Tail light wiring harness color meaning

[AuroraGirl]

The tail light harness that comes from the front of the truck meets the rear harness at a connector. The harness has 4 wires. Dark Green, Light Green, Brown(possibly black), and Yellow. Does anyone know what wire does what function (tail, stop, left, right)?

I want to wire in trailer light socket off the truck and Its cold to probe the harness on the ground with a helper or brick. I mean, I can do it but if someone just already knows that would be helpful. I tried my 1980 service manual but I could not find the color meanings unless Im just not looking in the right spot.

 

[DBarre]

It's the same as trailer wiring, but with the light green added for reverse.

dark green: right turn
brown: tail
yellow: left turn
light green: reverse

You will need to add a ground.

They actually make an adapter plug that tees off and gives you the 4 pin trailer wiring out of it. https://www.etrailer.com/Custom-Fit-Vehicle-Wiring/Tekonsha/118311.html There are different versions so make sure it fits the plug you have.

 

[AuroraGirl]

Haha thanks. And actually, I only am doing this BECAUSE the original plug is gone. So I was going to use a universal 4 wire plug and hook it up so I can save some money. I want to get the harness that has a 7 prong premade into it, which that harness guy sells, but Im holding off till the truck is seeing road use. For now, just so it works. Even if I dont use a trailer I like to have the option if i were not to get to it right away.

And thats happy to hear about the wiring, I guess I assumed light green because it matched trailer but it makes sense given that the bright green goes off two ways, hence reverse.

However, does that mean reverse does not run this wire loom, then? Does it go straight to the switch on the... trans? Which if it is, I will need to find out where that switch comes off the manual transmission

And the ground wire is good, I had no issue finding it and knowing it was a ground on my replacement wire harness. I guess another question on ground is does it have a specific spot it grounds or does it just ground on the frame? I know at the other end it grounds on the driver side bed at the light fixture.. whch now that I typed that makes me wonder where the ground cable does go.

 

[75gmck25]

The stock ground wire is a larger diameter white wire, grounded to the frame up behind the back bumper. It doesn't matter exactly where its grounded, but you should carefully clean the frame and use a star washer for a good connection.

I'm confused about your "reverse" wire question? The backup lights wire is there in the loom (light green), but a stock 4 wire trailer plug does not have a backup lights connection. You would need a 7 wire plug and a trailer wiring loom that supports it.

Bruce

 

[Matt69olds]

The neutral safety switch also contains the switch for the reverse light. If I remember correctly the switch is fused on the turn signal fuse by a dark green wire. It comes out of the switch on a light green wire.

 

[AuroraGirl]

The stock ground wire is a larger diameter white wire, grounded to the frame up behind the back bumper. It doesn't matter exactly where its grounded, but you should carefully clean the frame and use a star washer for a good connection.

I'm confused about your "reverse" wire question? The backup lights wire is there in the loom (light green), but a stock 4 wire trailer plug does not have a backup lights connection. You would need a 7 wire plug and a trailer wiring loom that supports it.

Bruce

Im asking where the light green connects if not to the wire harness. I know its not apart of the 4 wire connector for trailer wiring, just curious where it goes since on my harness its the same length as the other ones and is hanging out with them. On a manual, does it just go along the frame to the trans, perhaps? clutch safety perhaps?

 

[DBarre]

Im asking where the light green connects if not to the wire harness. I know its not apart of the 4 wire connector for trailer wiring, just curious where it goes since on my harness its the same length as the other ones and is hanging out with them. On a manual, does it just go along the frame to the trans, perhaps? clutch safety perhaps?

All 4 wires you described (dark green, yellow, brown, light green) go from the rear of the truck along the frame to the fuse block in the cab. From there, who knows? But that doesn't matter as long as it works.

The rear harness should plug in (to the plug you say is gone) and split off to each taillight as well as the license plate light. Each taillight has tail, turn(brake), and reverse. License plate light has only tail. Somewhere in the harness there is a shared ground for all the rear lights.

The stock ground wire is a larger diameter white wire, grounded to the frame up behind the back bumper. It doesn't matter exactly where its grounded, but you should carefully clean the frame and use a star washer for a good connection.

I hope that helps.

 

[AuroraGirl]

I cared about where It goes because I assumed it didnt follow the harness, but I see what it is now. The shared ground, I was assuming that wire went further up the line, but I get it now.

 

[AuroraGirl]

This is what Ive done. I mated the matching trailer wiring to the correct colors on the taillight harness, with the white ground and black ground wire unconnected, as I will ground those to the frame. The harness on truck and this one both have a black wire for this ground, so Im not sure what years had white but its okay. I figure Ill use a O hook end and some self-tapping screws with the lock washer the previous guy mentioned.

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[Kevin McDermand]

This is what Ive done. I mated the matching trailer wiring to the correct colors on the taillight harness, with the white ground and black ground wire unconnected, as I will ground those to the frame. The harness on truck and this one both have a black wire for this ground, so Im not sure what years had white but its okay. I figure Ill use a O hook end and some self-tapping screws with the lock washer the previous guy mentioned.

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Hello, are you sure the black wire from the truck wiring was a ground? I just finished wiring my truck with a brake controller and a 7 pin connector and I don't remember a black wire that was a ground. I'm not an expert but could it be an auxiliary power wire to the trailer?

 

[AuroraGirl]

I think I know what it is. Thank you for bringing that up.

Hello, are you sure the black wire from the truck wiring was a ground? I just finished wiring my truck with a brake controller and a 7 pin connector and I don't remember a black wire that was a ground. I'm not an expert but could it be an auxiliary power wire to the trailer?

I think its the tail light for the other side... I just didnt clean the wire any further. Can someone confirm the wire for tail light goes up the harness to the connector(which mine was originally cut off)?

Both sides have brown wires that go to their respective sides, that of course goes to the side marker AND main bulb, which tells me tail light, which makes me 90% sure this is the case. Thank you so much for bringing that up so I can resolder properly before bringing it to the truck and putting it on.

 

[AuroraGirl]

Infact, I can see the part of the wire where it was tapped into by the wire taps for trailer wiring.

 

[75gmck25]

GM uses both black and white wires for ground. It seems that the engine compartment and instrument panel use black, while courtesy lights, tail-lights and turn signals use white.

Bruce

 

[gmachinz]

On my 7-round Pollak trailer kits, black is +12V and white is chassis ground. All other tail lights wires share a ground that is attached to the bed body behind the tail light lense housings.