Trailer lighting question... just the lights. (2001 Silverado)
 

I've been doing my homework on this for almost a damn month now and I never would have guessed these 4 stupid wires can be such a pain in the ass..

Anyway.. I've dealt with this at work a couple times, but mostly fixing clipped cables and repairing the connectors.. But never installing from scratch.

I took a job to fix a buddy's hacked up wiring because he was taking it out of state that evening. I gave him a temp fix to get him by but I'm not happy leaving it like that so I'm going to make it permanent and I have to do my truck now too.

I asked my uncle who was a GM master tech for quite a while and he told me how to do the OEM way of connecting the leads under the fuse block, install the appropriate fuses and then go in the cab by your left foot and connect the harness there, that goes to the trailer lighting.


So I popped the cap off the junction block and I'm sorry but I can't make heads or tails out of this and It doesn't even match anything. ???? :huh: Normally I'm decently good with wiring (been around that block many times) but this is just giving me a headache. It looks like a relay block diagram but it doesn't match this block.... at all.. :huh:

Does anyone have a pic of this block where the LIGHTING connector would plug into and something that I can make out where each lead has to go for L,R, Brake and Marker. I have a converter box that's on his truck now. he has an 01 1500 Silvy and I have a 2000 2500 Silvy.


Here's my block and the cover. I'm sorry if this sounds stupid, but I'm losing my mind here..

https://scontent-lga.xx.fbcdn.net/hp...64&oe=555E3E2A

https://scontent-lga.xx.fbcdn.net/hp...70&oe=555DDEB0

I was basically wanting something like this to Tie into the junction block in the back. And just add bigger fuses up front.

https://guideimg.alibaba.com/images/...lack_39959.jpg

gmupfitter.com has a lot of these types of diagrams I believe. That box down by your left foot is called the MBEC (mid bussed electrical center), might try to search for MBEC wiring pinouts or diagrams too.

See attached image this is from my 2000 silverado. This is were the brake controller plug attaches. The one that is not wrapped in tape is coming from the brake controller.

Edit: Stupid mobile turned it sideways, I corrected it putting it upright and put an arrow pointing to the harness plug for the Brake controller.

The Wiring from the rear 7 port round plug Pigtail goes to the under hood fuse box. Lug goes on top of a battery post there, and the other wire will attach to the blue plug that is not connected to anything.

Picture of blue plug stolen from here... https://www.performancetrucks.net/fo...-power-537466/

I also attached the GM conversion harness directions so you will get a better understanding of what's involved. That harness your looking at should have some instruction as well.

I don't need the brakes, but thanks still! Very helpful!

My 2000 Truck has the older 5 pin round lighting connector and the wiring (finally checked today) so I have to start from scratch on my buddy's truck...

After re-reading your post, I'm not sure that I understand what you're after. I don't recall there being anything other than a plug for the trailer brake controller under the dash...IIRC everything for trailer lights would be in the underhood fuse block only. There wouldn't be any reason for the light harness to route through the cab.

Am I understanding correctly that you're trying to add or activate circuits in the underhood fuse block for trailer left, right, and running lights, and that's it?

I think whoever explained the lights to you overcomplicated things. You need three power leads, one for left turn, one for right turn, and one for parking lights. The 4th wire goes to ground. There shouldn't be any reason to go to inside the cab at all. The OEM trailer wiring also does not pass through the rear junction block.

You should just be able to install these three fuses and run wires to the back of the truck...


Attachment 92125

I think whenever I mention "trailer" and "wiring" in the same topic people automatically jump to the "brake controller" default which requires that 30a Maxi-Fuse, connecting leads and using that MBEC. This is why a google search was getting so frustrating after three weeks.

Whoever had my buddy's truck before him hacked into the wiring at the tail lights. and it was just bare wire twisted together with a little bit of electrical tape over it. So I just got rid of that and used butt connectors for now... it was JUST for TEMP! Not intended to be permanent. So they ran power to the trailer from that but there was no ground.... ??

