Here is one to watch for, opened my engine hatch on the '78
while doing some stuff,  suddenly smoke, FIRE, from around the main
battery.  Didn't wait to investigate, ran around to sliding door,
ripped the extinguisher off the seat, and dumped a pound or so
of dry chemical all over that side of the engine compartment.  Well
ends up I overeacted as the problem had already solved itself.  The
hot wire over to the relay for the second battery runs in a black
sheath with the relay control wire on the '78.  Well on mine, this
bundle which runs up the side of the compartment, across the top by 
the fuel tank vent lines and down the other side to the relay, is
not cable tied down as it goes down to the main battery.  Runs right
beside some f.i. wires that are tied down then runs in their their clips
over the top but on the side near the hinge/prop it is not held down.
It had worked under the hinge/prop and when I opened the lid, straight
grounding of the hot 12 gauge wire from the battery which proceeded to
glow red hot, ignite its insulation then fuse itself in two.  Now my hot
battery connector had been replaced so maybe origionally it was fused at
the battery but I doubt it.  After reinstalling a new piece of wire,
Icable tied everything down solid then put a crimp in ATC style fuse
holder with 20 amp fuse right at the battery end, a wise idea when
installing anything like amps, lights, etc that you run directly
off the battery.  Anyway I advise anyone with dual batteries to check
out the situation and take whatever measures they deem wise.  BTW
cleaning up a dry chemical extinguisher from all over a Type 4 powered
Bus engine compartment isn't fun.  Thank the environmental freaks we
can't buy halon reasonably anymore.

John
ja@coe.wvu.edu