Frank Condelli mentions:

I think I've finally gotten this thing sorted out, with the help of a few
of you, especially Derck.     The   relay is an ordinary relay and must be
good for at least 30 amps as it must switch the fridge power.  

Actually, on my 89 the relay isn't just an ordinary relay.  If you look care
fully at the top of my relay's case, you'll see the schematic for a diode 
in the activating coil circuit.  You can check your relay with an ohmmeter.
If the diode is there the resistance one way will be greater by far than 
the resistance with the leads switched ( the ohmmmeter leads ).

What this diode does:  The activation coil allows the relay to be closed
when the alternator voltage exceeds the battery voltage.  You can cleverly 
rewire this relay to work in a dual battery setup where the alternator is
charges both batteries when the relay is on but isolates the second battery
when the alternator is off (blue wire).  Now you can suitably fuse the lead
from the second battery with say 40A or so to the refrigerator/isolated power
circuit so you can run the fridge on DC with the motor off.  

To run other accessories such as the interior light and radio you'll have to 
run an additional power lead to the relay panel under the dash and isolate
the radio and rear light circuit and connect them to this new auxilliary 
battery lead.

I don't remember the supplier for Derek's high current relays bu these would
be handy for a more sophisticated isolation system.

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