Trailer wiring problem - F-Body Road Racing and Autocross Forums

I just wired up a 4 wire harness for my little tire trailer. It's behaving kinda funny and sometimes blowing fuses. The left light is somewhat intermittent in working Sometimes it won't turn on when braking and I think it didn't turn on the turn signal once. But other times it's just fine. Also, it's not just the trailer light, it's the car's left tail light as well. If one works, they both work. If one doesn't work, neither work. The right side brakes and turn signal work just fine. I'm getting ready to just say screw it to that and deal with it being funky.

The other problem I'm seeing is that I'm blowing the 20amp tail light fuse every time I turn on the running light or head lights. I don't understand why the brake lights can work, but only the running lights would blow a fuse. They both have 20 amp fuses and I would think that the brake lights would actually draw more power.

I hooked up a multimeter to a ground and to the light side of the tail light fuse holder (with no fuse installed) and learned that despite having a degree in computer engineering, I still can't figure out crap about analog circuits. With nothing turned on but the parking lights, and the tail light electrical plug (at the back of the car) unplugged, I'm seeing 0.7 ohms. That implies a 17 amp draw with the tail lights completely unplugged. Now if I turn on the headlights, the resistance drops to 21.4 ohms. Why would turning on the headlights effect the draw across the tail light circuit? Especially when the tail lights are unplugged??? If I turn the ignition on, then the that effects the readings as well. Plugging the lights in makes the resistance drop (potential load goes up) which makes sense, but why wouldn't there be no load if the lights are unplugged? This stupid car makes no sense to me. Or is it, this car makes no sense to stupid me. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/banghead.gif)

FWIW, despite the ohm readings that I can't make heads or tails of, the car does NOT blow fuses when the trailer is not attached.

In the end, I'm left wondering if the trailer is just drawing too much current and that 20 amp fuse can't keep up. I know it's normally a no-no... but what about just trying a larger fuse? 25 or 30 amp? If I can't get this going, I have no clue how I'm going to get power out to my trailer.

Someone please save me before I rip out what's left of my hair. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/tongue.gif)

JustinID View Member Profile	Jun 7 2008, 11:27 PM Post #1
Member Group: Advanced Members Posts: 126 Joined: 28-June 07 From: Idaho Member No.: 1,834	I just wired up a 4 wire harness for my little tire trailer. It's behaving kinda funny and sometimes blowing fuses. The left light is somewhat intermittent in working Sometimes it won't turn on when braking and I think it didn't turn on the turn signal once. But other times it's just fine. Also, it's not just the trailer light, it's the car's left tail light as well. If one works, they both work. If one doesn't work, neither work. The right side brakes and turn signal work just fine. I'm getting ready to just say screw it to that and deal with it being funky. The other problem I'm seeing is that I'm blowing the 20amp tail light fuse every time I turn on the running light or head lights. I don't understand why the brake lights can work, but only the running lights would blow a fuse. They both have 20 amp fuses and I would think that the brake lights would actually draw more power. I hooked up a multimeter to a ground and to the light side of the tail light fuse holder (with no fuse installed) and learned that despite having a degree in computer engineering, I still can't figure out crap about analog circuits. With nothing turned on but the parking lights, and the tail light electrical plug (at the back of the car) unplugged, I'm seeing 0.7 ohms. That implies a 17 amp draw with the tail lights completely unplugged. Now if I turn on the headlights, the resistance drops to 21.4 ohms. Why would turning on the headlights effect the draw across the tail light circuit? Especially when the tail lights are unplugged??? If I turn the ignition on, then the that effects the readings as well. Plugging the lights in makes the resistance drop (potential load goes up) which makes sense, but why wouldn't there be no load if the lights are unplugged? This stupid car makes no sense to me. Or is it, this car makes no sense to stupid me. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/banghead.gif) FWIW, despite the ohm readings that I can't make heads or tails of, the car does NOT blow fuses when the trailer is not attached. In the end, I'm left wondering if the trailer is just drawing too much current and that 20 amp fuse can't keep up. I know it's normally a no-no... but what about just trying a larger fuse? 25 or 30 amp? If I can't get this going, I have no clue how I'm going to get power out to my trailer. Someone please save me before I rip out what's left of my hair. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/tongue.gif)

trackbird View Member Profile	Jun 8 2008, 02:05 PM Post #2
FRRAX Owner/Admin Group: Admin Posts: 15,432 Joined: 13-February 04 From: Ohio Member No.: 196	Also, are you using a trailer converter box for your lights? You should have amber turn signals on your car so you should use the "box of diodes" isolator to isolate the turn signals from the tail lights.

JustinID View Member Profile	Jun 8 2008, 03:45 PM Post #3
Member Group: Advanced Members Posts: 126 Joined: 28-June 07 From: Idaho Member No.: 1,834	QUOTE (trackbird @ Jun 8 2008, 08:05 AM) Also, are you using a trailer converter box for your lights? You should have amber turn signals on your car so you should use the "box of diodes" isolator to isolate the turn signals from the tail lights. Kevin - based on the a similar conversation you had here, I learned that the 5 to 4 wire box I have wasn't what I needed. I did try to find a straight 4 wire harness with diodes, but was unable to do so. The guy at the autopart store where I got my 4 wire harness said that the only possible downside to not having diodes was that my blinkers would flash rapidly if I didn't have a "heavy duty" blinker unit. Aparently when I replaced my blinker module a few years ago, I got a heavy duty one because it does blink normally when it's all plugged in. John - I'm about to start pulling the wires off the trailer so I can more closely inspect them. If that doesn't pan out, I figured my next step would be to start cutting the wire to narrow down where the short is. Is there an easier way than all that cutting and resplicing to find it? My last ditch effort will be to rewire the whole thing, which I'd rather not have to do. Thanks to everyone for the help and input.