Brian,
I seem to be making some progress. I installed a long jumper from t-stat terminal 4 to control unit terminal 11, and this allowed me to start the heater. Now it's time to actually troubleshoot.
Jumping terminal 4 to 6 gives one long blink and 3 short, indicating "safety time exceeded no start". (Actually, this happened once, and now I seem to have entered some sort of ventilation only mode, where the blower comes on, but nothing else tries to start. Is there anything I could have done to stop if from trying to heat?)
I also checked the following:
Glow plug (resistance OK, relay clicking as normal, tried to start with glow plug outside of unit and got a nice red glow).
Resistance on flame sensor (just under 1100 ohms -- ok per your note above).
Visual check of PC board -- surprisingly clean for age, with all solder connections looking really good.
Disconnected exhaust for inspection -- no soot buildup whatsoever.
Disconnected air inlet, visual check of air outlet -- both clean.
Disconnected and cleaned terminals at fuel metering pump (see below).
No way of checking thermo-safety cutoff switch, but I don't think this is the problem.
Now, when I turn the heater on, the fan blows and the glow plug relay clicks (again, this happened a couple times, but now it just blows cold air and doesn't try to light the glow plug). During the times it tried to start heating, I had a voltmeter connected to the fuel metering pump, and after about a minute, I got 1-2 volts to the pump, but the pump did not turn on (no clicking) and no fuel moved through the clear fuel line. This makes me think the fuel metering pump is the issue (though I'm not sure why it's only 1-2 volts).
After a few minutes, the voltage went away and the heater shut down.
Do you concur that the metering pump is the culprit? Are there any other checks to make sure of this (can I supply 12 volts direct to pump and see if it turns on?) Where is my best place to source a new pump? Is this something I can purchase direct from you? Is the pump model specific or can I purchase one off ebay (here, for example:
http://www.ebay.com/itm/Espar-Fuel-...her_Vehicle_Parts&hash=item461980234c&vxp=mtr)
Thanks for your help,
Tripp