Ok guys, yet another darn wiring conversion question. I have a 1985 Ford F-250 Diesel which has the stock Class 3 Hitch and stock 4 Wire Flat trailer wiring harness connector. I have always used 4 wire connector type trailers, but I am about to buy an 18' Bri-Mar Full Deck Car Hauler and it has a 7 RV Blade round connector on it. So today I purchased a Hopkins Towing Solutions Multi-Tow 7 and 4 Model 47185 Trailer wiring harness kit.

It allows you to keep an open 4 Wire Flat and a 7 RV Blade. I have not hooked up the 3 new wires that comes with it yet (Reverse, Power, or the brake wire). I hooked up the 4 Wire connector and the new ground. I hooked up my 4 Wire trailer to it and all the lights are fine with the standard 4 wire connector, however I hooked a round 4 flat connector converter from my 4 Wire trailer connector to the 7 RV Blade, and then none of the lights worked anymore. I know that was confusing.

So my question is, does the wiring harness have to have the power wire connector hooked up for the 7 RV Blade to work the lights & signals? I will hook up the reverse, brakes, and power wire later, but for now I just want the lights to be able to work when using the 7 RV Blade.

Any ideas?

Here are some pics of the new set up.

 

I would just wire the 7 wire RV connector to the truck wires and get a 7 to 4 flat adapter.

Good luck.

 

The 7 way RV connector is not powered. Meaning the power wire is meant as a hot circuit, generally for charging the RV's on-board batteries.

Since the 4 way flat connector does work when you have it hooked up I would venture to bet that the adapter isn't working correctly. You will also want to make sure that your ground (the white wire in the picture) is good. I suggest a self-tapping/drilling screw. Relying solely on the hitch/hitchball/coupler for a ground is asking for wiring gremlins to visit you

 

don't they make a 7 pole that just plugs into existing harness, so there are no splices? 7-4 & 7-5 adapters are available. just wondering?

 

Since it is an 1985 model you would have to use a litemate, which is probably how he already has an existing 4 way.

 

Well I was able to pick up my new trailer today. I also tried to work on the wiring and of course it still doesn't work. I called Hopkins today and they said if the 4 Flat Wire is working the brakes, lights, and turn signals, then there is something wrong with the 7 RV Flat. So they told me to exchange it with a new one. Well I did that this evening and the same thing is happening, still no freaking lights except for the left rear blinker and the left rear brake light on the trailer. Nothing else works. This is driving my >>>>ing crazy.

I am really good at wiring, and I can't even figure this mess out. I am pissed.

 

How to Wire your Car or Truck for Trailer Lights
Check this place out. It may help.

 

Yea, that is a great site. I have looked at that in the past and it is very helpful. This is how my trailer is set up, but I think that the truck side and or the switch is wrong somehow. If I had any hair to pull out, I would be tearing it out right about now.

 

I give up. I just removed the entire set up, drilled a new ground on the frame and sanded the entire surface. This time I had stronger current at the tester on the 4 prong, but once I hook that damn 7 RV up to my trailer only the left rear blinker is working. This is freaking crazy.

I am going back to the trailer shop early tomorrow morning and have them rewire the entire damn thing including the brake controller, reverse, and the 12v power wire.

 

Just to close the loop on this, I spoke with a local RV shop, and the service mentioned to check the prongs to make sure they are actually contacting each other on the trailer side and on the truck side. Sure enough, they were not even touching each other. I had to pry the truck side prongs out about 1/8" each for them to make contact with the trailer side plug. Now everything works perfectly. I knew it was going to be something stupid like that.

Now I am much happier.

 

I find that it is very easy with the 7 pin plug to think you have the plug pushed all the way in, only to find out that it isn't, and if you give it another good push it'll "pop" in the rest of the way.