Dash lights/radio lights stay on with key off and with fuses out.

[KSousa]

I'm new here and new to the Foxbody scene.
I've searched the forums for this issue and either don't understand the answers or have not seen these specific symptoms.
I have a 1990 here in the shop and the dash lights will not go off no matter what I do.
I specifically pulled fuse #4 and fuse #13 and the lights stay on.
I then sequentially pulled every fuse out of the fuse block and the lights stayed on.
I've flipped the headlight switch on and off a multitude of times. The exterior running lights and headlights work just fine.
There's certainly enough draw here that it drains the battery overnight.

I've seen references to SJB but am new enough to these that I don't know what that is, where it is, or what it does.

Would anyone have similar experiences and solutions?

thanks

 

[Mustang5L5]

Pulling the fuse 13 or 4 should kill the dash lights completely.

The fact that they stay on makes me wonder if someone did some "custom wiring" at some point.

 

[Mustang5L5]

Here’s the wiring diagram if you don’t gave it

 

[NXcoupe]

I'm new here and new to the Foxbody scene.
I've searched the forums for this issue and either don't understand the answers or have not seen these specific symptoms.
I have a 1990 here in the shop and the dash lights will not go off no matter what I do.
I specifically pulled fuse #4 and fuse #13 and the lights stay on.
I then sequentially pulled every fuse out of the fuse block and the lights stayed on.
I've flipped the headlight switch on and off a multitude of times. The exterior running lights and headlights work just fine.
There's certainly enough draw here that it drains the battery overnight.

I've seen references to SJB but am new enough to these that I don't know what that is, where it is, or what it does.

Would anyone have similar experiences and solutions?

thanks

So this isn't your car? What was the last thing the customer did to the car? I've seen car alarms do stupid crap like this, but if the harness has gotten hot and a power wire melted to the dash light wires,this could happen. I'd continue pulling fuses and unhooking fusable links until the lights go off. That will tell you what circuit is suspect for powering these.

 

[KSousa]

Not my car. Customer tells me that there is an aftermarket alarm system in it but that the alarm never interacted with the interior lights, just exterior lights. I've pulled enough of the dash apart to find the alarm hardware. I've pulled the inline fuse out of the alarm and the interior lights still stay on.

I have yet to find any fuse or anything that will kill these lights short of pulling the battery cable.
I'm thinking I'm now in a hunt to try and trace a light blue wire with red stripe from the fuse box to wherever it leads. The schematic shows that wire feeding power to the interior lights, but only after #13 fuse, which I've pulled. Perhaps it's shorted against a different power wire as suggested.

 

[Mustang5L5]

Interior and exterior lights do tie together at the instrument panel dimmer. Wire 14 at the headlight switch feeds the dimmer which jumps to the exterior lights. The Brown wire (wire 14) is the feed and the Light blue/red wire is your interior lighting circuit (wire 19)

Pulling fuse 13 should completely isolate the interior light circuit. You should not have 12V+ to ground on wire 19 at this point.

If you pull fuse 13 and activate the alarm. Do the exterior lights blink? If so, that means the alarm is tied into wire 14 and is probably not the issue.

If the exterior lights do NOT blink, unless fuse 13 is in place, than that means they tied the alarm wire into wire 19 which was backfeeding to blink the exterior lights. That also means the interior lights DID flash with the exterior lamps.

With fuse 13 pulled, wire 19 is 100% isolated from power and there is no way to light up the interior lights unless an change was made to the system, in which the suspect is the alarm.

Wire 19 is getting 12V by something that should not be there.


Another possibility is that one of the connectors downstream of fuse 13 on wire 19 got switched around. I've seen this happen, especially on the defrost switch, where the pins get pulled out and someone puts them back incorrectly and feeds 12V where it shouldn't go. You might want to unplug those various items and see if you still have 12+ on the Light Blue/Red stripe wire.