Strange electrical issues when switching from truck batteries to dedicated deep cycle

[Mcstiggens]

So here's what I'm dealing with.

I gots me a '98 Four Wheel hawk camper.
I installed two 6v golf cart batteries (costco brand) wired in series. This is supposed to be the best arrangement with regards to max amperage.
This setup is not wired into the truck charging system yet, It is a completely separate system. So when I am driving down the road, I have the camper plugged into an outlet in the truck bed that runs off the truck. That way I can keep my fridge cooling off of 12v while traveling.
When I reach me destination, the idea is to unplug the camper from the truck's system and plug it into the 6v/series/12v battery bank for dry camping.
This is where it gets weird:
All of the electrical works fine when plugged into the truck battery ('95 Ford F250 7.3L diesel with two starting batteries).
BUT when I plug the camper into my battery bank:

The good: My exterior 'porch' light works fine, my fridge seems to work fine, my furnace fan works fine.

The bad (weird): The two interior fluorescent lights don't work, the furnace igniter doesn't work.

Any ideas as to why this would be the case? I was thinking it might be an amperage issue (i tried testing it but so crappy was my Harbor Freight multimeter, it died before I could get any results. New one on the way.....this time not from HF!)
From my research, the two 6v GC batteries in series will yield more amps than grp 27 12v batteries wired in parallel so I can't imagine amps are the problem. Besides, should I not be able to run ALL of my meager requirements on a couple of deep cycle batteries?

Thanks for your input,
Mcstiggs

 

[Martyn]

Sounds like you have bad grounds on the circuits that don't work.

When the camper is plugged into the vehicle the vehicle is providing the ground for the electrical system. When you are running off the in house batteries the camper is providing the ground.

Shouldn't be too hard to test the theory out using a multimeter.

 

[Mcstiggens]

Sounds reasonable but would not the furnace fan and igniter share the same ground?

Thanks,
Mcstiggs

 

[Tony LEE]

How are you charging up the house batteries before you leave. Are you sure they are fully charged.

I know that some RV HWS and furnaces are a bit fussy about the ignitors getting the full 12.5+ volts or they are erratic in operation. Same with some inverter circuits in fluoro lights.

 

[Mcstiggens]

How are you charging up the house batteries before you leave. Are you sure they are fully charged.

I know that some RV HWS and furnaces are a bit fussy about the ignitors getting the full 12.5+ volts or they are erratic in operation. Same with some inverter circuits in fluoro lights.

I had them on a trickle charge for a couple days and they are brand new, first time out. They tested @ about 12.9v.

 

[brian90744]

battery problem

Try hooking the battery charger to the house batteries, and test the items with problems. Could be just low batteries?? If the items work on house current110V they should work the same on 12V(battery)
Pre-cool your 12V refrig.
just FYI=brian

 

[Martyn]

Sounds reasonable but would not the furnace fan and igniter share the same ground?

Thanks,
Mcstiggs

It's going to be difficult to pin point what is going on if you don't have a wiring diagram or a good understanding of the wiring. Could well be everything has it's own ground, which personally I think is the way to go.

I always look at grounds first if there is something strange going on with DC electrics.

 

[brian90744]

So what solved your problem????
brian

I had them on a trickle charge for a couple days and they are brand new, first time out. They tested @ about 12.9v.

 

[Mcstiggens]

The problem is yet to be solved. No time yet to trouble shoot potential ground issues which sound like the place to start.

Stiggs

So what solved your problem????
brian

 

[Gooseberry]

Just ground the deepcycle to the frame and I bet it will fix your problem.

 

[oldnslow]

Check the polarity of your new batteries and wiring. Light bulbs and fans will work on either polarity (the fan runs backwards) but fluorescent lights and the furnace ignitor won't.