4.3 to 5.7 swap - No Brake Light Relay/ Fuse on swapped Harness

[Jglew82]

So how do the lights work without a relay?
Also where can I test to see if the switch is actually working on a suburban?

The answer you need is in the diagram I posted. Battery power comes into the brake pedal switch, and then out to the multifunction switch and then out back to the lights when the pedal is depressed. Test for battery voltage coming into the switch on the orange wire, and test for battery voltage when the pedal is depressed on the white wire.

 

[Kory Dowell]

The answer you need is in the diagram I posted. Battery power comes into the brake pedal switch, and then out to the multifunction switch and then out back to the lights when the pedal is depressed. Test for battery voltage coming into the switch on the orange wire, and test for battery voltage when the pedal is depressed on the white wire.

I'll check today, the brake lights never really work since I got this thing but being a backup farm hunting deal never worried much about it.

I have all my lights including turn and night lights. What I dont understand is on one harness in the back I have 2 brown and a black. Assuming black is ground I don't know what the 2nd brown is for. Thanks for your help.

 

[Jglew82]

I'll check today, the brake lights never really work since I got this thing but being a backup farm hunting deal never worried much about it.

I have all my lights including turn and night lights. What I dont understand is on one harness in the back I have 2 brown and a black. Assuming black is ground I don't know what the 2nd brown is for. Thanks for your help.

Brown is your running lights/clearance lights/tag lights.

 

[Kory Dowell]

Y

Brown is your running lights/clearance lights/tag lights.

Yea but the harness leading to my lights i have the normal green light green yellow and the 2 browns and 1 black

 

[Jglew82]

Y

Yea but the harness leading to my lights i have the normal green light green yellow and the 2 browns and 1 black

There are splice packs in the rear for the browns where they split off to the above mentioned fixtures (park lamps, tag lights, clearance lights if equipped, and trailer wiring breakout). All browns go to lights activated by the parking lamp circuit.

 

[Kory Dowell]

There are splice packs in the rear for the browns where they split off to the above mentioned fixtures (park lamps, tag lights, clearance lights if equipped, and trailer wiring breakout). All browns go to lights activated by the parking lamp circuit.

Ok I just couldn't understand why there was 2 going to the tail lights when probing with 12v one brown wire activates both lights. Gonna check the switch after work.

 

[LSstepside96]

There are splice packs in the rear for the browns where they split off to the above mentioned fixtures (park lamps, tag lights, clearance lights if equipped, and trailer wiring breakout). All browns go to lights activated by the parking lamp circuit.

There are splice packs in the rear for the browns where they split off to the above mentioned fixtures (park lamps, tag lights, clearance lights if equipped, and trailer wiring breakout). All browns go to lights activated by the parking lamp circuit.

The Suburban doesn't use a relay - it get's power from the instrument panel 20a stop fuse, to the brake/tcc switch, and up to the multi-function switch and out to the lights. You will need to figure out how to wire in a relay (since that is how the truck wiring was designed) or run the white wire from the brake pedal switch directly to the multi-function switch to power the stop lights (you could tie in where the truck relay used to feed the multi-function switch).

There's a splice pack from the brake switch with a leg to activate the relay on trucks, but on the SUV, it just omits this path and heads right for the switch. It's going to take some wiring work for sure, but it is doable. If I were you, I would try to pin the fuse block or use the truck fuse block if at all possible. Here's a quick and dirty diagram. Yellow is Sub, red is truck.

You should be able to make it work without TOO much grief. If you can swap the drivetrain, you got this!

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jglew82 your the wiring harness Guru I have been looking for lol thank you for posting this and explaining it so good. Here is the problem I'm having I swapped a 97 suburban motor and trans with the wiring harness intact, did not remove from engine or trans, the question is will the engine harness work with a 98 truck dash since I installed it in a k1500 truck, the motor from the sub was a 454. Because I have no brake lights but you explained why and thank you for that, plus my amp, coolant, oil pressure all act crazing when I turn the lights on or put the truck in gear or turn the turn signals on. checked all the grounds and even add some still the gauges act all erratic. the rpm and speedo work ok. Any thoughts what the problems could be would be greatly appreciated.