Electrical Question at Trailer wiring...

[BlackDawg]

I have a 2003 Silverado 1500HD Crew Cab 4x4 with factory trailer "stuff".

 

I was just inspecting the receptacle plate for plugging in a trailer wiring plug as I have to purchase or build a converter so that my 4 wire trailer plug will have something to plug into.

 

I noticed that behind the plate (in addition to all of the trailer and brake wires) is a single light blue wire with a weatherproof cap.

 

Anybody know what that wire is for?

[builderpaul]

On my 04 that wire is for the center mount brake light on the trailer.

[GM-Tech]

Dunno if you have the standard or "heavy duty" trailering package, so here's both...

 

The six-wire harness contains the following trailer circuits:

 

Yellow: Left Stop/Turn Signal

Dark Green: Right Stop/Turn Signal

Brown: Taillamps

White: Ground

Light Green: Back-up Lamps

Light Blue: Center High-Mounted Stoplamp (CHMSL)

 

 

The eight-wire harness contains the following trailer circuits:

 

Yellow: Left Stop/Turn Signal

Dark Green: Right Stop/Turn Signal

Brown: Taillamps

White: Ground

Light Green: Back-up Lamps

Light Blue: CHMSL

Red: Battery Feed

Dark Blue: Trailer Brake

[BlackDawg]

Dunno if you have the standard or "heavy duty" trailering package, so here's both...

 

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Thank you for your reply!

 

I have a 7-blade receptacle (including the core contact) but the harness I have has 8 conductors in it so I guess that makes it the heavy-duty one you refer to.

 

I must add that I was impressed when I first saw GM's receptacle plate as it actually indicates which contact operates what! Nowhere on the plate does it indicate CHMSL so that aligns with your reply. That and the fact that standard wiring for the 7 conductor plugs and receptacles were designed prior to the introduction of CHMSLs so it would naturally stand on its own.

 

The wires I have are:

Black. I expect this is the “white” ground wire you refer to (it is a heavier gauge than the rest).

Yellow, Dark Green, Brown, Light Green, Red and Medium Blue (all similar gauge).

Light Blue (lighter gauge than all the rest).

 

The two blue wires are very similar in shade, perhaps because of fading near the end of the harness sheath.

 

Thank you again for your reply!

[BlackDawg]

On my 04 that wire is for the center mount brake light on the trailer.

 

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Oops, timing problem...thank you also for your reply, most appreciated!