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.
Product Page this Question was Asked From
Roadmaster 4-Diode Universal Wiring Kit for Towed Vehicles - 4-Way Flat Connectors
- Flat Tow Wiring Harness
- Splices into Vehicle Wiring
- Diode Kit
- Universal Fit
- 4 Flat
- Roadmaster
more information >
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on Flat Tow Wiring Harness
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