AuxiliaryBattery

[James Hewett]

When I picked up the Truck at the dealer there was a cord on the backseat, I knew it is the one I to use for the electric brake control. But what is the 40 amp.fuse that was taped on to it for?
Am I suppose to use it? Is that the one for the Auxiliary battery in the trailer?
When I checked to see if the battery was charging in the camper after hook up and a breif ride, I find it at only 11.6 amps in the 12volt outlet, and with the engine running in the GMC, it should have shown charging 13.8 amps.

[DmaxMaverick]

You are correct. The fuse is for trailer battery charging. Install it into the underhood fuse panel after you get your trailer wiring all correct. On your connector, if wired correctly, the "hot" wire is the top left, or about 1 o'clock. (connector on trailer would be 11 o'clock). You should have engine battery voltage there.

If you need a diagram of the recepticle click here (http://community.webshots.com/user/dmaxmaverick) and select Trailer Wiring.

CAUTION....
The circuit is always on once you install the fuse. It is not switched, or relayed. If you leave the trailer connected with engine off, it WILL discharge the truck's batteries if allowed.

[ropinfool]

You don't specify your truck but I will assume(and I hate to make an ass out of u and me ) that you have a new one. The fuse is for the aux power. Should plug into the power distribution box under the hood on the drivers side. John

[MTTwister]

You might want to think about a battery isolator for piece of mind. Heavy diodes, allows one way charging, but prevents bad battery sucking the life out of the good ones. Seen them at Checker Auto, etc, or an RV place could charge you a little more for it.

[Wing'n'it]

While battery isolators provide insurance against running down the truck starting batteries, they do come with a cost. There is a voltage drop of between .5 and 1.0 volts across the isolator. Combined with OEM (small) charge wires and long runs to the battery you will probably find just a trickle charge into the trailer batteries.

You can overcome some of this by replacing the factory charge wire with a larger gage charge wire, and reducing, as much as possible, the length of wire run.

IMHO, just unplugging the trailer from the truck when stopped overnight works just fine. Isolators are required in Class A, B & C motorhomes where there is no easy way to disconnet batteries and the wire wire runs are short.

Good Luck!

[James Hewett]

Dmaxmaverick, thank you for the detail picture! and thanks to all! I'm sure I have it all good to that point, trailer brakes and all other lights are fine too.
In that detail picture it shows charge batt. at 1 o'clock and Aux. in the middle, I beleive that is for either backup lights on trailer or a high mounted stop, either one weren't hooked there.
Now to get back to fuse point on underhood fuse box, every circuit seems to have a fuse, except top left corner(11 o'clk.) that has a red plug in it, it says in the book don't use it! Where else can the fuse go into?
Yes, I have a new GMC, it's my first non Ford and We Love it!!!

[James Hewett]

Wing'n'it, what can I do to run a heavier wire to the plug? Tap into the joining box for the dual batteries with a heavier and fused wire and run it into my 7 wire plug at 1 o'clock and cut off the red wire that is already there?
Will 12 gauge be right?
This is where my confusion comes on page 5-131 of the manual "It says } STUD#1 Aux.Pwr.(single battery and diesels Only)/ duel Battery(TP2) Do Not install fuse" What does this TP2 mean? or for that matter, what does the whole block mean?

[WanaDmxsub]

I tried to find the post that help me when I had this ? but was unable too. GM has managed to confuse the h@ll out of a lot of us with the wording about this fuse. What it boils down to is this, if you have a Diesel and want to use the truck to charge your trailer battery you will have to put in the fuse. Be forewarned that if you leave the trailer plugged into the truck when its not running you could drain the truck batteries.

[James Hewett]

Well! I guess it's OK with the fuse in now , I used the test light and I do have 12volts at the 1 o'clock contact, haven't got to hookup to trailer again, but I guess it won't be any different then past yrs.
I usually unplug when we get to a campsite, even on the occasional boondock'n, Trackside we are prepared to run generator like all around us.
At least now pulling the trailer down the road with this GMC, I'll have more faith in make'n the trip both ways.
I'm going to keep my eyes open for an isolator. smile.gif

[Wing'n'it]

James,
Sorry for the delay in responding, but I'd attach the new power lead to the jump start power block (don't know the technical name) under the red cover left side of center in the engine compartment. I'd use at least a #10 multi-strand wire, #8 would be better. You can probably get the wire at a marine supply store. Remove the existing charge wire from the truck side of the trailer plug and replace with the new wire as you suggested. When running the wire to your plug, be sure to protect it from rubbing or being pinched. Also, for fire (short) protection, you should put an in-line fuse to protect the line from a shorting problem. A 30 Amp fuse is more than enough, 20A would work also.

As an additional thought, have you considered a solar panel on the roof of your trailer? I have two 100 watt panels on top of my 5th wheel and they work great. First they keep the trailer batteries always charged up while in outside storage, and second they reduce the load on the truck electrical system in recharging the trailer batteries. In full sun, driving down the road, the panels provide 12+A @ 14.0 VDC at the batteries, much better than the alternator can provide.

Good Luck!

Mike

[rjwest]

If you increase Charge wire size, you will also need to increase ground wire to same size.

A battery Isolator " Relay " is best . Least Resistence, available at RV stores.

It is powered by Ign switched power so camper is connected to truck only when Ign on. ( I have a truck camper, so it easy to forgot to Plug'or unplug. If you " rest stop camp " isolator relay
may be a good idea for trailor also.