Why Won't 6 Diode Tow Bar Wiring Kit Work on 2025 GMC Sierra 3500

Updated 12/18/2025 | Published 12/17/2025

Question:

How do you wire a 2025 GMC 3500 Denali to be a tow vehicle? Ive tried to use the 6 diodes wiring schematic with no luck, then tried to use the smart diodes and still no luck. Any help would be greatly appreciated. Thank you.

asked by: Guy S

Expert Reply:

Hey Guy, have you tried wiring it as a 4 diode setup? Everything we have for your truck at this time is 4 diode which I believe is your issue. To do a 6 diode setup you'd need to have the turn signals separate from the stoplights and it doesn't look like your truck has amber lights from the pictures I looked up of it online.

expert reply by: Jameson C

Guy S.

12/18/2025

Hey Jameson, Thanks for getting back to me I called ROADMASTER and they said to wire it as per document 85-64444-04 08-25 That requires the use of the 6 diodes. I will try the 4 diode setup if that's what you think will work. Thanks Guy S