Sorry I don't think I was very clear in my original post let me try with a picture. Red arrows I have power at Green/Yellow wires - blue arrow I have no power at Green/Yellow wires. You can see were I have stripped them back and tested for power before they get to the 7 pin harness.

 

Good graphic!

And you have power to multiple pins in the plug at the right and it corresponds to you turn signals and brake operation?

It looks to me like that is the main harness to the rear. Did you check the leads ahead of the juncture on the left, that is, do you have power on the leads immediately after the plug as in "to the plug and through the plug" in the right in your graphic?

Steve

 

Your right RV... also there is some variation in the wiring diagram for a car trailer or a motor home. Most car trailers do not have a backup light option, but some horse trailers or RV do. I think verifying the pin designation is a good idea.

 

 

I run into the color issue so often, I totally ignore it when I wire.

I wish they would stop noting it on the Internet examples and simply note the relationship between pins and functions. I think it would stop screwing up a lot of folks who think colors are universally designated when it actuality they may mean nothing at all.

Steve

 

Maybe a better picture--------

 

You are right, it is better, but I wish they would leave out the colors completely. It is fine if you are used to wiring, but a lot of folks aren't and that is always my concern.

Some of the dump trailers I have wired are crazy. They actually spliced leads and changed colors for the same function three times on a single lead. The color you started out with had nothing to do with the color you ended with or the color you traced mid-way in the circuit.

 

I have also seen where they put the brake wire in the middle, or the 12 v wire in the middle, or switch the black and blue and brakes lockup when you plug in the harness.

 

That's the craziness. Once you understand this stuff you quickly realize you can wire it anyway you want as long was you understand what you are doing and match your trailer to your truck. Of course the next owner is screwed, but a lot of folks don't consider that!

 

Took the loom off the entire thing and got a closer look. There are separate wires that come through that harness for the truck turn/brake lights and the trailer turn/brake lights. I assumed it was the same wire and the trailer pin wires just connected to the main truck wires at that T. Wrong. So used the light tester on that plug again and yesterday when I got blinking lights at two of the pins I assumed my turn wires were good, but now I see the yellow/green that go to trailer pin are independent and those pins on the connector plug are testing no power. SO....I'm back to why those two wires have no power incoming. So went back and checked every fuse again, can't find any without power - but battery went dead while I was checking the last few and now I sit an wait while I charge it.
I need to figure out for sure which pins on that connector I don't have power too once the battery is charged back up. I know I had two that had power and I think they are black and orange, but I have to check it again.

 

I don't think this is a wiring issue. I think it is a power supply issue, which is what it sounds like you are gravitating towards also.

I don't know your specific truck, but I did a 99 250 not long ago and it had the box under the hood. I am guessing you checked that and you used your test light on both fuse legs so you know there is power to and through the fuses there.

Steve

 

Had to resort to a temporary fix as this truck must have trailer lights in the morning. I spliced the yellow/green to the green/orange on the truck to get power to the trailer turn lamps, everything now works. Still not sure why the trailer half of the wires are dead at the frame rail connector - this is tested at the incoming side of that connector so I'm certain it is a power issue not a wiring issue, at least not a wiring issue that's past that connector.

Orange - has power (Auxiliary)
Brown - has power (Running lamps)
Green - no power (right turn)
Yellow - no power (left turn)
Blue - no power (brake controller)
Black - no power (12 volt)

Tested every fuse both sides and everything else I can think of and I can't find the problem. Hopefully I can find the source of the problem and fix it correctly at some point. By the way the other half of the wires in that connector that power the rear lights/turn on the truck all have power and work as they should.

 

I think some have a trailer / tow relay fuse box under the dash to the right of steering column . I may be dreaming , but I think ..... I remember seeing that .

 

On a 98, the trailer turn signal/hazard lamp fuse (F#2) is in a fuse box up in the corner (driver's side) by the hood hinges.

Strangely, you have to look at the 1997 owner's manual to see it because the 1998 owner's manual doesn't have it in there.

 

Relays or fuses. Three wires down at the same time between box and first connection, an almost never thing.

Steve