Foxbody Electrical Fire Please Help

Fuse 8 should be for the courtesy lamps, glove box lamps, vanity lamps, cargo, engine compartment light, ect. Sounds like you have a short in the wiring somewhere going to one or more of these accessories. Since these accessories are all throughout the vehicle, unless you replaced the entire vehicle's electrical harness and switches you might not have found/replaced the issue.

Here is a wiring diagram for an 87-93 mustang. You are looking for all the accessories toward the middle/bottom that have the "LT GRN - YEL" wiring connected to them. You can see toward the bottom right where it says "Glove Box LT" that the "LT GRN - YEL" wiring is connected to fuse #8.




To troubleshoot, you will need to test all this wiring coming from fuse #8 at each connection point to figure out where it is shorted to ground. You can also disconnect each accessory that is connected to fuse #8, put a good fuse back in and see if the fuse blows. If it does, you know its in the wiring. If it doesn't, then there is something wrong at one of the accessories, then you can test each accessory one by one. I usually use a test light to test the circuit each time I plug something in so I don't have to keep going back to check the fuse. It could be a pinched/shorted wire, a bad switch, or something else.

You can also check the gray/yellow wiring coming from the ignition switch to fuse #8 for any shorts/bare wire as this would blow the fuse.

I've heard of a couple people that have had this issue and it was the wiring going to the map lights/vanity lights. Usually the wiring to the map light breaks where it bends and shorts out. Might be one of the first areas you want to check.