Problem with Trailer Wiring (or Not)?

[colnago]

Gents,

Okay, so I am planning a road trip tomorrow, and need to set up the wiring for a trailer. I picked up a 4-pin harness today. It has the LEDs at the plug, so you can check your wiring out before picking up the trailer. I printed out the '67 wiring diagram on the Tech pages ( again), and found that the wire colors on the trailer dongle match the wire colors of the truck. Cool! I am cookin' with oil!

The install was absolutely painless. Turned on the left signal, and the left LED blinked. Right signal, right LED blinked. Headlights, and the tail light LED came on. This is the easiest trailer wiring harness I have ever put in! Whoever put in the test LEDs was a genius!

Next, I turned on the headlights and the left blinker. Nothing. Right blinker, same thing. WTF?!? Brakes, and the left and right LEDs held steady; turned on the blinkers, and they went dead. AAAUUUGGHHHHHH!!!!!

Now what? Did I do something wrong, or does the truck draw enough current that the LEDs don't work when you have two things happening? I KNOW that I didn't get the wires hooked up to the wrong leads, and even if I did, they are completely isolated from each other within the trailer harness.

Thanks,

Joseph

On edit, I just tried it with the engine running, and added another ground wire (just in case the ground point was suspect). Same results: one "function" works, two don't. Hmmm ....

[71PA_Highboy]

Sounds like a bad ground.

[colnago]

Well, I guess this is a false alarm. I just picked up the trailer, and its lights worked like they should. The LEDs on the trailer hitch still aren't blinking, but their sole purpose was to help me hook e'm up correctly anyways. I did try grounding the white wire to several places on the chassis, and even took an ohmmeter to the white wire and the chassis. Wherever I checked, it came back good. So, I dunno.

The one disturbing finding was that my truck is a Camper Special, so it has a trailer wiring harness coming back along the frame. I didn't use it originally because it has been hacked to pieces in the past 45 years. But I decided that its white wire might provide a better ground. Since I was just testing it, I put a straight pin through the wire, then checked it against the chassis: 0 ohms. Next, I used a jumper wire to connect it to my new harness ground. When I turned on the tail lights and one of the signals, I didn't have any new behavior (nor did I really expect any, because this was just another ground). So, I decided to remove the straight pin from the old harness ... and found that it had melted in half!

Looks like I'll be spending some time chasing down electrical demons! The silver lining in all of this is that a straight pin makes a pretty cheap, low-amperage test fuse!

Joseph