4 pin to 5 pin trailer lights

I am trying to hook up a four pin to 5 pin Trailer light connector. The fifth pin, the blue wire, hooks up to the reverse lights. On the truck. Can I just splice in to the wires inside the tail light, and if so, which wire do I spliced into that leads to the reverse light, or does it matter, can I splice into either one.

 

This is a picture of the reverse lights. The white and black wire and the red and gray wire or what run to the light. Can I splice into one of those and if so does it matter which one

 

One wire should be +12v and the other ground. I’d check with a multimeter on the socket which is connected to ground then tap into the other. Or check for 12 when in reverse. Should only take a minute to check.

 

When in reverse....with the engine off, parking brakes set and wheel chocked. Don't want to see any of our members getting a Darwin award.

 

Mind taking a picture of your truck harness connector at bottom of bumper and even the connector that has this blue wire you mention.
As a side note, 99.9 % if not 100% of wires that are white with black stripe on our trucks signify ground wire.

 

Red wire should be 12v+ in reverse

White with black stripe is ground — it’s the only color wire that goes to every light in the housing


The big question I have is can the reverse circuit handle the extra amperage of more lights without a relay???