Magic lights!

[ericjan2]

All, Tonight I went out to the shop where I'm restoring my 77 31' International Sovereign. I am plugged into 110 power for the coach but don' have the rig plugged into my tow vehicle. The rear tail lights are on and I can't figure out why? Can someone point me in the right direction. I'm sure if my rear tail lights are on all night in a campground it may upset my neighbors! Thanks......Eric

[Wazbro]

Someone in the site next to me at the campground I was at a couple weeks ago had a plastic cap on the 7-pin cable that filled up with water and made a connection which made the tail lights come on. I suggest looking for something similar.

[richard5933]

The symptoms do suggest that you've got a short between the tail lights circuit and another 12v+ circuit, and corrosion in the 7-wire harness could do this.

[ericjan2]

I'll have my wife watch the lights as I jiggle the wires going into the distro board. If they flicker I've found a good place to start. The pig tail 7 pin is original so it couldn't hurt to replace it also......

[NevadaGeo]

If that don't work, look for something laying on the fuse board like a jumper wire across the glass fuses.

[azflycaster]

Since the power for tail lights as well as running lights and brakes comes from the tow vehicle and not the trailer, the 7 pin connector is a good place to look. On many 70s trailers the 7 pin cable could be unplugged at the trailer. If yours is like that, unplug the cable and try it.

[ericjan2]

Well, I unhooked all 7 wires from the plug, then hooked them up one by one, and plugged in the 120 power on each of the 7 pins. The ones that are lighting up the tail lights are the green and the yellow, either or! The green by itself lights the the tail lights and the yellow by itself turns on the tail lights! When both are hooked at once it lights the tail lights! Should I procure a new 7 pin connector or do you think there's a correlation between the green and the yellow somewhere along the line between the lights in the rear and the 7 pin connector in the front? The battery isn't hooked up in any of these scenarios. Only the shore power. Hummmm!

[richard5933]

Something isn't right with the testing...

The power going to the 7-wire plug/harness is 12v DC only. There should be absolutely no 120v AC on the 7-wire hardness.

Coming from the tow vehicle, there should be the following in the 7-wire harness:

- 12v positive

- 12v negative

- Electric brakes

- Left turn/left brake light

- Right turn/right brake light

- Tail lights & marker lights

- Reverse lights (not on all trailers)

The color of the wires will vary from year to year and even trailer to trailer. The position of the wires in the plugs is pretty much standard, and the exact layout should be in your manual.

To test the lights on the trailer, you need a 12v DC power source, like a 12v battery. Connect the negative of the battery to the pin which is shown as 12v negative in your manual's diagram, and then connect the 12v positive to the lighting circuits one at a time to see what lights up.

If you're getting things crossing over from one to another, my guess is that either a) your 7-wire harness cable was crushed or cut at some point in time and is shorting, or b) the junction point where the trailer's wiring connects to the 7-wire harness has been compromised.

If both of these areas are okay, then you've got a short elsewhere if the lights are cross firing.

[azflycaster]

I believe if you had a battery installed, you would have tail lights all the time. When you plug in to shore power, the 12 volts is coming out of the converter. Green is tail lights and yellow is backup, but wire colors and pin positions have changed over the years. The black wire is the 12 volt power and I would expect the tail lights to not turn on if that wire is disconnected. If that is the case, somewhere in the wire/connector the 12 volts is shorting to the other wires.