The OEM wire routing would go from the S48A (switch panel) to the X61A, X4connector(Junction box behind brake pedal) then out of the X61A, X1 connector, and into the X50A, X3 & X4 connectors (under hood fuse box) your accessory power or output from the relays will come out of the X50A (fused) and back into the X61A, X1 connector and out of the X61A, X7 connector. These pictures show the routing in and out of the X61A junction block behind the brake pedal. Please note: in Gm Upfitter there is a discrepancy between 2015 and 2016 model years pertaining to where the wires from the S48A (switch) land at the X61A (junction box). They land in either Connector (X4 or X5). Simply verify by checking the location and color of neighboring wires to be sure you’re on the right connector. This may be due to a type-o or different wiring on different model years. .......still sorting that out.
@WesternMike can you snap a picture of your underhood fuse box, specifically where Upfitter relays 1-4 would plug in. (#60,61,62,65) I want to see if the pins are present for the relays. ( if it’s just a blank cavity or if there’s a metal pin inside to contact a relay)
Ok, this is good! Pins 10-13 are already wired so you’re in luck. These wires go to the X61A junction block behind your brake pedal on the firewall. They plug into the X1A-X5 connector (on the lower right) and come out the (X61A-X1 connector (firewall side behind X5) from there they go up to the under hood fuse box (X51A).
@csjumper2003 The TC & Cargo wires stay where they are. on the plug for the X2 connector you would cut the wire for pin number 4 to run to your air horn relay. You don’t necessarily have to cut the wire from #4 meaning you can just strip back some of the insulation and attach another wire to it. This wire (X2 #4) is the signal wire from the CNG switch. This plug that is there at the X2 connector is not doing anything in your application. It should have 6 wires in it and they aren’t doing anything so yo can use them (at least the one going to X2 #4) without worry. The link I provided is for a wire with a terminated lead meaning it’s a wire about 1.5 feet long with the terminal needed for the X1 connector factory crimped on the end of it. (Pigtails) (order 4 of them) you can open up your X1 plug and insert these wires directly into cavities 10,11,12,13 and then close the plug back up. Your X1 plug will then plug back in to the X1 opening with 4 new wires coming out (from Aux 1-4). These are your constant on/off negative signals from Aux 1-4.
I assume your truck has a gas motor? if so then the X2 plug doesn’t need to be used. I’m guessing you got the upfitter switch with TC,Cargo, Aux 1-4? does your X1 harness have any wires coming from pins 10-13?
Here is the back of your new “Upfitter Switch” from eBay. The smaller socket (X2) is where the Exhaust Brake or CNG plug if you had that would plug into. Although you never had either of those options you may very well have the harness sitting there plugged into a blank socket in the X2 position. You can plug this harness into the new “Upfitter Switch” from eBay and use the wire that goes to pin number four in that X2 connector. PIN number four in the X2 connector is the one coming from the CNG button and it is a momentary negative signal. This can be used to trigger a relay for your air horn since it only sends a signal while you’re pressing the button. The other switches send send their signal through the larger X1 connector (18 position). Pins 17&18 are your traction control signal and your cargo lamp signal. (Both are momentary negative signals) These signals go to the BCM and tell it to do what it does. Your ”Upfitter” or “Aux” switches use pins 10 through 13 (10,11,12 &13). These switches send their constant negative signals through these pins. Your harness that is plugged into X1 will likely not have any wires occupying pins 10-13. You will have to add these wires (13575782) https://www.gmpartsdirect.com/oem-parts/gm-f--s-wire-13575782 these wires can be used to trigger 4 different relays in your under hood fuse box X50A or 4 relays from BFE Amazon or eBay wherever. They send a negative signal until you press the button again.
Yes, the momentary would work for that. You could also open one of the Auxiliary switches and remove the little “j” shaped spring and make it a momentary switch. I’ll take a picture of that next time I get to the work bench. It’s pretty easy though.
Most OnlineNewest Member
Who's Online 78 Members, 2 Anonymous, 376 Guests (See full list)
- Jamie Whitley
- Retired Bob
- CR Rodgers