For the 100pt relay to energise when red and yellow inserts are paired, the current has to pass through the wipers and rivets on the advance units - these are stepper units under the playfield, one for red and one for yellow.
Check for broken wires, bad connections between rivets and wipers, gummed up wipers.
The circuit in question is the green-yellow wire on the red unit, the yellow-red wire between the stepper units and the orange-green wire on the yellow unit.
"L" is the 100pt relay.
Hope this helps, Richard.
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