.

The dash itself is powered directly from the dimmer switch. I'll post the wiring diagram later . Will be helpful for OP anyways

 

[Cobrajet67]

So I found the short that was blowing the fuse it was one of the wires in the tail lights which was a relief.
Now the parking lights, tail lights and cluster lights stay on when the headlight switch is off I going to change the headlight switch then the wiring harness and see if that fixes the problem other wise I will just have to keep removing the fuse not sure what else to do.
View attachment 793902 View attachment 793903

I also read that the turn signal switch could cause some issues not sure if that's true.

You hadn't mentioned before that you had aftermarket lights which is very relevant here. Aftermarket electrical parts are often the cause for problems. None of that stuff is made with the same quality or care as original parts are. They're also LED which you should have mentioned too.
The short for the aftermarket lights may have damaged the headlight switch or caused other damage to the wiring or connector that feeds it from the main power source from the fuse box. Everything up to and including the fuse box would be suspect.
It might be that only the high beams may go thru the turn signal switch but idk for sure. If that's the case, then it wouldn't affect the rest of the lights that you said are staying on. If the rest of the wiring goes thru the turn signal switch then it could be the connector, wiring, or maybe the switch as well. Perhaps Krem12 has a diagram that includes that too that he can post.

 

[Krem12]