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

[John P]

My son has a '97 Silverado w/ 4.3L, we swapped it for a '98 Suburban 5.7L Engine and Harness, Now that its installed, Runs good, but we have no brake lights, all other lights work just fine (Parking/ Reverse, etc). Comparing our original Silverado Harness/ Fuse Box to the swapped Suburban Harness/ Fuse box, it looks identical but the Suburban has the cutouts for the Brake Relay and Fuse in the under the hood Fuse box, but it don't have the pins in it like the Silverado Fuse box does. Anyone run into this issue and have a fix for it, without having to reinstall the original V6 harness and mod it for a V8.
Curious how the Suburban had Brake lights unless they had a relay/ fuse mounted elsewhere.

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[John P]

Any help on this?

 

[Jglew82]

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!

*edited for formatting and words

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[John P]

Thank you for taking the time to respond and attach the diagram. Just my luck I use a Harness/ Fusebox with No Brake Relay out of the thousands out there. Surprised no one had mentioned this before as I couldn't find any info regarding that issue on a swap. Very much appreciated.

 

[Driven by Gears]

im doing this same swap on mine and i ran into the same issue this is what i did check out www.youtube.com/drivenbygears for my videos. I put back in the factory v6 wiring that cam with my truck and just extended the v6 wiring for the knock sensor and the sensor on the left side of the engine.

 

[Driven by Gears]

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[Jglew82]

@Driven by Gears that's awesome info! Side note, for some reason I can't view that video, even when I visit your channel directly. Your others seem to work just fine.

 

[Driven by Gears]

@Driven by Gears that's awesome info! Side note, for some reason I can't view that video, even when I visit your channel directly. Your others seem to work just fine.

realyy that is weird

 

[Driven by Gears]

i see that now for some reason it is not even working 4 me so i reported it to youtube hopefully it will come back up

 

[Kory Dowell]

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!

*edited for formatting and words

You must be registered for see images attach

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?