For the trough switches, it's actually easier to go in through the coin door.
There is a small metal plate (sometimes attached - some operators would chuck it) that protects the trough switches. Held on by one or two screws.
Remove that, then you'll see the switches.
The #1 trough switch (the one in the ball lift chamber) is actually a switch actuated by a metal pin. That metal pin is sometimes lubricated, and becomes rusted or gummy and doesn't pop up and down - it's all based on the tension of the long blade of the trough #1 switch. That switch -must- with a capital M open and close as the balls are lifted and a new one rolls in.
With the game off, you can manually push up on the bar that is connected to the lift elevator and lift up a ball to observe the action. If you do it just a little bit, you can roll it back as well to ensure the ball is actuating the pin in the #1 trough.
The other switches will be actuated by a piece of metal. When the ball leaves the switch, they should change state. If they don't, the switch or the metal piece need adjusting. Note that you cannot adjust the metal piece directly and you'll snap it if you try tweaking it with a pair of pliers. You have to push the leaves of the switch around if it is in the wrong spot.
We'll cross that bridge when we get there.
For lifting the playfield, you have to unscrew the four screws on the perimeter of the playfield (on top), then pull back the plunger and lift using a finger inside the bottommost hole.
When you lift, lift as close to straight up as possible. The shutter motor is in the back and switches on it can get tweaked if you pull too quickly or too much forward. Unlikely to happen on this particular game, but still possible and a good habit.
As you lift up, you'll see the shutter motor. Pull the playfield up and forward (towards you), until it is almost vertical. You should see a small wooden channel on the sides. Pull playfield towards notch in vertical position, then you can lay the playfield on the head, gently. It will remain there while you're looking at the guts.
Note that you should not turn the game on unless you are prepared to catch balls. The game will have no way of knowing if a ball has lifted and just go crazy lifting until there are no more. To stop this, either hold down the shooter lane switch (the one directly outside of the ball elevator) while turning on, or just catch the balls. It's not as bad as it sounds, but surprising the first time or two. If a ball drops down, be careful as it will be near a 120V source for the power switch. Unplug the game before retrieving just to be safe.