7 pin trailer wiring help?

[GrantP]

I have a small RV trailer that uses the "RV Industry Standard 7 way" connector. My issue is that if I leave the battery on the RV connected and I plug in the 7 pin harness to the truck, the reverse lights light up on the truck. I have verified that the center/round pin on the trailer is hot with the battery connected. I've got around this problem in the past by just disconnecting the RV battery but I'd like to get to the bottom of it. The center pin according to the manufacturer (starcraft) is the "charge" wire but on the truck it is the reverse lights. Do I need to rewire the trailer plug? Is it normal to have to do so?

More background info, I've had this trailer on both of my trucks in my sig and it behaves the same. Also if I leave the trailer plugged in to the truck overnight it will completely drain the batteries, after I lost two optima's I always disconnect it when not driving. I think that is a separate issue though.

Thanks for any help!

 

[RustyJC]

The industry standard is for the center pin to be AUX or (typically) back-up lights where they are used. B+ is pin #4 - see HERE for the industry-standard Pollak 7-pin connector wiring. The trailer battery is backfeeding your truck's back-up lights.

Rusty

 

[GrantP]

Thanks Rusty. Pin 4 is not hot with the battery connected but it seems to me like it should be? The center pin has a heavy gauge black wire to it, much heavier than the black wire to pin 4. I'd like to be able to leave the battery connected so the truck can charge the battery while driving. Do I need to move the wire from the center pin over to pin 4? FWIW, the trailer does not have reverse lights.

 

[RustyJC]

You need to wire the trailer plug exactly like the one shown on the e-trailer link I provided. Check every terminal to ensure that it's correct, as it sounds like Starcraft didn't know what the convention was or, if they did, for whatever reason they chose not to follow it. Either that, or perhaps a previous owner rewired it to conform to his miswired tow vehicle. Regardless, I can guarantee you that the truck side of the plug came from Dodge wired as shown - every one I've owned has, at least.

If the trailer has something other than B+ attached to pin #4, that's what is drawing your truck battery down as the truck side of the plug has B+ on pin #4.

Rusty

 

[GrantP]

I just used a fused jumper wire to check all the lights and all are correct with the exception of the center pin and (maybe) pin 4. I can trace the center pin wire all the way back to the RV battery so as you mentioned the battery is backfeeding my reverse lights. Pin 4 does not go to the battery, it runs along the framerail and inside the RV. The owners manual says pin 4 is for interior lights/accessories and should be connected to the truck battery, the center pin is the "charge line" and should be connected to an isolator on the truck. The only modification to the trailer wiring looks to be the addition of a break away kit otherwise it appears to be unmolested.

So it sounds like pin 4 is the culprit for the dead batteries...something inside the camper is pulling a lot of juice to completely kill two optimas overnight. I'll have to figure out how to isolate the offender later.

The question now is what to do with the center pin "charge line"? It's obviously not working as intended since it's lighting up my reverse lights instead of being connected to B+ on the truck. I'm thinking I need to swap pin 4 and the center pin.

 

[RustyJC]

Why should the truck battery power the trailer's interior lights and accessories? These should be powered by the trailer's battery from its B+ terminal through a 12VDC fuse block in the trailer.

From what you're describing, the B+ wire from pin #7 (the center pin) should be moved to pin #4, and the wire that is now on pin #4 should be moved to the positive (B+) side of the trailer battery, ensuring that appropriate fusing is in place between B+ and the load(s). It sounds like you have a substantial phantom load in the trailer, so if you leave the truck plugged in, you risk running both the truck and trailer batteries down when the truck isn't running. If the trailer is disconnected and not plugged into shore power, it will run the trailer battery(ies) down unless you have a "salesman's switch" (a battery disconnect switch) installed to disconnect the B+ terminal of the trailer battery(ies) from the trailer when not in use.

Rusty

 

[Wingate]

seems like there are TWO TYPES of 7 way RV plugs. Cant remember if they are called type 1&2 or Type A&B...
ran into this when I hooked the 06 to a borrowed gn trailer. Put the truck in gear and the trailer brakes locked up!.

 

[RustyJC]

You're thinking of the 6 or 7 pin round pin plug, I believe. Unlike RVs, gooseneck wiring isn't as standardized. Very often, battery and brake wires are swapped - so often that many 7 blade Pollak adapters to the 6/7 round have a switch or jumpers to swap these 2 wires.

Rusty

 

[GrantP]

Why should the truck battery power the trailer's interior lights and accessories? These should be powered by the trailer's battery from its B+ terminal through a 12VDC fuse block in the trailer.
Rusty

Giving this a little more thought..Pin 4 in the manual says it's for the interior/acc but it must be connected to the RV battery. I can disconnect the truck and still use lights etc inside the camper. I have two wire connections to the RV B+ terminal, one clearly goes directly to the center pin, the other comes from inside the trailer. I can't trace the whole wire but it looks like it goes from the 7 pin harness and into the trailer and then comes back out to the battery +. I don't have continuity between pin 4 and this wire so that needs further investigation. Am I wrong that pin 4 should be hot with the RV battery connected?

 

[RustyJC]

Yes, pin #4 on the trailer side feeds straight to the trailer battery B+ and will always be hot barring a blown fuse or the battery isolator switch being turned off.

Rusty

 

[jelag]

Some of the trucks have this the pin out printed on the cover of the plug.... my trucks doesn't have it but my Jeep does... I finally printed the sheet and put it in the fuse panel under the hood until I committed it to memory.... I can't tell you how many of my coffee buddies have trucks, trailers, that don't conform... and we've been trying to share trailers... so this summer I've corrected 2 trucks and 3 trailers to get them all back to the standard....

Good luck on making it work...

One last thing that's been important to me... I ran a 8 gauge wire from the Battery to the 12vdc terminal at the plug, and than I changed the 12vdc in the trailer to same gauge wire... including the ground... I first noticed how much brighter my lights were on the trailer with a better ground.... and now traveling during the day I get my 5er batteries fully charged.....

 

[GrantP]

Just wanted to give a belated thanks to those who responded. I moved the center pin on the trailer wiring over to pin 4 and left the existing pin 4 wire there (now two wires coming off pin 4). Backup lights no longer come on and the battery was fully charged for the elk hunt. Thanks all!