Desa Reddy heater - no spark!

I have a forced-air Reddy heater model R100A (90,000 BTU) that isn't firing. Here's my troubleshooting steps so far:

1. Opened the cover and checked for spark by watching the spark plug directly - no spark seen.
2. Removed air hose and fuel line. Cleaned spark plug and checked gap before retesting for spark - no spark seen.
3. Removed spark plug and clamped it to side of burner before retesting to get a better view of it - no spark seen but got a shock when I accidentally touched the metal end of the spark plug wire.
4. Put a regular automobile spark plug light between the cable and plug. Reinserted plug and tested again - no lights from spark plug light.
5. Replaced spark plug with new plug and retested - no spark seen.
6. Held spark plug cable end close to the heater chassis and tested - saw spark only when held very close to chassis (virtually against the metal.)
7. Put spark plug light on end of spark plug cable and held the end of the spark plug light's cable near the chassis - no spark seen.
8. Pulled the spark plug cable leading from the ignitor switch out from the holes in the chassis to avoid any potential arcing from the cable - no change in results.
9. Made sure ignitor switch is well grounded and retested - no change.

So at this point what could be the cause? Is the photo cell possibly involved in the problem and how can I test that? Or am I looking at a bad $110 ignitor switch?

 

I sure don't know much about these things, however, I would think your igniter is bad or if there is a separate capacitor, I'd replace it. If the photocell was tied into it and bad, then I would expect it to ground the spark totally, and you would not get shocked or see any kind of spark at all.