I think the only reason the lights were working in the first place was that they were grounding through the trailer ball into the truck. I added a new ground right to the frame. He had a slew of blown fuses and blown bulbs. so I fixed all that, added the converter and added 5 Amps to the OEM fuse recommendation to compensate for the added lighting. It lasted for a couple hours till later that day when he said he lost everything.. ??? WTF now?! ok.. Whatever. I'll deal with it later.. Everything worked when I left it. I even put a big block of wood on the brake pedal (working alone) to test the marker lights and brake lights and signal lights and the brakes.

So now I'm going to solder the OEM harness back to stock and start from scratch and get rid of the hack-temp job.

So, short story long.. he's just asking for the lights and I guess my truck already has that so I have a little bit to draw from. I was looking to duplicate the OEM setup. It has an adequate power supply from the fuse block under the hood and I can re-pin a connector to work with the MBEC to run a basic 4 wire lighting harness to the back and use the converter if need be.

I'm basically going to be using your idea though. It's just taking me an abnormally long time to wrap my head around this project. Like they say, though, it's the simple shit that can throw you off.

Gotcha....I still dont think the OEM trailer lights run to the MBEC at all though.

I don't believe they do.

It should all be under hood fuse box as the wiring diagram suggest.

I am pretty sure, Only the brake control goes through there for the trailer brake function.

^ My light bulb just turned on...... After three weeks.. lol

got it... finished it friday but forgot to post. The stock system was in place and the harnbess was just capped off and tucked in above the spare tire.. Got everything hooked up and installed the converter box with it. No trailer brakes, so no MBEC involvement.

Soldered the tail light harness that was hacked up from the previous owner and from my temp fix. All is well. Just have to get a bracket for the plug.


This is what the PO had. with one fold of electrical tape over it. This is as bad as it gets.
https://scontent-lga1-1.xx.fbcdn.net...fb&oe=5566504A

Look how bad this was. The pass side was just as bad.
https://scontent-lga1-1.xx.fbcdn.net...a5&oe=5565C611


Fixed.
https://scontent-lga1-1.xx.fbcdn.net...e4&oe=556509AB

Yeah the reverse light is blown..
https://scontent-lga1-1.xx.fbcdn.net...07&oe=55664856

Heat shrink butt connectors for the trailer connector.
https://scontent-lga1-1.xx.fbcdn.net...35&oe=55661DCB

Wow, that's painful to look at. Good job getting it all fixed.

Wow, that was rough... I hate when people do stuff like that.

Is that corrosion where the wires are going into the tail light socket?

Yeah, it may be some corrosion. Everything worked again when I left, but I didn't have the trailer to plug into this time so I only checked the obvious stuff.

This truck is busting my balls... seriously.... He's still popping fuses... BUT only when the trailer is connected, so I'm thinking something is shorted in the trailer. Probably why half the marker lights along the top don't work. I tried replacing bulbs and it didn't work and the trailer was full at the time so I didn't really have access, and I was trying to clear up the hack work first. It's a good size enclosed trailer I've only worked with once. the back lights worked when I left the first time and that's all that really mattered for what he was doing. It's a good size trailer. I'm going to start checking the trailer this time because I'm using a factory harness on this truck now, so there's no reason it should be blowing fuses.




And on a side note... Got a ride in a buddy's 550 HP LBZ Dmax 3500 today. Purpose built for sled pulling.. :D Sounds so amazing!

Hook the trailer up to another truck and see if you can duplicate the fuses blowing. Also, try to hook a different trailer up to your buddy's truck. Follow the problem from there...

^ Yep.. That's what we're going to do next. I'm just glad he's not blaming me for this. It's not like I did anything.. I mean I chose to take on this project so....

What are the odds that the converter box is messing with things? he said the lights worked amazing for 50'. They were very bright then he lost everything except the 4 ways. -Truck and trailer... I mentioned I think it's the trailer. So we're going to hook it up to mine next. I have a stock 6 round plug I didn't notice was there..


I wired the converter box (for just the lights.. basically a 4 way flat) this way to his 7 blade style. I have the 6 round on the right. Shouldn't be anythign wrong here, right?
https://www.etrailer.com/Merchant2/g...u40277_800.jpg