What's causing faulty brake light circuit on 1997 Ford Club Wagon?

JOLISSA

MEMBER
1997 FORD E-SERIES VAN
248,000 MILES

I’ve inherited a 1997 Ford Club Wagon XLT with at least one electrical problem. The problem is manifested in no brake lights (vehicle does not electronically know when it is braking), the left turn circuit not working, and fuse 10 (headlamp switch, multi-function switch) blowing when the headlamp switch is turned to park or headlight. In addition to this fuse 11 (brake switch, brake pressure switch, multi-function switch) used to blow when I stepped on the brake with the old brake switch installed. The hazard circuit appears to only work with the front lights.

Abuse the vehicle has been through: the guy I got it from installed the battery the wrong way. In addition to this both fuse 10 (20A) and 11 (15A) were replaced with higher rated fuses to keep them from blowing, I think possibly up to 30A fuses. This allowed him to drive it without the brake lights going out from a blown 11 fuse.

What I’ve tried. The vehicle now has a new alternator, primary battery, brake switch, brake pressure switch (& plug), and fuses. I’ve checked continuity for the full length of the brake circuit and it looks good. I have tested both the multi-function switch and the headlamp switch. I’ve plugged in a code reader to find no DLC’s. I’ve checked for the appropriate voltage at the brake switch plug. I’ve checked every fuse and fusible link, as well as partially tested the PCM relay. Finally I’ve checked right & left back bulbs.

The vehicle is equipped with what looks to be aftermarket trailer brakes and an auxiliary battery. Probably an unrelated problem but I found out that both the 20 (electric brake controller) and 22 (trailer battery charge) fuses in the engine bay were blown, so I replaced those as well. I do not know what’s wrong. PCM? Thanks for any ideas or help!

1 Reply

CARADIODOC

MECHANIC
33,873 POSTS

Start with checking the trailer connector wiring. Often they get chewed up from scraping on stuff near the hitch.

There's a good chance when you find the cause of one blowing fuse, you'll find others in the same area. That is typical with multiple blowing fuses. Look for wire harnesses that fell down onto hot exhaust parts, and harnesses that are rubbing over sharp edges of brackets.

To prevent popping more fuses, pick one circuit to start with and replace that fuse with a pair of spade terminals, then use a pair of small jumper wires to connect them to a 12 volt light bulb. The bulb will limit current to a safe value. When the circuit is powered up and the short is present, the bulb will be full brightness and hot so don't let it rest on carpeting or against plastic door panels. Now you can move stuff around and unplug various connectors and computers to see what makes the short go away. When it does, the bulb will get dim or go out.