- Jan 11, 2012
- 118
About a month ago, I was towing my utility trailer at night, and by the time we got home, I had no running lights on the trailer (but the brake lamps still worked on both sides). I checked the fuse box in the truck, and fuse #42 was blown (trailer parking lights).
The trailer has a 4 pin flat connector on it (converted to that by me).
An ohmmeter was revealing zero resistance from ground to any of the other three pins (brown, green, and yellow).
So I jacked up the trailer, and started inspecting wires. The left tail lamp (yellow) and left running light (brown) wires were both chafed through where they go through a hole drilled in the frame. Then I snipped that wire where it connects to the central harness (going down the middle of the trailer, and back at the brake lights, it is running along the wood floor via staples, so no place for it to ground out). I checked out all places where the wiring harness was running inside the metal channel for the tongue, and it is well insulated.
With that wire pair snipped, the ohmmeter was reading a more believable 4.7 kOhms between ground and brown, or ground and green, and infinite between ground and yellow.
Then I replaced the wire pair that I snipped, and put a rubber grommet in both sides of the hole through the frame where the brake/tail light wires pass to the left light. Now I'm back to ground to any other pin reading zero ohms. (assuming it is a short), A short inside the left hand light assembly shouldn't have any effect on the restistance from the right hand brake light wire to ground, but it does(!). The trailer only has two brake light assemblies (with the running light sub-function), no other lights (not even the required DOT amber forward markers-I was going to add those later).
Anyone have any idea what's going on here? I'm at whits end trying to think like a lazy electron...
Haven't tried hooking it up to the truck again yet.
The trailer has a 4 pin flat connector on it (converted to that by me).
An ohmmeter was revealing zero resistance from ground to any of the other three pins (brown, green, and yellow).
So I jacked up the trailer, and started inspecting wires. The left tail lamp (yellow) and left running light (brown) wires were both chafed through where they go through a hole drilled in the frame. Then I snipped that wire where it connects to the central harness (going down the middle of the trailer, and back at the brake lights, it is running along the wood floor via staples, so no place for it to ground out). I checked out all places where the wiring harness was running inside the metal channel for the tongue, and it is well insulated.
With that wire pair snipped, the ohmmeter was reading a more believable 4.7 kOhms between ground and brown, or ground and green, and infinite between ground and yellow.
Then I replaced the wire pair that I snipped, and put a rubber grommet in both sides of the hole through the frame where the brake/tail light wires pass to the left light. Now I'm back to ground to any other pin reading zero ohms. (assuming it is a short), A short inside the left hand light assembly shouldn't have any effect on the restistance from the right hand brake light wire to ground, but it does(!). The trailer only has two brake light assemblies (with the running light sub-function), no other lights (not even the required DOT amber forward markers-I was going to add those later).
Anyone have any idea what's going on here? I'm at whits end trying to think like a lazy electron...
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