You got a transfer of power problem. You have checked your fuses to be good but also making continuity through the fuse holder and through it to the playfield?

Not necessarily. Can explain in detail later. But you should have power at the input of the fuse holder going through the playfield fuse to the playfield lights when the machine is turned on! If you do not you need to trace backwards.

If I was home I would look at my ‘75 Gotlieb and give you direct info.

Don’t want to dive into switches and relays if it is a bad connection.

What's the Tilt Hold (H) relay doing when this happens?

Here is where I would check.

1. re-seat the playfield jones plugs. Checking to ensure there are no loose wires. (focus on the white-blk and black-white wires)
2. Check the 10 amp fuse and fuse holder for the playfield lights (white and white-Red wires)
3. Check and clean the H relay switch with White-red/white-blk wires

I suspect the H relay or the fuse holder. after twenty minutes of playing, may shake the machine enough to get a better connection.

Is the Tilt light on when the playfield lights are out?

Ok the problem your having is your playfield lights are going out while machine is on after play has ended for about 20 minutes correct?
1. Playfield lights do not come on when machine is first turned on until a game is started. That is normal function.
Need you check for loose connections on any tilt mech. Even the tilt mechs theirselves for abnormalities.
I will look into schematics further later.

The H-relay should hold itself on unless the tilt it triggered.
I would Clean and gap these switches.

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Ok your tilt relay is probably getting tripped from your trip mechs( you have more than one). If you made sure you have all good connections. See while your game is in play move all your trip mechs to see if they all are working. If you can trip this relay without actually moving the trip mech problem could be solved quickly like moving a wire connected to mech. Remember a dirty switch doesn’t need solid contact to activate.

Yes. You should have one on the door, two in cabinet, one on playfield and maybe one in back box. At lunch I will open my ‘75 Gotlieb and let you know when I get back home.

Well your tilt will not reset until a new game is started. That part tells me your reset is functioning properly. Not home yet but I believe there is one in the back box (the head). Now that connection pass through your jones plug. Disconnect and Make sure the pins are clean the reconnected.

Also there should be one in bottom of cabinet by your score motor( it is round with a bunch of switches on it) the tilt mech should be around that area.

Yes someone cut a hole and bent it for some reason. lol! They could of just raised the leaf block. Ok try this since your just learning put a piece of paper of business card between every tilt switch on contact to make it in operational and see if the tilt relay trips by itself after a game is finished.

Back box tilt switch. Far right side half way up.

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Whoops wrong on sliding card in between tilt switches. Only do that if switch is normally open. The closed tilt switches clean them with a card or very fine grit sandpaper then clean with a card.

Just looked mine has a cut hole under it but not bent up like yours. Wonder if it has ever been replaced.

Yep mention in my post before your I made a mistake on that.

Ok there are three switches that are anti-cheat that are normally closed. (1st image)
One on the coin door, one in the lightbox and one called the Bounce switch on the mech. board.
Check the colors and make sure they are closed and making good contact.

There are also 3 tilt switches that are normally open. the ball, pendulum and one under the playfield (2nd image)
Check the colors and make sure they are open and are not too sensitive. Normally the playfield one can be 1/2 inch or more apart.

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Yep go back and redo what you did make sure the closed tilt switches are clean and closed.

Off topic- are those pinup matchbooks on the wall near your game?

Double check that tilt switch by score motor. It should be closed. Someone has bent that switch before and might be your original problem in the first place. They might of bent it to get a better connection. If you cleaned it it could of reopened it.

I’ll send a pm. Playfield and headbox tilt switches should be open.

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Don't confuse the anti-cheat switches with the tilt switches.
Anti-cheat switches are usually NC, and when they open, they drop out the hold relay. This effectively shuts off the game.
The hole in the bottom board below the lead weighted slam switch was done at the factory.
All games of this era have this type of arrangement. As long as this switch is closed and making good contact, it shouldn't pose any problems.
Tilt switches are usually NO, and when closed, trip the tilt relay, causing the tilt light to illuminate, and the playfield power and lights to go out.

So when ever it tilts after next ball does the playfield goes out or is the tilt light just on?

It could be that only the tilt lamp is staying lit. Does the game have playfield power otherwise?

You said you cleaned the tilt hold relay switches? How did you clean them? Some where today you have came across your problem if it was a switch or wire you messed with or touched it. Now we need to isolate it.

Did you clean contacts out good with a business card or playing card to get all grit out afterwards?

Can you manually activate tilt Hold relay and cause the tilt light to go out?

I think this might be deeper. At the beginning I was hoping a bad connection that was putting it in a tilt condition. Now I believe your control bank relay switches are not holding your TILT HOLD relay in normal operating condition. Your TILT relay does not activate unless open tilt switch like the bob tilt closes. I believe Relay ZB and SB1 in control bank is connected to tilt hold relay if you want to know what activates it. This control bank can be a pain in the ass to clean switches on its relays and those switches do get really dirty after a while. A cardboard cover folds over it to protect it from anything that might drop on it. Small burnishing tool seems to get in the small spaces for me. Especially if it is just one switch in the back of eight switches. If that rack gets just slightly out of alignment a person just wants to walk away. Kinda hard to point you right to the problem. But if you can track down the control bank relay switch that connects to tilt hold relay clean them this probably would solve this problem. If you shine a light on these switches and relays and there covered in coil dust you might want someone that had some experience messing with this control bank. I remember my first time cleaning a hard to reach control bank switch. First time I did it it working for about a hand full of plays. By the 3rd time into it I thought I was over doing it cleaning the contact but it has not been a problem since. Mine still has coil dust all inside control bank but I go by if it’s not broke don’t mess with it on a Pinball machine!
If i lived closer I help you fix it. Two way problem is it being activated into tilt condition or is it finally not resetting itself into normal non tilt function. Good luck!