87 westie.
12 v's are going going to the black line that connects to a junction
block on top of the fridge. it turns to a red wire that heads over to
the switch. from the switch it comes back to the block as a gray wire
that heads over to the heater and back as a blue wire to ground.

I did a resistance check from black to red then to gray and nothing is
going to ground. I've checked across the heater wires and its not going
to ground. If i volt meter the wires from the battery its 12 but when i
plug the fridge in, the volts drop (like the heater is sucking it up)
but heater doesn't get hot (I've pulled the insulation away from the
heater tubes.) It works fine on 120 volts.

This thing is driving me crazy. Can the heater be defective even though
its showing zero resistance and not going to ground internally?

Kind regards,
dan