Travel Trailer batteries won't charged when hooked to my 2006 GMC

I'm having a problem getting my battery to charge up when it's hooked to my truck. When I went to raise the trailer uysing the electric jack after having been plugged into 120v all winter, it was dead. I had to plug the 120v back in to raise the tongue. This past week, before we went camping, I charged up the 12v battery (a cheap car battery because that's all I had at my disposal). We drove for 6 hours and the battery was fine for about 3 days. I decided to charge up the battery by hooking the trailer up to my truck. My brother-in-law brought over his battery/load tester and told me that there was no charge getting to the battery (it was at 10.5V and not moving). He thinks it's my truck (new to me 2006 GMC 2500 Duramax crew cab) because in his 2010 Ford F150 he had to install a fuse and a relay (that were in his glove box) to get his battery to charge. Do we have to do that for our GMs before we tow (and charge)? I think that it may be my trailer. Does anybody know what colour are the wires that lead from the 7 pin connector to the converter/charger in a 1986 Airstream 29' Sovereign - rear bedroom? I wouldn't be surprised if one of he previous owners disconnected the converter of the trailer from the 7 pin connector lead. Sorry for being so long winded.

Thanks,

Rod

Forget color. Electricity is color blind. Get a tester and start checking where you have 12 volts and track it all the way through. If you dont have a tester, make one with a spare bulb and some wire and tape.

Here is a link to a diagram for your 7 pin connector.

http://www.xplorethis.com/content/ba...n-plug-diagram

Some clarification of terms will help us help you. Plugged into 120VAC, your trailer batteries should be charged by the "converter" in the trailer.

The type of converter used in the '80s typically was a "dual-output", so named because it had one section to power the trailer's 12VDC circuits (lighting, furnace ignitor/blower, water pump, etc.) and a second to charge the battery when connected to 120VAC. When 120VAC was disconnected, a relay switched the house 12VDC circuits to the battery.

Contemporary converters are "single-output", where the converter is connected only to the battery, and keeps it charged when connected to 120VAC. The battery powers all 12VDC circuits whether or not 120VAC is connected. You can replace your converter with a single-output (recommended, as new ones have features that allow continual connection to 120VAC, and can actually maintain the battery including desulfating cycles - and your OEM is ready for an Antique Tag), but you may have to jump the old charger output connections to the battery to the single output of the new converter.

Anyway, your suspicions that the prior owner disconnected the converter charger section from the battery are well-founded - because you mentioned the battery worked for 3 days after you charged it with an external charger. The battery appears to be good, but it seems the converter's charge section is kaput - or it's been disconnected.

Some trailers used a manual switch to connect the tow vehicle's power to the batteries (but this is unlikely in your case) so the tow vehicle wouldn't drain the trailer house battery and vice-versa.

3 day's usable power from a single trailer battery is actually pretty good. (I have 2 6VDC golf cart batteries in series, and I can run the TV, satellite, laptop, and lights for about a day, which is a pretty heavy load).

Concerning the fact that the tow truck wouldn't charge the battery: The suspect connection would be pin 4, the 12VDC connector; if the lights, etc., work, the ground can be ruled out.

Anyway, I'd suggest you have two issues:

1. The converter's charging section is disconnected or not working (it may just be the cutover relay has failed- meaning it's not switching converter output to the batteries when plugged in).

2. The 12VDC (pin 4) is not receiving power from the towing truck, or if it is, the connection to the trailer battery has failed.

It could be that the 40 amp fuse in the drivers side fuse box under the hood was never put in or is blown. I think there are some earlier post on that. i don't think my 06 and 07 had them in when I bought them new. Worth a look.