If you suspect the bulb, swap it with another bulb and see if the problem follows the bulb or not.

I can try to locate those relays on mine later (the labels seem to be in excellent condition). I'll post a pic if I find them.

I also get a fair amount of hum from some of the "hold relays" like the star bonuses. I think that is pretty benign, but if you want to look at that, there are some tips here: http://www.pinrepair.com/em/index3.htm#buzz

OK, that confused me. Each target (A,B, C, D) has its own reset solenoid. The wiring diagram doesn't show it correctly. For A&B path, the wire runs from the switch to the B solenoid and there is a second wire on the same lug that runs to the A solenoid. They are wired in parallel. Likewise the other path is wired from switch to D to C with coils in parallel.

The first image shows B target. There are two black wires attached to one lug of the solenoid. The other lug has two wires: BLU-R (blue with red tracer) that seems to match the wire coming off the switch on "long dwell", and what I can only guess was once grey with yellow tracer (not shown on schematic).

The second image shows A target. Because it's mounted with the bracket towards the front left corner of the playfield, I can only take a photo from an odd angle. That's the best I could get. One lug of the solenoid has two black wires (common), and the other lug has one wire that looks to be the same as the presumably grey with yellow tracer that came off of B.

I didn't take photos of C&D, but you can see the same pattern there. In that case the wire from the switch is GREY-W (grey with white tracer), but the wire from C to D seem to be the same grey with yellow tracer. (Maybe they picked the same wire to interconnect both pairs since it was not specified on the schematic?)

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