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)

JustinID View Member Profile	Jun 8 2008, 05:14 PM Post #2
Member Group: Advanced Members Posts: 126 Joined: 28-June 07 From: Idaho Member No.: 1,834	John - There are spots that the wiring has to go through the frame, but there's no other way around it. At least all of those points are painted and not too awfully sharp. It's a 4' by 4' utility trailer. One of those cheapo Harbor Freight ones. The good news, however, is that I found the problem. The guy I bought the trailer from added a bar in the back that would allow it to be tipped up on its back edge for storing it vertically. It looks like when he tightened one of the bolts, he caught a wire and smashed it. That broke the insulation open and the bolt was tied straight to the frame, allowing it to ground out. I got the wire unpinched, taped it up, and now the trailer is working fine. I've run into another unrelated problem that I think I've had with my car's brake lights for a long time, but I'll post that up in a new thread. Thanks for the help guys, I'm glad it was an easy fix. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/smile.gif)

TxAgZ28 View Member Profile	Jun 9 2008, 05:44 AM Post #3
Member Group: Advanced Members Posts: 248 Joined: 29-December 03 From: San Antonio, TX Member No.: 63	QUOTE (JustinID @ Jun 8 2008, 12:14 PM) It looks like when he tightened one of the bolts, he caught a wire and smashed it. That broke the insulation open and the bolt was tied straight to the frame, allowing it to ground out. I got the wire unpinched, taped it up, and now the trailer is working fine. It's always the smallest, dumbest things that cause us the most frustration (IMG:http://www.frrax.com/rrforum/style_emoticons/default/smile.gif) Glad to hear you got it sorted out!