Not much to it... drain the coolant (open up the block drains if you can -
it'll make less of a mess that way). Knock out a core plug of your choosing
(whichever is easiest to get to - and of course, one that's the same size as
the block heater - pretty sure only the ones on the back are larger).
Easiest way to remove them is to put a blunt punch (big, wide flat-blade
screwdriver works) on the edge of the plug and smack it with a hammer. The
plug should tilt out, and you can yank it out with pliers. If you didn't
get the block drains open, be prepared for more coolant to come pouring out.
Tap the new plug back in gently, making sure it's sitting even in the bore.
Now hook up the wires, and re-fill the coolant.
If that's one of the units installed in the lower block, you might run
into the problem I had on a 318 V-8 my son had in a 72 Dart . . . only
one side of the block got warm from the heater, and the other side was
as cold as the rest of the outdoors.
So you might need to run a pair on your V-8. . . .we just fixed the
choke and crossover passage (unplugged it) instead.
Probably a good idea... the factory block heater came only on one side. I
forget what the heaters are rated at - might want to check and make sure
they won't overload a typical 15A circuit. I don't remember what the gas
engine heater elements draw - but I've seen references to block heaters
drawing 7-8A (though this is probably the larger element used in the Cummins
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