I owned a Twinky that was the AAB version. It operated the same way that your Bronco appears to.

The Backglass was in rough shape, and was the replay glass with a decal affixed over the replay window. I purchased a NOS Backglass from John's Jukes, but then had a problem: what to do about the replay window? I didn't really want to add a decal that might damage the area around the replay window if it was removed at a later date. I inspected the circuit for the added ball and noticed that it still pulsed the (blank) credit unit in the head, which is where it keeps track of balls to play (normal play continues when the credit unit hits zero). I swapped the blank credit unit number wheel with a CC replay game's number wheel from the same era, and then the game told players how many extra balls were left to play.

That's right, forgot! (Been a few years) - for Twinky they used a separate apron for AAB games with a huge insert above the drain that said same player shoots again. It would not be used in replay mode as I seem to recall there was no way to earn an eb in replay mode. I've seen other Twinkys with a standard CC apron.

That apron appeared factory, but I'm not sure if they actually shipped the game with the other changes to the glass and credit reel.

Well I seem to recall that the credit unit had a zero circuit to allow for multiple steps/balls to be built up. Player would not switch until all EBs played.

That was my experience with a Twinky I owned. See a few posts back in the thread.

Is the score motor in a normal resting position? Even if the motor is not able to rotate under power, it might be mid-cycle and could blow a fuse pretty quick if it was powering a bank reset or something. Even if a switch appears to be in a proper detent, it might be 90/180 degrees through the cycle and crucially hitting some switch that is trying to do something heavy.

The lock relay (which should remain unpowered until the left flipper is pressed), anti-cheat relay, coin relay might all have issues. Defeat those circuits then try again. Re-add them one at a time if the fuse lives.

Another thought would be checking the transformer voltage. You probably wouldn't get insta-blow on the fuses if windings were shorted together unless a lot of them were (probably). And there would be clear evidence of that (goo around the bottom of the transformer). Regardless, you can check that level by measuring transformer common to coil power lead on the transformer - this might not work well because of everything that's unhooked, and everything that remains hooked up, so don't worry too much if it seems crazy. If it's way too high, you have your potential partial culprit.

If your game is fitted with a mechanical coin counter, the coils in those can burn as well.

High tap on this game is a physical move of the coil output lead on the transformer to another lug.

Good luck, and happy hunting!