johnr9q

On my Dodge Ram 2500 Diesel truck 7 pin trailer electrical connector there are actually 8 wires going in it from the back side. What is the extra wire for? Is this connector only intended for light duty use cause the wire that is used in the RV to charge the batteriec from the tow vehicle is only 14 awg. I've been running a 12.5 amp Frig as well as charging low batteries so probably pulling much more amps than I should.

thecatsfan

The extra wire is a second ground wire. I believe it is just to be redundant for safety.

The charge line in the seven pin connector comes from a relay in the PDC that limits the current draw to 40 amps. I thought my charge line was 12 AWG, but I'm not positive. With a peak output of 40 amps at 14 volts, you're never pushing more than 560 watts on that line. 12 or 14 AWG should be able to handle that.

Yeah, it does seem like a larger gauge wire would be a little better, but that's what they used.

johnr9q

Thecatsfan: Thanks for the info on the 8th wire. I found the items you are referring to that are 40 amp in the PDC. On the underside of the PDC cover it identifies these components as "40 amp trailer" and "trailer relay" One may be for the trailer brakes and the other for trailer charging circuit? When I pull out the one that says "40 amp trailer" I hear a solinoid click which makes me think this is only protecting wires to a solinoid. In all my experience a 14 awg wire should never be protected with a fuze larger than 15 amps. I called Dodge Tech info but they couldn't explain anything and suggested I go to the dealer. The dealer's electrical guy isn' t talking till friday and then who knows if he knows.

natstayl

Since the load is relay controlled, the hot wire doesn't have to be as heavy to support the load. However this also means the insulation can melt off the wire during a dead short to ground before heavier fuses shoot.
The additional wire is a second ground. On the 2003 both ground wires are connected to the same lug to the frame below the left taillight.
Nat

johnr9q

natstayl: Thanks for the info. So it sounds to me like Dodge was trying to save some money by running a 14 awg wire instead of the required 8 awg. But if I pull more than 20 amps thru that wire at times and the wire gets hot, sounds like I don't have a very efficient system so I guess the best thing for me to do is rewire directly from the battery of my Dodge with #10 wire and protect it with a 30 amp fuze. I think I'll also run a #10 wire as a ground also directly from the battery. I'll need to get another 7 pin connector for the rear of the Dodge as Dodge has a plug in to the rear of the connector that is permanent with #14 wire on the battery position

natstayl

Heavier guage wires are best but...
I wouldn't run a 10 guage to the 7 pin connector if it was me. I like instead what another DTR subscriber did when he installed + and - lugs at the back end of his truck with wires he said were the same guage as jumper cables. He has a pic in his gallery. Since I can't remember who it is, why don't you do a search about installing battery terminals at the rear of the truck or else open up another thread about installing + and - terminals at the back of the truck , if your search doesn't find anything.
Good Luck,
Nat