I'll be running new wire for tail lights on a '78 that had some real jerry rigged wiring. It's a mess. For the most part I know which wires to run where but there are a couple that have me guessing.

Black/Red=Back Ups
Green=Right Rear Signal
Yellow/Black=Left Right Signal
Brown=Power
Black=Ground
Light Blue=??
Brown/White=??

My question is why are the Light Blue (is this for blinkers and splice into the yellow/black) and Brown/White wires back there? Are they for other applications under the truck? The gas tank is wired and taken care of already. Any help is appreciated thank you!

 

Here is some copy and pasted info for you.

Factory wiring diagram says for rear lights.
Blk/rd= backup lights
Black= side marker, tag lights (on styleside)
Brown=tail lights, tag light (on flareside)
green= RH stop and brake
Yellow/blk= LH stop and brake

Rear light wiring
BROWN: running light circuit
YELLOW with BLACK stripe: driver-side stop/turn
GREEN: passenger-side stop/turn
BLACK with RED stripe: backup lamps

73 & 79 headlight-marker lights use same color codes
Brown= side marker and parking lights
White-blue trace= turn signal
Red-black trace= Low beams
Green-black trace= Hi beams
Black=ground

Flat bed wiring…
Brown= Run Light
Green= Brake light- L
Yellow= Brake Light- R
Black= Reverse Light?

The brown wire is the marker light (side and turn) it is also the top wire on the turn signal socket (three wires in a triangle). The black is ground of course. The white/blue it the turn signal.

 

77&79F20, this is great info. I've actually read it a number of times in the past few days and it has helped! I've also studied the schematics.
But I don't see any information on the Light Blue wire or the Brown/White wire that are on this truck. I don't see them listed in the schematics. Maybe I'm missing something when reading through everything but that is where I'm confused.

Correct me if I'm wrong but looking at the schematics....I see a Light Blue/Black wire splicing into the Left Rear Turn Signal. Maybe this is the Light Blue wire on the truck I'm wiring? (I don't see a Black tracer on it though)

As for the Brown wire, that should be power. The Brown wire and the Brown/White wire both run to the wiring harness of the truck beside each other. So why isn't there a Brown/White wire on the schematics and where would the Brown/White be needed in the rear of the truck if the Brown power wire is already there?

Again I really appreciate the help. I'm trying to understand this mess. If anything else, I may have to crawl under another truck one of these nights.

 

I wasn't present when the wiring was ripped apart from the bed. Even though it was a spliced mess, I would have traced it all and labeled everything when taking it apart and probably wouldn't have these questions.

 

Did some more research may have answered my question....follow the link to this schematic:
http://fordification.net/tech/images...aster_6of9.jpg

If you look at the right center of the drawing, at connection "C-1105", this could be where the Brown and Brown/White wires connect. Next, go to the next connection "C-1001" and you'll see a Blue wire connecting to a Brown with the Note: "With Trailer Tow Only"

So if I'm interpreting this right, which I may not be, the Brown/White & Light Blue wire are for a trailer connection. Does this sound correct?

 

Blue wire is usually the power to the elec trailer brakes, if the trailer has elec brakes. Did you look at these?

 

Okay thank you I think that answers my questions then.

I did use those first 2 drawings, it's very hard for me to see the second two. I appreciate the help in answering the questions I had. I'll continue wiring tonight. The two wires I was concerned about are obsolete.

 

Hope it helped. As far as pic on the FTE, copy (save pic as) and past to you computer or lap top as a pic/jpeg in your pic or doc folder. Then you can zoom and hopefully they do not get pixelated.