adding factory aux beacon light switch

[042500HD]

I'm trying to add a factory aux light / beacon switch to my 04 2500HD with 8.1 and allison that does not have the factory snow plow prep rpo VYU option. I bought the switch and harness from gm and was just curious where the grey end of the harness connects to or if I need to wire it in myself. When I removed the blank cover and installed the switch their was an 8 cavity male plug tsped up in harness but it does not plug in to the 6 cavity connector. The only other thing I have plugged into the factory housing is the switch for the air bag. Any ideas?

[DmaxMaverick]

Looking at the diagram for 2001 (I don't have a 2004 diagram, but they should be similar), the switch and beacon are integrated into the underhood junction (fused and relayed), and the headlamp switch (dimmer for the button lamp). Check above the headliner for the beacon harness. If it isn't there, then the other (ends) won't likely be, either. My 2001 has the switch and beacon harnesses present, as well as live slots for the fuse and relay, although it does not have the plow option.

I have a good diagram of the beacon circuit for 01/02 models, but not later. If you think it may be helpful, I can email it to you.

[042500HD]

Thank you for the reply. I will check to see if I have the beacon harness above headliner tomorrow night as I'm up to my elbows in work right now. I do have the fuses present in the seo1 and seo2 slots as per the Chilton manual and I did not have to had them so I'll cross my fingers. Gm upfitters as well as the local dealers have not been any help on this issue other than getting the part numbers for the switch and connectors. I had first bought the 99-02 switch and connector because it had aux lights printed above button instead of the goofy beacon then I found the 8 pin connector and thought my switch was wrong so I ordered the one for my year with the connector hoping it would plug in. I would think I can make one of these setups work and sell the other one since they are non returnable.

[042500HD]

By the way if you buy the 99-02 connector it has all grey wire leads hanging from it and only has the one end on it as its used for seat heaters and alot of other items throughout those years of trucks.

[DmaxMaverick]

If you got the switch and/or harness for 99-02 trucks, it's the wrong one. That's for the GMT-400 trucks (3500, 3500HD, Chassis/Cab), not the GMT-800, like yours, which began for the 2001 model year, when no GMT-800 3500+ trucks were available. Typical GM transition year overlap.

[042500HD]

I currently have the 99-02 switch installed. It is for the new body style trucks and appears to have the same connection on back as the 03 -07 classic switch I just bought. It has the aux lights printed on it.