Yeah I know it has been discussed before but I could'nt find it in my search so I apologize in advance. Here is the situation.....I had the same wiring harness installed on my motor home that is on my truck, never had any problems backing my boat up when it's hooked up to the truck but when it is hooked up to the motor home it won't back up and the back up lights are coming on so I'm not sure why it's not disengaging the brakes.

what about if you disconnect the harness? does it back up then? if so, then you might have a short somewhere on the motorhome?

Last plug on boat harness into first plug (next to opposite, not on the end) on RV harness is how you do it when you've got a 4-prong, try that and see if it works, if it does, you've got a mucked wire somewhere or your reverse lights aren't hooked into your tow kit properly.

First you have to find the wire that energizes when you put the vehicle in reverse. Get a $5 test light at pep boys and connect one side(usually an alligator clip) to the frame of the vehicle or even the trailer ball. Then(carefully) have someone put the vehicle in reverse and see if one of the wires becomes 'hot'.... by lighting up the test light. <BR> <BR>That's your wire you want to connect to the trailer lock-out.

When it's unplugged it wont back up either. The wiring receptor is the same round one that is on my f-150 do you think the one they installed on the motor home is faulty?

If you do a voltage check on the 5th pin of the motorhome it should be hot "12v" when the motor home is in reverse. If not it is wired incorrectly or there is a fuse blown. If it is hot the problem is with the solonid on the trailer but you said it works with your truck.

d dub, <BR>It should not ever work when it is disconnected. tony and hugh have your answer. I have one of those circuit testers I could bring out on wednesday and we could play around in the parking lot if you want... otherwise like huhg said go get a cheapy.... or easy way is go to uhaul and they will do it in 5 mins....

My trailer has a 5 prong harness but my truck is only a 4 prong harness. To back up, I have to plug the harness in backwards and turn on my lights otherwise the trailer won't back up. Could this be the same?

Ronia, you need a 5th wire plug on the truck that is connected to the back-up lights. When you plug in backwards and turn the lights on you are putting voltage to the 5th wire on the trailer plug. <BR> <BR>There is also a manual lockout on the side of the receiver that you should have a "key" for. It prevents the receiver from sliding back and locking the brakes when backing.

George, <BR>Yup, gotcha. ACtually it's easier to flip the wire than to try and find the "key".