General Electrics question

[Lwh56]

I’m after some advice.
I own a Peugeot boxer van that was privately converted some time ago. I do not have any problems with the electrics but I intend to do a minor upgrade ( more about that later …) and would like to fully understand what was done, without the need for tracing every wire.
My idea:
At the leisure battery there will be a number of wires attached to the +ve terminal. I should be able to determine where each of them originate from by disconnecting it and doing some voltage measurements - for instance - if it only has 12v when the EHU is connected it most likely originates from the Sargent ec155,
Another example is if disconnected the 12v fridge doesn’t work… so on an so forth. The wire I am really interested in finding is the one that has well over 12v when the engine is on/revving. Because this is the wire that one way or another originates from the vehicle battery.
It would be this wire that I will use as input to a victron dc to dc towards charging a Lithium battery (when I eventually replace the lead acid one that the wires are currently connected to )
Is this a sound way to proceed? Labelling each wire and hopefully identifying the important one!
Thanks is advance
Les

 

[t0mb0]

Yes, that’s the general idea if they’re (annoyingly!) not labelled.

On your “number of wires attached to the +ve terminal” point though - they shouldn’t be directly connected, they should be going via a fusebox or possibly individually fused. You can then just pull the fuses one by one to verify where each one is connected to.

 

[Lwh56]

Thanks for that…might prefer to wait for warmer days though
What started me thinking about this was a puzzle. I had always assumed that somewhere between the vehicle battery and the leisure battery was the classic relay until Someone reminded me that the EC155 has this functionality built in, however what’s odd is that when on EHU only the leisure battery gets charged - the vehicle battery doesn’t. Not only that but the little control panel that shows the battery state and switches on the 12v system etc has a second battery indicator that is always dark. So that makes me think they didn’t bother wiring in that function. Anyway, I suppose it doesn’t matter what route it takes…
Thanks again.