Old Carrier furnace: spark igniter

Greetings,

I gotta Carrier upflow furnace (58GS075-2), made in '83.

It's old, but everything works except something in the spark
igniter circuit. I'm having trouble figgering what. I
replaced the gas valve 10 years ago, the rest is original
equipment.

Spark igniter (BDP model 733B) has 3 lo-voltage wires
(white, yellow, red) connected. Electrode (looks like
Penn model j996) has 120 v. wire (red) attached. Other
end of red wire is hard-wired into black 2 x 3 x 1 "
box labeled 'spark ignition'.

Tstat calls for heat. Vent damper does it's thing.
Pilot gas flows, and the igniter is supposed to
spark, but I can't measure any voltage from the
electrode to the pilot shield (or to the gas pipe).

I once lit the pilot with a match. It went thru the
cycle OK: fired the main burners, blower, etc.

I can't even get the lo-voltage connector to the
igniter to separate. Some parts of this furnace
look like they were engineered in Outer-Space.
Of course, I'm not a "Pro" ...

The igniter electrode *looks* OK. The wiring diagram
looks incomplete: I can't find the 120 v. to the
spark ignition box.

How to test the spark ignition (black) box? The
spark igniter circuit(s)?

Any/all help/advice much appreciated.

Cheers,
Puddin'
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