Quoted from hjh632:T and D (tilt and reset) units don't activate.
I'd start by sorting out why the D/Reset relay doesn't fire.
Square Head Reset relay (resized).jpg
To do that I'd unplug the game and break out your meter. Set the meter to the lowest resistance setting, clip one probe to the red-white wire on the right side and leave it there. Then work your way through the circuit to determine why current doesn't flow through the D/Reset relay coil. Start by clipping the 2nd probe to the red-yellow wire on the other side of the Zero Balls To Play switch which is probably mounted on the Ball Count unit. Find the position of the Ball Count unit that closes the switch and see if the resistance across the switch drops to an ohm or less. If the switch closes but the resistance doesn't drop the switch may need to be cleaned.
Once you get the resistance to drop to less than an ohm, leave the Ball Count Unit where it is and move the 2nd probe to the left, to the orange-white-red wire between the 1000s and 100s Score Reel Runoff switches. Now you're checking the circuit through two switches. Rotate the 1000s Score Reel so it shows something other than zero. The resistance should again drop to less than an ohm. If not, check that the 1000s Score Reel Runoff switch is clean and working properly.
Once you've verified that a portion of the circuit is good, move the 2nd probe further to the left to include another switch and repeat the process. Eventually you should get to the D/Reset relay solder lug with all the switches cleaned and working and the resistance should still be less than an ohm. At that point the relay should fire properly.
/Mark