the B relay needs to power. Quick check is when you've stepped up the balls played unit enough times, manually close the B relay (push the armature plate onto the coil top). If XB trips, your problem is getting B to power.

if XB doesn't trip, it may be easier to use a voltmeter.

if you manually close or jumper closed the B relay switch when the balls played unit is stepped up enough, the circuit should be complete from the RED-WH wire on the 10A fuse to the XB relay coil (BL-BLK wire).

one probe on the black wire on any handy 25V coil and other probe anywhere in the XB circuit should show 25VAC. If it drops a lot, you've found the cruddy switch/wiper.

pedantically, the 25V wire on the transformer is red-yellow. Welcome to wire fade

the red-yellow on the transformer becomes red-white on the other side of the 10A fuse.

keep in mind that there are multiple red-white wires in the game. They are not all the same wire, so you need to be careful which one you are attaching to.

often the "power rail" wire is lower gauge (fatter), but not always. It's best to attach your jumper to a spot you know is the wire you want per the schematic. The 10A 25V fuse is guaranteed correct and you can clip on to either side assuming the fuse is good (if it isn't, nothing but a few lights would work).

wrt the relay bank, assuming it's the kind with a couple big wing nut-like screws on the ends you can loosen those and flip the thing up to access the pieces. Make sure you seat the bracket notches all the way onto the screw shafts or the relays may have issues tripping or resetting.

per what mark said earlier, trip relay coils are either driven from a pulse (score motor switch) or there's a switch on the relay itself that disconnects the coil as soon as the relay trips.

if you jumper power to a coil, you may get some buzzing because you are typically holding the coil powered longer than the game would. It's mostly wear on the armature plate and coil top that causes the buzz, and it's not a problem ... except when it's the 30 or 115V hold relays or coin lockout coils and the buzzing is annoyingly loud.

if you power the coil of an already tripped relay, buzz may be all you'll notice.

per the schem, XB does not disconnect itself. All you really care about is verifying XB trips when powered ... you're just proving the coil and mechanicals work.

you can manually reset a trip relay by raising the lifter until it latches up.

if you run into a situation where XB always trips when using a jumper directly to the coil, but doesn't reliably trip in game play, then you need to figure out which switch/wiper is causing the problem. A good first guess is the switch creating the pulse ... in this case it's not that easy to figure out since gtb wasn't nice enough to put the timing diagram on the schematic. See https://www.funwithpinball.com/learn/animated-score-motor-circuits for an example which may not be the same as Mayfair.

however, you do know that when the score motor is not running and the balls played unit is at step 4 and 5 (3 ball game) or step 8 and 9 (5 ball game), the only open switch in the XB relay circuit is the B switch ... and you can manually push down the B relay armature to close the switch any time you want.

'course, be aware of side effects. If QB trips, then the XB circuit is disconnected. If the balls played unit steps, make sure it's still on a step closing the circuit.

you can also use a jumper to not care about some of the side effects.

for example, if you do the below then XB should trip if you manually push down the B relay armature regardless of anything else. Manually reset XB and operate B a few times. The key thing is try and operate B the way the game does it ... push the armature down squarely onto the coil top. Don't tilt/rock the armature or push down too hard ... that can make a flaky switch work when it normally wouldn't.

if closing the B relay with the jumper in place works every time, the B relay and motor 1C switch is ok and the issue is probably balls played unit wipers or the PB switch. PB is bypassed at step 5 or 9 of the unit, and QB/SB switches are feeding other circuits ... so what is happening with those narrows down where the issue could be.
mayfair jumper test (resized).jpg

don't worry about QB until you get XB tripping reliably.

XB needs to be tripped, B needs to be powered and score motor 4C has to create a pulse to trip QB. If you are manually tripping XB or using a jumper, the score motor may not be running and/or making pulses at the right time or B state may be wrong. Whenever you are manually changing the game components, it's possible to get the game into an impossible state and things after what you did won't work right.

reset will clean things up unless it's something rare like the tar pit on a 4 million BC where the state is inconsistent if you manually move a ball in/out of the pit.

if stuff just doesn't make sense, the almost never fail approach is disconnect the score motor. Your game is probably too old to have the "service jack" where you could just unplug it, so you have to unsolder a motor wire or stick paper in multiple switch contacts. Jumper the motor so it works and get the game into a state right before you want to see what's going on, then disconnect the motor.

trigger your event ... drain ball, manually close B relay, etc. ... then turn the score motor cams by hand to see what happens as the switches you care about close. You can stop turning at almost any time and see what various units are doing, take meter measurements, or poke/wiggle/whack stuff.

the one gotcha to turning the cams by hand is be careful not to leave solenoids (coils with plungers) powered a long time. Most solenoids will survive 30+ seconds and even letting a little smoke out, but don't leave the 120V ones like the control bank reset powered or the fuse will blow.

it's probably best if you are doing something that will cause the 120V solenoids to power to remove the fuses to them as even turning to cams too slowly will blow those fuses IF the circuit becomes active (normally just when debugging a reset sequence issue).