Automotive Reference
What each wire does and which pin it lands on — for the 4-pin flat, the 5-pin, and the 7-pin RV blade. Labeled connector diagrams, not a wall of text.
The light-duty standard — lights only, no brakes or power. Four wires do everything.
5-pin adds one wire — usually Blue for reverse lights or surge-brake lockout.
The heavy-duty round connector: adds electric brakes, 12V power and reverse to the four lighting wires.
Pin layout is representative — always match by function, and confirm with a tester.
| Wire color | Function | 4-pin | 7-pin |
|---|---|---|---|
| White | Ground | ✓ | ✓ |
| Brown | Tail / running / marker lights | ✓ | ✓ |
| Yellow | Left turn & brake | ✓ | ✓ |
| Green | Right turn & brake | ✓ | ✓ |
| Blue | Electric brakes (brake controller) | — | ✓ |
| Black | 12V+ constant power (battery / aux charge) | — | ✓ |
| Purple | Reverse / backup lights | — | ✓* |
* 12V, reverse and aux colors are the ones that vary by brand — the lighting four are the reliable constants.
White is ground, brown is tail/running lights, yellow is left turn & brake, and green is right turn & brake. That's the flat-4 connector — the light-duty standard used on most small trailers.
Blue, on a 7-pin connector — it runs from your brake controller to the trailer's electric brakes. Black is the constant 12V+ power. Always verify both with a tester, since these are the colors that vary between manufacturers.
A 4-pin (flat) handles lights only: ground, tail, and the two turn/brake signals. A 7-pin (RV blade) adds three heavy-duty circuits — electric brakes, 12V power, and reverse — for larger trailers with their own brakes and battery.
Yellow is left turn and brake; green is right. Easy mnemonic: the colors are alphabetical with the sides — Green/right, and yellow takes left.