David,

As one person already wrote - If only your auxiliary battery is
draining, then search the circuits that are wired to it and nothing
else.   That should simplify the hunt for the bad circuit.

Seems that some are missing this and telling you to check all the
circuits up front - not necessary unless they are re-wired to the 2nd
battery.

You say that your battery drains down in a couple weeks' time.  That is
a very small draw - assuming that you aren't driving the van.  A major
drawing circuit will drain a battery overnight and even something
relatively moderate will do it in a couple of days.

Do you drive the van?  How much?  If you are driving it, it should be
charging back up and not draining down with what ever is this small draw.

If you are driving it regularly and ever couple of weeks you end up with
a dead 2nd battery (how do you become aware of this), then you likely
have an intermittent short, and this could be trickier to find because
it has to be in the "shorted" state when you are checking for you to
find it.

How were your two batteries originally connected?  Makes me wonder when
you say they were both draining.   Didn't you have a relay or something
to separate them before you put in the isolator?  In addition to the
items named in your first post, what other accessories are wired to the
2nd battery?   In your setup, how does the 2nd battery get charged?

If the voltmeter is a multimeter, then you can set it to DC amps and be
a bit more accurate than looking for sparks - though the sparks method
will work.  As was suggested, if the devices are off, the volts reading
would also be zero, so you also can use volts to check for an open
circuit.

Sam

--
Sam Walters

Baltimore, MD