The no lights on the playfield is probably something on your HOLD/TILT relay if not the obvious answer of the GI 6v line itself or the fuse to the playfield, or fuse holder.
As for 100 point switches, they are designed to directly pulse the score relays without even running the motor. A lot of times this signal will run through the switches on the motor (which is normal as they are normally-closed and the motor is still) to ensure you don't have another action in progress, but it by no means has any relation to running the motor, UNLESS the switch also performs a secondary action/reward like adding bonus or something of the sort. The fact that they are starting your score motor (like a 500 point switch would as it needs the multiples) is troubling.
To confirm this for your game, I looked into your machine's specific schematics. Since it is a Bally game and not a Gottlieb (damn trademarks) you can acquire a free digital copy here: https://ia800700.us.archive.org/10/items/hokuspocusmanual/Hokus_Pocus_Manual.pdf
Here are the following things that will make the score motor spin:
As shown in the image above, the 100 point relay ITSELF does not start the score motor turning - it just cannot do that. So something else is, unless you have a plug plugged in wrong which totally messes with where everything is supposed to go and then obviously the schematic would be largely incorrect to the current state of your machine and "anything goes."
An interesting little factoid is if the motor is endless looping due to some other fault (or rigging it up that way) and you activate an 100 point switch, sometimes I have seen that while the 100 point relay is live the pulsing will cause it to ring up 500 points or maybe even the effect of "infinite points" that you are seeing in a weird scenario where all the stars align. Naturally, the score motor is not supposed to be, nor is expected to be, turning at certain parts of the game. So when it does turn erroneously and other switches are activated that "think" the score motor should be stopped, weird things can happen and "anything goes" yet again. The switches acting weird when the score motor is locked on is not a problem in itself nor something you can fix, rather the focus is on fixing why the score motor is turning erroneously in the first place.
Like I said above, the 100 point relay itself or an 100 point switch that solely awards 100 points CANNOT activate or lock on the motor (unless the "reason" of the equation goes out the window: major wiring fault, plug plugged in wrong or upside down, yadda yadda), even if misadjusted or dirty. So the problem lies elsewhere than in those relays.
It could either be the vibration causing the score motor to activate and lock on through a switch that is gapped too close. But also, are you absolutely sure you are pressing the 100 point switches and not the 500 point switches, or a switch with a "double feature" that gives 100 points AND does some other kind of action? It would make a lot more sense if it was initiated by a switch that is supposed to turn it on, and THEN faulting, rather than magically coming on when not supposed to at all.
I don't know Hokus Pokus well enough to know the answer by heart, but according to the schematic and the image shown above there is nothing that I feel like you could mistake for this except for if the A-B-C-D rollovers give 100 and you are pushing those, which would explain the motor activating.
Lastly, two things. Adjust your score motor's "home position" switch which is what tells the score motor is has completed a revolution and to stop spinning unless there is something else telling it to keep going. This will make the fault a lot smaller and also let us know if the score motor is running itself into oblivion and something is just turning it on momentarily, or if something else is running it into oblivion. My final statement for this post is a question, when the reels do this problem and keep clacking away, are you hearing bells/chimes (assuming they function and the score relays are adjusted and cleaned well), or rather, are the point relays that control both the reels and bells/chimes firing or is it straight to the score reels?
The reason I ask this is because if the bells/chimes aren't firing (again, assuming they work normally), this means the point relays aren't the things firing the reels, which means the problem might lie more in the reset section (which pulses the reels in their own circuit directly rather than using the score relays as this would set off a horrendous bell palooza during every reset.)