So I get about 2 hours sleep last night. I get back up and start on
the heater. There was some coolant inside the cap that covers the
bottom of the Rusco heater. But it was enough work that I didn’t want
to put the heater box and all of those hose and electrical connections
back yet again to see if a little coolant caused the ground fault.

So I machined shorter the mounting lugs on the one end of the Hotstart so it
would fit in the heater box. The Hotstart required that the water pump
be moved down a couple of inches and angled slightly to line it up
with the opening. That also required the Hotstart to angled as well. A
90 degree bracket had to be fabbed to mount the Hotstart. All of this
required a few holes to be drilled. I finally got very tired at 6am
after working 4 hours, and had to stop. The only thing left is to
crimp the power leads and temp sensor leads to their respective
crimps. It all looks like it will fit nicely. Hopefully this cures the
ground fault issue. I usually hate to guess, but this was pretty
clear, not absolutely certain, that it was a ground fault.

I’m also putting a pair of connectors in line with the high voltage
leads and another one for the temperature sensor. It would even be
useful to put a connector in for the pump since it would make adding
power to the pump during the rather long priming operation, much
easier. It would make it nicer to diagnose an open heater element if
all I had to pull apart a connector and buzz it out. The military
style connectors are a pain to remove to check these very items. So
the connectors make it much easier in the future.

I found out from the original owner that the truck’s AC and heater
have never worked. The AC will be an interesting debug for sure if
this fixes the heater.

Heater Specs: 240vac, 1500w, Brand: Kim Hotstart, Spokane WA, P/N: TPS152GT12-000, On 120F(49C), Off 140F(60C).