Trailer lights screwy.

[oldyellr]

My son's 1998 Ranger had a trailer hitch ball on the bumper when he bought it recently, but no trailer wiring plug. We discovered it had been cut off and taped up behind the bumper.

I found the cut off cable had 4 wires inside, which we identified as follows:

Green - ground
Dark with white stripe - taillights
Yellow - left flasher
Dark brown - Right flasher

(The "dark" and "dark brown" are guesses due to poor lighting and eyesight, but they couldn't be confused with any of the others anyway.)

The reason I had to identify the wires is that the colors didn't match what I see here: http://www.therangerstation.com/tech_library/TrailerLights.shtml

Anyway, I connected up the 4-prong flat connector as required above (and in the package the connector came in) and the trailer lights didn't work properly. Hard to describe, but dim instead of bright for signal and stop lights, only one when both were required, etc.

So back to square one, rechecked the connections and then I found the one I had previously identified as ground was no longer ground. Hooking up the trailer hitch, I got better results. Both taillights worked, but the right brake/signal light didn't. Looks like the ground through the hitch helped a bit, but taillight voltage was only 8.5v. (I checked that when checking the trailer lights in case that was the problem.)

Anyway, I have no ground at the end of the harness and no RH bright voltage. I'm suspecting a problem in the rear harness. Any pointers exactly where to look?

 

[Trey3495]

Your problem is poor ground. Just find a good ground on the truck frame and connect the ground wire from the harness truck side. Make sure the ground wire on the trailer is also well attached.

 

[Spott]

Also, unless you've seen it working, don't assume the trailer wiring is good.
Even if you've seen it working, it may not be wired correctly. Occasionally someone will mis-wire both their truck and trailer in a complimentary way, so that they work great when hooked together, but won't work right with any other truck or trailer.

 

[oldyellr]

@Trey, that's what I plan to do, connect the trailer harness ground wire directly to the frame. It still doesn't explain why the RH flasher/brake circuit is dead also. I could patch a feed for that from the truck's taillights, but since the truck has separate lights for the brakes and turn signals, I'd have to feed from both and use diodes. That makes me wonder if the truck trailer harness has diodes in it somewhere that have failed.

@ Spott, the trailer is quite new and the lights worked on 2 other vehicles.

 

[oldyellr]

The more I think about it, I believe the Ranger trailer wiring harness has to have a diode converter built in. Back in the day, converters weren't needed because vehicle taillights and trailer lights just had an 1157 bulb on each side. Then, when domestic cars started to copy imports with separate brake and signal lights, converters were needed because trailers didn't follow suit. Not wanting to remove and tear apart the harness to find the failed diodes and open ground, I guess my only option is to bypass the problem with a chassis ground and my own diodes.

 

[enjr44]

The last time I looked they still make a trailer connection kit for the truck that have separate turn and stop lamps. You pull apart the wiring harness connector under the bed and put the kit's "pass through" connector between them. The last time I saw one was at an Advance Auto. I think if I were looking for one, I would talk to someone at a big U-haul place. They have to do it all the time.

 

[oldyellr]

Etrailer has a kit

https://www.etrailer.com/Custom-Fit...Ranger/1998/118325.html?vehicleid=19981172317

However, shipping to Canada is pricey.

What I ended up doing is bolting the ground straight to the frame and running a wire from the right taillight brake and turn signal , isolating the two with diodes to prevent feedback. I actually put 3 1N4001 diodes in each leg for more current. Everything now works, except you don't see the RH trailer light flashing when the brakes are on. My electronics knowledge doesn't go much beyond diodes, so this will have to do for under $20 total.

 

[martin]

If you just want the five wire to four wire converter, Walmart has them for around ten bucks.

 

[oldyellr]

I don't see one that cheap here. However, my original intention was not to cut into the existing wiring harness, but use the 4-wire branch I found that had been cut off. Turns out that it was probably cut off for a reason. The ground and right turn/brake wires didn't work. That's why I had to wire those separately.