Much as I love Paragon, machines of this age need all the recommended fixes suggested in the PinWiki to make them reliable.
Here is the pinwiki section on Bally Lamp problems:
https://www.pinwiki.com/wiki/index.php/Bally/Stern#Lamp_problems
The above suggestion to 'Reflow all boards, Repin all connectors' is crazy hard, an insane amount of labor, and absolutely correct. (Though reflowing for me means to reflow lots of things on the board other than connector pins... all connector pins need to be replaced as well as all the terminals in the plugs.)
At this point for machines of this age, to make this reliable you are faced with a LOT of work.
Personally, before I would offer a machine of this age for resale I would do the 36 pages of recommended fixes, probably replace the rectifier board (new pins and plugs here are absolutely necessary), repin all pins and plugs to all boards, and strongly consider replacing every lamp that is under an insert under the playfield with a Yoppsicle.
Yeah, it's a lot.
But it's your machine. Wiggle some connectors, keep it going for a week, month, year. It might stay reliable enough for you to keep playing for a while. It may be possible to bring your machine up by just replacing the fuse associated with the controlled lights, this doesn't address the underlying reliability problems, but you might get it working for now.
Read the Wiki about your lamp problems, and let us know if you have any problems.
If you need us to help you step by step, the first thing to check is the fuses, particularly fuse F1 on the rectifier board, lift one end of the fuse and test it with a meter, you can't tell visually if a fuse is working.
On the rectifier board make sure you are getting around 5.4v dc on test point tp1.
Then let us know what you find!