[Wisha Haddan H3]

Well I finally got around to it and spliced my compressor to the RV socket plug this morning. I could have used the center pin, but that's a keyed accessory terminal. I went with the 12v + accessory blade for constant power. I took my time and probably spent 30 min on it ... easy as pie.

1. Check the diagram on the trailer harness cover and verify which blades are which.
2. Test the blades with a voltmeter. The 12v accessory blade is at about 2 o'clock. The ground is directly opposite at about 8 o'clock.
3. Separate the terminal adapter from the plug housing, and mark power and ground on the corresponding terminals. RV plugs are directional, so matching the blades is important.
4. Cut the positive alligator clip and mark it with tape
5. Cut the negative alligator clip
6. Thread the plug housing onto the wires
7. Strip 1/2" off the positive lead, twist the strands and clamp to the adapter's 12v + terminal
8. Strip 1/2" off the negative lead, twist the strands and clamp to the adapter's ground terminal
9. **IMPORTANT** Insert the adapter into the plug housing and SECURE WITH SET SCREW. If you don't secure it, it will get stuck in the harness during step 10.
10. Plug assembled RV plug adapter into trailer harness and test compressor ... congratulations, you're done.

The compressor definitely runs better with a direct battery connection. I might mount it in the engine bay at some point, but this will work for now.