AUX switch install

C_Hag183 · May 22, 2025

Just realized that came off kinda douchey

not intended at all

Cheers!

SwitchBladeSierra · August 12

Hello, wondering if anyone can help me with this little problem. I was trying to order the Upfitter Switch that has TC, Cargo Light, Blank, Aux 1-4.... Order was cancelled due to "not having it". The only available option to me now is the Upfitter Switch that has all these options, but in the blank space there is "Exhaust Braking". My truck is a gasser, so this is of no use to me.

I need to find where Pin 4 and Pin 5 of the X2 connector run to (i.e X61A - X1 - Pins X & Y), and manipulate that somehow to get my desired outcome. Has anyone done this? Would there be any implications with me just doing nothing with it and installing it as is and never using it? I have gathered that it is "momentary" - so there are some considerations there.

Please help!

Edited August 12 by SwitchBladeSierra

SwitchBladeSierra · August 14

On 8/12/2026 at 6:09 PM, SwitchBladeSierra said:

Hello, wondering if anyone can help me with this little problem. I was trying to order the Upfitter Switch that has TC, Cargo Light, Blank, Aux 1-4.... Order was cancelled due to "not having it". The only available option to me now is the Upfitter Switch that has all these options, but in the blank space there is "Exhaust Braking". My truck is a gasser, so this is of no use to me.

I need to find where Pin 4 and Pin 5 of the X2 connector run to (i.e X61A - X1 - Pins X & Y), and manipulate that somehow to get my desired outcome. Has anyone done this? Would there be any implications with me just doing nothing with it and installing it as is and never using it? I have gathered that it is "momentary" - so there are some considerations there.

Please help!

For anyone following, this is what I have deduced from this forum - and my very specific niche case. Please do let me know if you see me going in the wrong direction here. For context, I have a 16 sierra 1500 w/t. Has TC and Cargo light switches. Removed the switch to find the X1 and X2 of the S48A connection populated with wires (x1 10-14, and x2 1-5).

Took photos of the X61A-X5 to find the wires from S48A-X1 land here at their respective pins (10, 11, 17, 23 on the X5). Was hopeful that this means my X51A fuse box has the appropriate pins... No cigar. So now I will be routing wires from the rear of the X61A-X1 to the engine bay and to their respective negative relay triggers. Please see to the diagram. If any has insight as to where the S48A-X2 pins 4 and 5 land that would be awesome.

Will be attempting this sometime shortly and will likely make a youtube video out of it.

Note: please disregard fuse sizes. Main fuse will likely be 25A, all mini bus fuses will likely be 10-15A.

Here is my parts list:

GM 84347199 - TC, Cargo Light, Exhaust Brake (useless to me unless I find a means to reconfigure), Aux 1 - 4.
12V 6 Way Pre-Wired Fuse Relay Box Kit with 4 x 40A 4-Pin Relays (link below - some mods required to make negative trigger)

https://www.amazon.ca/dp/B0F4KCS43B?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

Various wire sizes (12 AWG - red and black, 14 AWG, 16 AWG multi-colored bundle)
Wire termination leads for X61A-X1 (unknown at this time)
Crimp connectors/Soldering Gun
Heat Shrink
Split Wire Loom

To be continued...

Cheers

Edited August 14 by SwitchBladeSierra

SwitchBladeSierra · August 19

On 8/14/2026 at 12:24 AM, SwitchBladeSierra said:

For anyone following, this is what I have deduced from this forum - and my very specific niche case. Please do let me know if you see me going in the wrong direction here. For context, I have a 16 sierra 1500 w/t. Has TC and Cargo light switches. Removed the switch to find the X1 and X2 of the S48A connection populated with wires (x1 10-14, and x2 1-5).

Took photos of the X61A-X5 to find the wires from S48A-X1 land here at their respective pins (10, 11, 17, 23 on the X5). Was hopeful that this means my X51A fuse box has the appropriate pins... No cigar. So now I will be routing wires from the rear of the X61A-X1 to the engine bay and to their respective negative relay triggers. Please see to the diagram. If any has insight as to where the S48A-X2 pins 4 and 5 land that would be awesome.

Will be attempting this sometime shortly and will likely make a youtube video out of it.

Note: please disregard fuse sizes. Main fuse will likely be 25A, all mini bus fuses will likely be 10-15A.

Here is my parts list:

GM 84347199 - TC, Cargo Light, Exhaust Brake (useless to me unless I find a means to reconfigure), Aux 1 - 4.

12V 6 Way Pre-Wired Fuse Relay Box Kit with 4 x 40A 4-Pin Relays (link below - some mods required to make negative trigger)

https://www.amazon.ca/dp/B0F4KCS43B?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

Various wire sizes (12 AWG - red and black, 14 AWG, 16 AWG multi-colored bundle)

Wire termination leads for X61A-X1 (unknown at this time)

Crimp connectors/Soldering Gun

Heat Shrink

Split Wire Loom

To be continued...

Cheers

Update for anyone following:

Installed everything as shown in diagram. Opted for 8 AWG from Battery Positive to a 50A resettable inline breaker. 8 AWG is tied into to 2x 12 AWG wires feeding a 6 way fuse bus in parallel (manufacturer’s design of what I purchased).

4 of the 6 fuses available for circuits are tied to terminal 30 of each relay. I tied a jumper from one of my spare circuits off the bus to terminal 86 of each relay. The trigger, terminal 85, was pulled from my interior by way of T-Taps from the X61A-X5 pins 10, 11, 17 and 23. This was the hardest part of the job. Even with the X61A unbolted and the X5 removed - there was VERY little wiggle room.

I added back up lights that I want to come on with my cargo lamp - but when I would check continuity between S48A-X1 pin 18 to its respective landing point on the X61A-X5 it triggers the factory relay… Instead I opted for a add-a-fuse on the passenger interior fuse panel (fuse location 10 - cargo lamp) and ran it through the boot on the driver side to my load. Did this to avoid introducing any electrical gremlins.

Note: Please check for continuity between the S48A-X1 and the X61A-X5. In my case wire colours were not the same as other’s who have posted. To do a continuity check you need a Multimeter. Completely disassemble the S48A-X1 and remove the brown face plate off the X61A-X5 by way of a flat head screwdriver - this was the only way I could get any results.

The outputs, terminal 87 of the relays, were fed into a junction box and landed at Individual studs and were labelled Aux 1-4.

At this point, all you need to do is run wire to your loads and bring them to ground. I created a negative bus in the engine bay, all my negatives land here.

For anyone having issues with all of your new aux switch lights coming on with the press of one - I noticed this only to be an issue when the battery wasn’t hooked up to my relays? No idea why, but it was quickly corrected by having my system buttoned up and functional.