I just got finished installing a pair of Aux. backup lights on my truck, triggered off the cargo lamp. Now, seemingly at random, the lights will stay on/come on regardless of the cargo light being on.

I used the cargo lamp wire off the under-dash panel (c3-D) and a normally-closed relay (gp sorensen MR76) to trigger the lights. Everything is on a good, common ground.

HELP!!

see this link here (http://dieselplace.com/forum/showthread.php?t=12784&highlight=cargo+light+back) , don't know if it will help but it talks about the cargo light being a negative connection. I hooked my back-up lights to a seperate switch.

I didn't insulate the light brackets from the bumper/frame but since I used a relay instead of directly wiring the lights to the cargo light I didn't think I needed to.

Is that where I F-ed up???

The cargo lamp is ground controlled. c3-d is the ground side of the cargo lamp but before the switch and BCM control. c3-d will have 12v whenever inadvertent power supply is supplied by the BCM. A seperate switch would be the easiest way to make them work properly.

I understand that it would be easier to simply wire the lights seperately, but the cleanliness of having them on the cargo lamp switch is pretty critical to me.

I know plenty of guys have made this work . . . there has to be something simple I've overlooked.

Maybe if you used c3-d as a ground control for your relay with a diode in it so it doesn't backfeed into the inadvertent power supply circuit.

On second though, maybe this will work with a normally open relay for your lights. Add a diode so your lights don't come on when the reading lights are on.

What type of diode do I need? Are there different ones? I've never screwed with them before.


Thanks!!

That I don't know. Maybe someone else with electrical knowledge can help out here.

Try a 1N4001 or a 1N4004. Either should do the trick.

ok, so I can put either of those in the C3-D wire then use it as a ground for my relay and it *should* work, correct???

The diodes work great.

I soldered one in and all my lights come on with high beam.

Boy that diagram hurts my head. I insulated the brackets for the lights. If it is making contact with ground they will stay on. I used some garloc material between the brackets and the bumper and I also used the nuts thats are incased in rubber and expand when threaded into and tightened up or you could also use the white square plastic lock nuts that come with the hood bug shields.

I've got a spare set of MSD anti-vibration mounts that I think are non-conductive. (need to throw the Fluke on them in the morning) I was going to try those first just to see. If it's still busting my balls, I'll throw some diodes at it and do a little re-arranging. If it STILL doesn't work, I'll pull the little suckers off and stick w/ my Maglite. :D

Thanks for the help everyone!!

Why not just wire in a relay and use the negative trigger for the cargo light for your backup light trigger? You could then also wire the lights directly to the existing back up lights too. then it would be auto and manual...

How would you accomplish that? Isnt the relay positive triggered?

Need to be more specific...

Why not just wire in a relay and use the negative trigger for the cargo light for your backup light trigger? You could then also wire the lights directly to the existing back up lights too. then it would be auto and manual...


hay blueox could you draw a wire diagram for this set up? this is just how I am wanting to do minebut have not figured out how to do it yet. and is the trailer backup wire in the back big enough to run two 55 watt lights?

Finally figured my junk out . . . I had the 12v power running from the trailer harness (too lazy to run two wires from the under-dash panel). Explains why my lights would "mysteriously" come on exactly 10min after closing/locking up the truck. :rolleyes:

Turns out the truck shut power off to my "switched" wire but since I still had 12v constant from the trailer harness, it triggered the relay. By taking power from the box under the dash (C3-M) the 12v constant would shut off at the same time as the switch now . . . .

Frikkin' GM engineers . . . . don't they know some of us good 'ol boys still like to work on our own vehicles ???

Okay, here's what ya do. Get a relay and some wire, at least 18 gauge, and a relay.
Relay to BCM
Connect terminal 85 and 30 to C5 pin D
Connect terminal 87 to C5 pin F
Connect terminal 86 to C4 pin A6

This will make your back up lights come on any time the cargo light is on. You can add a switch between T86 and C4 pin A6 to have it selectable.

You shouldn't have any problems adding lights to the regular back up light circuit (light green wire) at the rear of the truck since it's designed to power trailer back up lights too.

If you think you need more power for your add on lights in the rear you can add another relay at the rear of the truck.

Here's the connections

You should use a 10 amp fuse for this.

Relay to trailer connector
T30 Pin E (red)
T85 Pin a (light Green)
T86 Pin B (black) or ground
T87 +power to add on back up lights

If you don't want to cut into your trailer harness, you can ger a connector that adds a universal trailer plug....Some Masshole taught me that...

Ox

I guess my only problem is what and where is the BCM and and C5 & C4 ?


Okay, here's what ya do. Get a relay and some wire, at least 18 gauge, and a relay.
Relay to BCM
Connect terminal 85 and 30 to C5 pin D
Connect terminal 87 to C5 pin F
Connect terminal 86 to C4 pin A6

This will make your back up lights come on any time the cargo light is on. You can add a switch between T86 and C4 pin A6 to have it selectable.

You shouldn't have any problems adding lights to the regular back up light circuit (light green wire) at the rear of the truck since it's designed to power trailer back up lights too.

If you think you need more power for your add on lights in the rear you can add another relay at the rear of the truck.

Here's the connections

You should use a 10 amp fuse for this.

Relay to trailer connector
T30 Pin E (red)
T85 Pin a (light Green)
T86 Pin B (black) or ground
T87 +power to add on back up lights

If you don't want to cut into your trailer harness, you can ger a connector that adds a universal trailer plug....Some Masshole taught me that...

Ox

It's the black box under the steering column.

OK thanks I FINALY found it. I feel like a dumb a$$

OK i am totaly confused, I found the BCM and found the C4 & C5 plugs
but there is only two wires going into each oue of them, and My C4 does not have a A6 pin. WTF I am starting to feel like a real dummy here. can anyone help Me out here? is this a picture of the right place?
http://207.53.239.181/~terry/truck/Backup-lights/IP-RelayBlock.jpg



Okay, here's what ya do. Get a relay and some wire, at least 18 gauge, and a relay.
Relay to BCM
Connect terminal 85 and 30 to C5 pin D
Connect terminal 87 to C5 pin F
Connect terminal 86 to C4 pin A6

This will make your back up lights come on any time the cargo light is on. You can add a switch between T86 and C4 pin A6 to have it selectable.

You shouldn't have any problems adding lights to the regular back up light circuit (light green wire) at the rear of the truck since it's designed to power trailer back up lights too.

If you think you need more power for your add on lights in the rear you can add another relay at the rear of the truck.

Here's the connections

You should use a 10 amp fuse for this.

Relay to trailer connector
T30 Pin E (red)
T85 Pin a (light Green)
T86 Pin B (black) or ground
T87 +power to add on back up lights

If you don't want to cut into your trailer harness, you can ger a connector that adds a universal trailer plug....Some Masshole taught me that...

Ox

yes thats the right relay block. i didnt trace the method someone above posted, but if you look at the thread from a few weeks ago, you will see my step by step instructions. i used the C3 plug if i recall right. mine work perfectly.

Why can't you just wire them into the existing back-up light wires? That way they will come on when you engage reverse, no???

yes but I also want them to come on when I turn on the cargo lights

Why can't you just wire them into the existing back-up light wires? That way they will come on when you engage reverse, no???

Why can't you just wire them into the existing back-up light wires? That way they will come on when you engage reverse, no???
yes, if that was your desire. i didnt want mine to blind everyone in the parking lot, but wanted to be able to turn them on with the truck parked so i can load my boat going hunting in the morning. all depends on what your uses are.