According to this web-site -> http://www.flippers.be/basics/101-interlock_switch.html, the Interlock switch was introduced "somewhere during the production run of the Twilight Zone pinball machine". Is it possible that my machine is an early production model without an Interlock circuit? 
I have never seen the message "Coin door is open Coils and Flashers are disabled" on the DMD when the coin door is open, and according to that same web-site, "You can also see it's installed, the difference is that now there are 2 switches left inside the cabinet that the coin door closes. Older games only had one switch.". My machine only has 1 switch 
Matthew
That's what threw me the when you first asked about the solenoids not working. TZ should have two - but you have one. I'd say that you are correct - If you do not see the message and do not have the switch, then your machine does not have the interlock capability !
So if you put your machine on eBay - You CAN mention it is the "RARE" TZ 
What is the purpose of the switch I have in my machine then? I have disconnected it and I can't see any difference!
Matthew
The door switch simply enables the coin door switches. Thats all it does !
I believe that this is correct.
Your TZ was definately an early production. I was thinking that it may have been prototype at one stage as it had the original clock decal and factory playfield holes for the extra posts in the pop bumper area.
Apart from the missing interlock switch which appears factory, I recommend you still turn off from the mains when you have the playfield up as there are many other things that can be shorted.
Thanks Dave, I usually turn the machine off at the mains when the playfield is up, however sometimes I leave the machine switched on when the playfield is up to diagnose/investigate issues. I did that recently when I needed to adjust one of the pop bumper switches, it would have been a real PITA to continually raise and lower the playfield after every small adjustment. But in general, playfield up = mains off.
Matthew
