You'll need to find out why the score motor does not keep running to complete the reset process. The first step is to check the primary switches that send power to the score motor. I don't have a Jungle schematic, so I'm looking at a Big Brave schematic which is similar. Check the following relays and their switches.

D, E, O, Q, S, U, W, AX, BX. The switches related to the score motor "might" have a red/white wire and slate/red wire. Maybe someone on PinSide has part of a Jungle schematic they could share...

You'd have to find the ZB relay coil on the schematic and then trace back towards the switches to see which switches send power to the ZB coil. You can test the ZB coil with a 9-volt battery to see if it's working. But, it sounds like there's also an issue with the player unit that isn't advancing properly... To simplify the troubleshooting, what is happening now when you try to start the machine? You power on the machine, machine is in game over mode or tilt mode, one or more credits are on the credit unit, you push the start button, then what happens? Do all the score reels reset? Also, does the player unit advance easily when you manually push and release the advance solenoid plunger?

You'll need to see what sends power to the ZB relay coil. Again, I'm working off a 1973 Big Brave schematic, but it should be similar. There are five relays switches that send power the the ZB coil: tilt hold relay, 10 point relay, 100 point relay, hold relay and 1st ball relay (ZB). You can check these five relays to see if all the switches are clean and adjusted properly.

Look on your schematic and find the ZB relay coil. Follow the line to the right and you'll see the switches that send power to the ZB coil. You'll see the wire colors for the switches also so you can zero in on each individual switch that is related to the ZB coil...