Old Carrier furnace: spark igniter

Re: Old Carrier furnace: spark igniter
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'
*** Puddin\' Man PuddingDotMan at GmailDotCom ***
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