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trailer wiring help

cochino12

cochino12

1/2 ton status
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Dec 23, 2003
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Parker, Co
Can anyone tell me how to wire this dang trailer harness? I have a flat 4 pin harness and dont know what goes where, all I know is that white is ground. There is also a green, yellow, and a brown wire. I dont have anyone to hit the brake here and test the brake wire so I was hoping someone here might know what colors go where. thanks for any help
 
Have you checked at local auto parts stores? I know for the later weather pack style tail light harnesses, you can easily find the reese(?) "plug and play" wiring harnesses for trailering.

Cutting/splicing your wiring is a horrible idea. From what I've seen, trailer wiring is the #1 cause of tail light issues on the trucks. Besides that, to me, trailer wiring is somewhat of a pain for how simple it is...are the lights grounded to the trailer through the ball, or through the wiring harness itself? Which wire is turn signal? Etc., etc. as you are finding.

If you don't have ANY other choice, then cut/splice. That should be your absolute last option though. The plug and play harnesses I've seen are around $15 new.
 
What I did was buy the plug in harness from Wal Mart , Autozone , Napa , etc. I undid the original owners splices , and retaped the wires so it was basically stock again . Then I took the new plug in harness , undid the passenger side tailight harness plug , plugged in trailer harness , and replugged the passenger tailight harness in . Thats the best way to do it , plug and play :)

But , if you no one answers , I can go home tonight and pull up a wiring diagram to show what the factory colors were , and you can see what colors you have hooked to those . Will be later tonight , I have 4x4 nite at the bar first :D
 
wiring dilema's...

I strongly reccomend the "plug and play" harness too--for less than 15 bucks its well worth it,especially if your harness hasn't been butchered already--best part is it will take 10 minites to install rather than an hour or 2 of poking wires and your fingers with a test light...but if you must hack the harness,here's what wire does what....

BROWN== parking/running lights
LIGHT GREEN=back up lights
YELLOW==brake/directional lights

Its been quite a while since I did any wiring on my tailights,if I remember right you have to couple the yellow wires together so both sides work,and I dont remember how you get the right and left directional not to blink at the same time-:confused: --if I were you I'd buy the "T" that plugs into your original harness and be done with it--who wants to screw around with wires all day,only to have them corrode and give you greif later..:crazy:
 
BROWN== parking/running lights
LIGHT GREEN=back up lights
YELLOW==brake/directional lights
Click to expand...

Yellow is for the Left turn/brake light
Dark Green is for the Right turn/brake light
 
And not that it matters much... but I have 4 pin connectors on my trailers and have had to more than once replace the connectors because the pins pull out of the rubber things. I plan to switch to a 6 pin round connector to fix this problem. I will use the extra 2 pins to wire up some "back up" lights on the trailer to help me back it up at night and make it easier to load stuff.
 
divorced said:
I will use the extra 2 pins to wire up some "back up" lights on the trailer to help me back it up at night and make it easier to load stuff.
Click to expand...

Not a bad idea!
 
Ya, I was planning on putting 2 of them at the end of the trailer, and maybe a couple at the front also to make it easier to hook up tie downs underneath trucks.
 
Memory loss

Yup,its been a long time since I had to fix my tailights!--I was using my haynes manual's wiring diagram to refresh my memory,and they didnt list the light and dark green wires ,their diagram shows both tailights using the light green wire,which of course is WRONG!--I KNEW there was more wires!!:( --durn books are wrong a lot when it comes to wiring diagrams(and you go blind trying to read them--can they print it any smaller?:mad: :blush: )

A friend of mine uses a houshold 110V outlet box(the weatherproof outdoor kind with the spring loaded covers on the outlets) as a trailer plug ,and uses the cheap 3 wire extension cords for the trailer light harness--he doesnt bother with a ground unless it gives him problems,usually the ball itself grounds it good enough as it is--and its no big deal to add 1 more wire with an alligator clip for ground---on later trucks with computers a trailer plug can cause ECM damage if its not grounded good though--I think they make an "isolator" now to keep voltage surges out of the trucks harness to prevent damage to the computer...
 
dyeager535 said:
Have you checked at local auto parts stores? I know for the later weather pack style tail light harnesses, you can easily find the reese(?) "plug and play" wiring harnesses for trailering.

Cutting/splicing your wiring is a horrible idea. From what I've seen, trailer wiring is the #1 cause of tail light issues on the trucks. Besides that, to me, trailer wiring is somewhat of a pain for how simple it is...are the lights grounded to the trailer through the ball, or through the wiring harness itself? Which wire is turn signal? Etc., etc. as you are finding.

If you don't have ANY other choice, then cut/splice. That should be your absolute last option though. The plug and play harnesses I've seen are around $15 new.
Click to expand...

Cutting and splicing a wire harness can be reliable if done correctly, but I would leave it as a last resort.

To properly splice into a harness first don't even think of getting those little plastic splice connectors. They will work for maybe a year before they corrode. What you want to do is get yourself a butane pencil torch and a roll of flux core solder. Also pick up some heat shrink tubing. Put the shrink tubing on the wire then solder your connection. Then you slide the tubing over the solder joint and when you heat it with the torch it shrinks over the joint making a weathertight seal. I have rewired 3 trucks this way due to shoddy jackass style splices.

electrical tape is not weatherproof people.
 
gravdigr said:
Cutting and splicing a wire harness can be reliable if done correctly, but I would leave it as a last resort.
Click to expand...

Show of hands of trucks that PO's have correctly wired on this board? :)

A 3 wire splice is pretty much impossible to seal from corrosion, which is why the plug in trailer harnesses are so good. Even the factory tapes up 3 wire junctions....GM just tries to avoid them.
 
I didnt think the plug in harness was available for a vehicle as old as mine, thats the last time I listen to those idiots at checker auto parts (I am an idiot for believing him too).

I went to napa found a plug in harness and they still dont work right though, I have no brake lights, left turn signal activates left turn signal on trailer but the park lights work ha ha. Looks like I am going to have to hardwire it anyway :mad:

Of course the PO hacked into these wires too, WTF do are people thinking when they half A$$ things. Dont they realize it makes things more of a pain in the butt?
 
If your truck lights work ok, but the trailer ones don't even after you put in the "harness", then the problem exists with the trailer wiring, not the harness or your truck taillight harness.
 
cochino12 said:
I didnt think the plug in harness was available for a vehicle as old as mine, thats the last time I listen to those idiots at checker auto parts (I am an idiot for believing him too).

I went to napa found a plug in harness and they still dont work right though, I have no brake lights, left turn signal activates left turn signal on trailer but the park lights work ha ha. Looks like I am going to have to hardwire it anyway :mad:

Of course the PO hacked into these wires too, WTF do are people thinking when they half A$$ things. Dont they realize it makes things more of a pain in the butt?
Click to expand...

Take it off and on a couple of times , I forgot to mention that at first it won't make a good connection , just unplug a couple of times and make sure its pushed together tight and your lights will come back ......seriously :D
 
pauly383k10 said:
Take it off and on a couple of times , I forgot to mention that at first it won't make a good connection , just unplug a couple of times and make sure its pushed together tight and your lights will come back ......seriously :D
Click to expand...

ha ha I'll try that tonight.

I think the trailer is wired correctly, maybe I'll try and plug it into my other truck and see if the problem is still there.
 
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