Hi, I have an 83 Westy I'm  trying to hook an auxilliary battery up to, 

    This model has the small silver cube under the driver's seat in the auxilliary battery compartment. I guess this is some kind of relay or isolator. It has five wires connecterd to it. 

  4 of the connections are labelled 30, 85, 86 and 87 the fifth connection is unmarked.I just want to get my auxilliary battery hooked up so it gets charged while the van is running. I also want to be sure I can't accidentally drain juice from my primary battery .The only stuff I've found on this has been for late 80's vans , someone said the early 80's vans were wired differently.

 Can I simply ground my auxilliary battery and connect the +ve terminal to terminal 87 on the relay box?