After looking at my van and doing some research I have some questions about the dual batteries. This is a 96 7.3l van by the way.

Can you connect the GPR up to either battery? My GPR is right next to the driver battery but is connected to the passenger battery with like 3 feet of heavy gauge wire?
Why does the alternator connect to the passenger battery?
Does it matter for anything which battery you connect it to?
Why are the batteries not the same size/capacity? Just for space?

 

both batteries are in parallel

i agree with shorter cable but wasnt designed by me

trucks are wired to pass battery and drivers is the second one

the truck use same batteries on both sides not sure on a van but space could be an issue.

Make sure both are new or the good one will charge the bad one and both be dead in a few weeks.

 

thanks for the reply knottyrope

"trucks are wired to pass battery and drivers is the second one"
So any harm in attaching loads to the drivers side battery?

"the truck use same batteries on both sides not sure on a van but space could be an issue."
Definitely different batteries on the van, the smaller being on the passenger side.

"Make sure both are new or the good one will charge the bad one and both be dead in a few weeks."
Yep both batteries pretty new, bought and installed same time.

 

You can re wire it to the drivers battery, it should not hurt any thing if you prevent the cable from chaffing anywhere.

take a pic of the area if you can. we like pics on here

 

Here you can see my GPR next to the driver side headlight bucket, inches from the driver side battery tray. It attaches to the passenger side battery with over 3 feet of cable. Not that there is anything wrong with long lengths of appropriately sized cable, but why not just run it to the driver side battery?

 

Just as a clarification, the solenoid pictured above next to the driver headlight is actually the starter solenoid.

But still I don't see when all loads and charging circuits need to be attached to only one battery. I would imagine Ford did so for a reason though. If anyone knows I would be super interested.

 

Why to one battery, simplify troubleshooting

 

The manufacturer does have some incentive to keep troubleshooting straightforward. Good point, thanks for your input.

 

What type of van is it? A bus conversion or RV? On my E350 bus, I had that solenoid relay like the one you show. It was hooked up to the "run" of the ignition switch to charge 2nd battery. Now after total rewire from the conversion company to bus(what a mess). I run dual alternators. The now original style alternator(it was a 200A Liece Neicevill?? sp)) charges the chassis battery and 2nd added alternator charges the coach battery. Only the chassis ground are common.

 

Short answer, even though parralelle connected.

One battery is the starter battery, the other is accessory.

It probably draws off the spare battery and starts off the main.

Even though that makes 0 sense, DC is weird.

The load is still there directed at the battery even with a shared powersystem.

 

from my understanding, running parallel keeps voltage the same but allows for double the cranking amps and reserve capacity. this would be why diesels have dual batteries over single
I forgot what the question was for the OP, so disregard what I said if it's not helpful