Great Forum! I just spent the last two hours browsing through the posts...

I just bought a 1990 Eddie Bauer w/351 so that I can tow my toys (snowmobiles in winter and mastercraft p-star 190 in summer). Since this is a dedicated towing vehicle, I'm sure I will have many more questions and find myself in need of additional improvements for power and braking performance!

Hoping somebody has a 37 second answer to my immediate problem.

The trailer lights are very dim with the headlights on. When I activate a turn signal light, the signal works but it also alternates with the opposite turn signal light (both truck and trailer).

If I turn the headlights off, the signal light works at a rate faster than normal, although the opposite light does not come on in this situation.

Other electrical problems inherited with this beast include
1) Rear window defroster does not work, although the switch lights up when pushed.
2) Power door locks do not work from either driver or passenger side (fuse looks good from quick visual inspection)

I don't know if these problems are independent of each other or if there might be a single fix (yeah right!)...

By the way, I have checked the trailer and the lights work fine with my other vehicle. Also, I am using an adapter to allow a four flat trailer harness to work from the round ford harness.

I appreciate any light that can be shed on the problem.

 

The trailer lights are very dim with the headlights on. When I activate a turn signal light, the signal works but it also alternates with the opposite turn signal light (both truck and trailer).


Check your alt output when you have all the lights on. Sounds like you are not putting enuf out of the alt, may be starting to get weak. As far as making the other light blink you've got me there. Sometimes with a low power situation wierd things can happen... It'll blink fast if you haven't put in a heavy duty signal relay

 

For the defroster it most likely came unplugged in the tailgate with all the up and down over the years just pull the inside panel of and look for the loose wire and plug it back in to the bottom of the window. Also make sure you have checked the fuses in the engine bay, this is most often overlooked.

 

If you get an alternate flashing with the opposite turn signal lamps then the trailer is either reverse wired or one of the trailer lamps is being grounded due to reverse wiring. I take it you don't experience this without having the trailer hooked up. make sure that the sockets on the trailer are wired consistantly. In other words, the ground/neg should be the base of the lamp and the positive should be the contacts in the bottom of the lamp. If this is reversed, you will experience the type of problem you are seeing. What is happening is you are seeing a backfeed through a ground wire that is causing the other lmaps to alternate with the ones that are supposed to be flashing. Some cars deliberately have a side marker lamp set up this way so it flashes opposite the front turn signal lamp. A dead short to ground or even partial short to ground will cause the very dim operation as well.

Screwy is right on with the connectors for the defroster element on the window, the connectors are known for working loose over time. Hopefully you haven't lost the tab connector from the window surface.

The door lock thing sounds like someone didn't want their kids to be able to hit the door locks accidently. As there are no child safety locks on a two-door vehicle. So they had the power lock switches disconnected. Not certain on the 1990 model because my 92 has the buttons higher up on the door panels but I know mine have plug-in connectors at the back of the switch assemblies. My power mirrors didn't work when I first bought mine and that was the problem, the connector had come off the back of the switch assembly.

 

79_250RL, Screwy, and Greystreak, thanks for the input!

Results of playing around with the Bronco for an hour:
1) Trailer lights- Greystreak, you were dead on. The ground from the truck harness was not going to the trailer harness wire. The system was basically ungrounded. Geez, I thought these things were all standard, oops.

2) Rear defroster- Damn! Checked the leads into the window and they were plugged in. Took out the test light to see if there was any conductance across the window.. nope! Should have been obvious, but all the "metal line/heat stripes" had a worn out spot somewhere. Looks like it has been rubbing against something for a long time.

3) Power door locks- Didn't look into this too closely. I just changed out the speakers in the front doors about a month ago, and am counting on the fact that I am somewhat observant (which after the rear defrost incident I'm kinda doubting) to rule out that there was a disconnected lead. Checked the under-dash fuse and it was still good (it's shared with the power rear window, which works so I assume the power is at least getting to the fuse box). Still stumped on this one, but since this truck only gets driven once a week, not too worried about unlocking and locking manually. Although, if anyone has any further suggestions on this, I would be happy to investigate.

Thanks again for the help. I'll look forward to the day (or maybe not) when I can help the group out.