Wiring battery combiner into 7 pin harness

[fr500c]

Hey everyone. I've got my truck camper permanently on my 1998 GMC K3500 and unfortunately cannot easily access the 7pin harness to unplug when it is off the truck. I quickly realized that with it fully plugged in that the 12v charging cable from my 7pin harness will drain the truck batteries.

I have ordered a battery combiner and am looking for where to wire this in.***Link Removed***

Can I just splice this between the 12v wire going into the 7pin trailer plug? I can easily access that under the bed of the truck.

Is it that simple or am I missing something? Appreciate any help!

[2112]

Gdetrailer wrote:
Instead, opt for a $8 12V relay which the coil is connected to the ignition keyed source which is powered only when engine is running.

Common 12V relays are the "Bosch" cube style which are typically 30/40A which would be enough to cover the charge fuse.



For overkill they do make a 70A Bosch style relay..

I agree with this

I used a few similar to These Cheap Chinese 80A Relays because they came with a Bosch compatible socket, thinking I would replace them with the Bosch 70A when they fail. 4 years later one is switching 120VAC ~12.5A and the other switches ~8.3A a few times a day Without issue using a 12VDC controller.

You can use a fuse tap to access an accessory control voltage.

[opnspaces]

Aux A or Aux B were the two charge posts on my 1996 Suburban. I'll bet you you have wire on one of the two.

[BurbMan]

There is no "stud 1" on a 1998, that was from 2000-2007.

Here is the underhood fuse box, I'm not sure which feeds the 7 pin trailer connector. My guess is either the "Aux A" or "Aux B" studs.

[BFL13]

fr500c wrote:

BFL13 wrote:
Just pull Stud 1 fuse under hood

https://www.google.com/amp/s/www.autogenius.info/gmc-sierra-mk1-1996-1998-fuse-box-diagram/amp/


I can’t seem to locate stud 1. Feeling like a real idiot at the moment!

WARNING That link is infected if you hit Continue!!!! had to restart.

Anyway there are no idiot Chev owners 🙂

I have a 2003 so the 98 is not the same it seems. I have a gas with one battery and the trailer package. Diesels with two batts are different also AFAIK.

In the 2003, the 7-pin 12v is from a 40a fuse in the under-hood fuse panel and it has a red dummy fuse that is near it. Sorry don't know the 1998 version.

BTW if nobody here knows try the Tow Vehicles forum. Lots of truck guys on there who would know.

[fr500c]

BFL13 wrote:
Just pull Stud 1 fuse under hood

https://www.google.com/amp/s/www.autogenius.info/gmc-sierra-mk1-1996-1998-fuse-box-diagram/amp/


I can’t seem to locate stud 1. Feeling like a real idiot at the moment!

[enblethen]

This one is almost over kill! Battery switch
Connect 12 volt charge wire from power center. Connect control conductor from a "hot" in run.

[Gdetrailer]

BurbMan wrote:
You do want some type of battery isolator like this one so that when the truck is running you'll charge the camper battery. Pulling the stud 1 fuse will prevent the camper from draining the truck battery but will also prevent the truck battery frm charging the camper battery.

The isolator can be anywhere between the two batteries, either under the hood, under the the bed or in the camper. My 2002 Lance had one under the sink where the 7-pin cord came inside.

Isolator, expensive overkill plus the isolator will have at least .7V voltage drop which pretty much effectively kills your charging potential to the TC battery when engine is running.

Instead, opt for a $8 12V relay which the coil is connected to the ignition keyed source which is powered only when engine is running.

Common 12V relays are the "Bosch" cube style which are typically 30/40A which would be enough to cover the charge fuse.



For overkill they do make a 70A Bosch style relay..

[BurbMan]

You do want some type of battery isolator like this one so that when the truck is running you'll charge the camper battery. Pulling the stud 1 fuse will prevent the camper from draining the truck battery but will also prevent the truck battery frm charging the camper battery.

The isolator can be anywhere between the two batteries, either under the hood, under the the bed or in the camper. My 2002 Lance had one under the sink where the 7-pin cord came inside.

[Grit_dog]

Yeah that works. Pulling the right fuse. Although a battery combiner (voltage sensing relay) would work too, automatically.
Idk which one you have as apparently it’s censored on here , lol , but the ones I’m familiar with are heavier duty than the little charge wire and current going to your trailer plug.
Have had a Blue Seas combiner in our boat for years. It’s great. Automatic charging when engine running and almost instant disconnect once engine is off.
What you are planning is literally hands off if you are frequently driving and want to take advantage of the bit of charging you get from the truck.
If you’re just doing it to keep from killing truck batteries and not relying on any charging while driving the easier thing is just keep the 12V wire or fuse disconnected from the camper.
There’s other options too like put an ignition triggered relay in line to the trailer plug. (Low tech version of the combiner.

[wnjj]

You can take the wire off the stud and install the isolator there. That way you don’t even need to open the hood, let alone pull the fuse.

[fr500c]

BFL13 wrote:
Just pull Stud 1 fuse under hood

Wow... I feel like an idiot. Haha. That is way easier. :S

[BFL13]

Just pull Stud 1 fuse under hood