Short? when hatch is closed....??

[kurtibm]

Hi All,
I'm an electrical rookie and am looking for some help on my completed trailer, please... (the trailer is about 8 yrs. old, this is a NEW problem (challenge))
When I have the headlights/parking lights on in my truck (attached to the trailer, of course) and have the hatch OPEN... all is well. (Turn signals - OK, brakes - OK, running lights - OK)

If I, however, close the hatch, I can hear the alternator come under load in the truck and all of the trailer lights dim. If left this way long enough the parking light fuse in the truck will blow. If I open the hatch, the alt unloads and it goes back to "fine".

With the trailer connected, and the hatch DOWN, but without the lights turned on, all seems to be well.

Any ideas???

Thanks in advance,

Kurt

[Denzagrad]

Hi All,
I'm an electrical rookie and am looking for some help on my completed trailer, please... (the trailer is about 8 yrs. old, this is a NEW problem (challenge))
When I have the headlights/parking lights on in my truck (attached to the trailer, of course) and have the hatch OPEN... all is well. (Turn signals - OK, brakes - OK, running lights - OK)

If I, however, close the hatch, I can hear the alternator come under load in the truck and all of the trailer lights dim. If left this way long enough the parking light fuse in the truck will blow. If I open the hatch, the alt unloads and it goes back to "fine".

With the trailer connected, and the hatch DOWN, but without the lights turned on, all seems to be well.

Any ideas???

Thanks in advance,

Kurt

Basic assumption: You have a license plate light attached to the hatch. Based on this assumption and your symptoms it sounds like a classic partial wiring short, most liklely in the small section of wire running from the hatch to the trailer. The symptoms match the trailer license plate light wires touching together when closed creating a short. The license plate light is usually on the same electrical circuit as the running lights.

[Woody]

Sounds like a short to me as well. I had one too, It turned out that I had run a srcew partially into a wire during the build. It was a pain in the ass to find but I did and no more problems

[kurtibm]

The "license light" presumption is right on.

Well, to attempt to isolate the problem I unplugged the wires where they make the "jump" from trailer to hatch. This, of course, disconnected the license light. With that done, I closed the hatch with the running lights on and encountered the same issue as stated above.
The tail/turm lights are in the fenders and remain unaffected.

Further ideas anyone??

Thanks, guys, for the help thus far...

[Denzagrad]

The "license light" presumption is right on.

Well, to attempt to isolate the problem I unplugged the wires where they make the "jump" from trailer to hatch. This, of course, disconnected the license light. With that done, I closed the hatch with the running lights on and encountered the same issue as stated above.
The tail/turm lights are in the fenders and remain unaffected.

Further ideas anyone??

Thanks, guys, for the help thus far...

Depends on where you disconnected the license plate light. A rule of diagnostics is to keep dividing the circuit by two. To identify the problem circuit you will need to first isolate the entire circuit. For example, to confirm if the problem is in the hatch license plate wiring, you need to find the power tap point where that circuit taps into the running light circuit and open that circuit. Once disconnected, test the hatch again. If there is no difference then its not in the hatch license plate light circuit. If however, the problem goes away - then you will need to dig into the license plate light circuit by selectively opening it at different points, start with the light itself, then the point where it goes into the body and keep up till you find the location. Based on past experience it is usually a portion of the wiring that moves when the hatch is moved.

[kurtibm]

Thanks!
I now know my daily project...