Resource icon

'87-'93 GT Fog Lamp & Main Light Switch Fix 2018-08-10

No permission to download
Model
Ford Mustang GT '87-'93
Engine
5.0
Main Light & Fog Lamp Switches - only affects GT's.

In the February, 1991 edition of Popular Mechanics, the "Car Clinic" by Mike Allen had the following:
Fogged Out
Q: "I have a 1988 Ford Mustang GT. After about 20 minutes with my headlights and fog lights on at the same time, the headlights blink intermittently."

A: "I rarely find the answer to a Car Clinic problem covered in a TSB, but every now and then...
Ford TSB 89-17-11 says this is caused by overheating in the headlamp circuit. It's a phenomenon affecting '83-'89 Escorts, '83-'87 EXPs and '87-'88 Mustangs. You'll need to replace the headlamp and dimmer switches, several connectors, and then bypass the wiring in the circuit with new 12ga wire run alongside the original harness. It's supposed to take 1.3 hours for a service technician to do this, and you ought to see if the dealer will still do the repair under warranty."

I recently changed this circuit so the fog lamp circuit is independent of the main lamp switch, no rewiring of any kind is required. This will eliminate the overheating condition.

I was helping someone diagnose this & all of a sudden it just came to me how simple this would be. Only an add-a fuse plugged in the right way in the fuse box. I then added DRL's to the circuit because the LED fog lamp bulbs were not very bright.

There is a recent YouTube video but the guy didn't understand when I tried to explain to him that the orientation of the add-a fuse is important. Otherwise, you have one fuse feeding another & then to the load. His fuse box was all messed up, mounted upside down, looked all wrong. He blew me off in not a very nice way.

I did the cutouts years ago for cooling. GT's had reduced cooling, all airflow to radiator comes from under the nose. That's why '93 Cobras had a different grille.
IMG_0751.JPG



Here's the fog lamp fix to enable them to function independently of the headlights.
Add-a-circuit goes into #16 (20A-yellow), red pigtail connects to load (left) side of #15 (15A-blue).
Pigtail comes with a butt splice, cut it off & crimp a spade connector on.
#12 is pointing to the empty position below. #15 has an arrow pointing to the position above it.
#15 is only for the Fog Lamps & nothing else.

s-l1600-1.jpg
BTW, didn't have to use #16, but wanted something on the same 12V bus bar as the headlights (#4) or #8.
4, 8, 16 are fed from the same 12V bus, all fed by Fuselink B.
The problems with 4 & 8 was clearance for the add-a-circuit & the fuse panel cover.
You can see that #4 is in the lower left corner. That was the perfect one until I tried to put the cover back on.
Actually, #16 is better because you can tell which fuse is which by the color.
Fog Lamp Circuit Fix.JPG
Author
Blown88GT
Downloads
0
First release
Last update
Rating
0.00 star(s) 0 ratings