Does the black wire go to the battery positive and the ground side of the battery go to the frame. [b]What is the yellow wire for?
Yes, the Black wire goes to the Battery Positive. Since I'm a Belt-AND-Suspenders sort of guy, I connected the Negative Battery terminal to the trailer frame PLUS the White wire in the trailer connector.
The most common use for the Yellow wire is to activate [b]Back-up Lights
on the trailer if you have them. Some
factory harnesses are pre-wired this way on the tow-vehicle end of the connector.
Top Bulb = Yellow Wire