24v electrical nightmare

[doka404]

Ok so when you disconnect the positive from the first (LHS looking from the front) battery, you still have the issues. I am assuming you don't have any Aux (third) battery connected up anywhere? Kinda got me stumped as well but going to throw some ideas out there..

The way they are wired up (guessing its the same as my Safari) is :

You draw power from the LHS Positive Battery
A long cable runs from the LHS negative across the front of the car (behind grill from memory) to the Positive of the RHS battery
The RHS Battery negative is then earthed to body etc

How much voltage do you have? Is it leaking 12v or 24v or??..From memory Oil pressure and water temp gauges are 12v (run from a little invertor in the back quarter panel) so may help point in the right direction.

By the look of it though you have something connected to the second battery (RHS) so using it for a 12v Source?

This may explain why you see two different voltages on the batteries. Although I would expect to see the RHS battery lower. If you keep drawing 12v off one battery you will find your battery life is effected and unfortunately with a 24v truck once one goes its a good idea to replace both as the old one will bring the new one down to its level. You can buy battery equalisers, but even they are not perfect.

My first check would be to see if there is any broken insulation on the cable that joins the two batteries (from LHS Neg to RHS Pos) that was shorting out. Even disconnecting the positive from the LHS battery would still leave 12v coming from the RHS battery. So what voltage is leaking? What happens when you pull both the LHS pos and RHS Neg off? Does the problem stay/go away? The fact that when you pull the pos from the first battery and still have stray current got me thinking along these lines. But then again you say you have checked and replaced all of the battery cables so kinda rules this one out..

Pull ANY after market wiring off the batteries leaving only the basic (standard) wiring to run the car.
If the problem goes away, add the extra wiring back one by one and see which one causes the problem.

As 3Dogs said..do things one by one..Its just going to be a matter of taking your time and taking things out of the equation.