Switch panel made and installed:
Panel in action. The hard click when the switched is turned on and off is the solenoid closing and releasing.
So the next problem was: the van's rear heater is either On or Off without a thermostat to control the On/Off cycle. So after the engine has reached its operating temps, it can get uncomfortably warm in the back. So I bought this $8 12v thermostat kit:
http://www.electronix.com/catalog/product_info.php/cPath/8_45/products_id/10962
I flipped some of the parts to the underside of the PCB so it would be easier to install onto the van's control panel.
Top side of the PCB:
Bottom side (during testing):
I made a bracket to hold the PCB to the van's control panel but forgot to take a pic. But here is the front side with a blue knob installed to control the desired ambient temp:
Since the thermostat is supposed to control the back of the van, then naturally the sensor (a thermistor) had to go to the back. So I whipped up a housing for the thermistor from some plastic I found in the basement, a blank RadioShack proto PCB cut to shape, a RadioShack
PC board terminal, and some high density polyurethane foam (looks like wood) to hold it all together. I salvaged a Molex 8981 connector from an old computer power supply and used it to separate the thermistor assembly from the (very long) wires which run up to the front control panel.
Pulled out from the housing:
And then it was time to pull down the corner panel from the van, epoxy down the thermistor housing to the back of the panel, and run the wires up to the front control panel. After the epoxy dried, a hole was cut into the fiberglass corner panel to allow ambient air to flow into the thermistor's housing.
Testing vid. The knob was first turned up to increase the desired ambient temp, which then closed the Heater circuit (as indicated by the LED turning on). A heat gun was used to blow warm air into the thermistor assembly's hole/housing and the thermostat circuit disengaged the Heater circuit (as indicated by the LED turning off).