Split charge relay question
 

On my van I have one of these, very basic, live and negative input from vehicle battery, and live output from other side, to aux battery, which powers a 12 v water pump.The earth on aux battery is connected to body. I have had trouble with van battery going flat a couple of times over last few days, went to local auto electrician, who tested the battery and charging system, and could find no fault, battery holding charge, as it should considering its only about 7 weeks old, alternator working as it should, and no discharge on the system. He suggested relay at fault, and to disconnect it when not using the van,I did this when I parked the van up at 4.30, just the positive side, when I came to move it on to the drive about 9.30, it wouldn't crank, jump started it from aux battery, started straight away. When I put a meter on the cable from the relay, with engine switched off, it was reading 12.83 v,. Am I right in thinking, that there should be no voltage at all with the engine switched off?Also how can the battery go flat if the live feed from relay was disconnected? can the earth still drain it?

Bump.........

You are correct. I assume you have disconnected the feed from the relay to the second battery. You need to disconnect the relay coil and the feed from the primary battery.

Disconnected the feed from relay to second battery, but relay doesnt have a coil,still connected to primary, but not connected to anything else.

Having got the main battery charged I would disconnect all the connections to the split charge relay ( and isolate all the wires) and see if the main battery goes flat, if it still does you have a fault in the main system , if it doesn't, change the split charge relay . I presume from what you have posted the system was working OK in the past.

Yes, had the charging system and battery tested by an auto electrician, and all was fine, no faults on system, or drain. so the only culprit can be the relay, which was disconnected last night, when I went to start van this morning, relay was still connected to the input, and it was warm, so its obviously not switching off. It has now been removed and a new one ordered.

update
 

So, new relay purchased and fitted, but there is still a 12 v supply coming from the output feed when engine is off? is this normal?

The relay should have a feed to the coil that is only live when the engine is running, the relay then switches, only then connecting the second battery into the circuit.

Well this is 12v perm live Ray. Its wired+ and- from van battery on one side and + to aux battery other side, with the aux battery earthed to the body.

https://m.ebay.co.uk/itm/Self-Switch...MAAOSw4QVZu-fh
This is what I am using