Confused by Lionel Electric switches 5122 need help

Sounds like you might be missing the insulating pins on the inner rails of the main and the turnout.

Here are the installation instructions. I've got 15 of these on my layout and they work fine.

Bob

Thank you Bob, I have see those instructions and I did have the insulating pins in those spots. Do you have a fixed power supply for your switches? That is the only thing I think I haven't tried yet.

Mine are on track power. These can be re-wired for accessory power but it's a bit involved and I'd have to take them off the layout.

Yes, I know what you mean and I would rather NOT re-wire them. I installed the insulating pins as shown here in the directions but still once the locomotive would cross, the rest of the cars derailed. I just don't know what to do  

Couple of thoughts. 

1. Make sure the insulating/fiber pins are inserted where I've marked here in red.

2. Remove the switch controllers and try your setup manually. I can't help but wonder if you've got one or both of the switch controllers connected to the wrong posts. Then attach one, retry, and make sure it works with one switch. Once one switch is proven to be working, then connect the 2nd switch controller.

3. If 1 and 2 don't solve the problem, try removing one of the switches and replacing with straight track. See if the remaining switch works. Then try the other side and see if the 2nd switch works when it's the only switch on the board. I've had issues with past layouts with back-to-back switches. If space allows, you might have to add a partial straight track between the two switches. I can't explain it, but that has helped me in the past with PW 1121 O27 switches.

That's all I can think of.

Disconnect the controllers and run your trains. If the switches still throw by themselves, there is an internal problem with them.

Larry

All the replies so far have very good ideas to possibly solve the problem.

You mention you have heavy old Lionel cars that derail on the switches. If those cars are postwar operating cars with sliding shoes or have sliding shoes to operate the couplers, sometimes the sliding shoes get snagged on the switches causing derailments.

Please specify what you think is causing the derailments on the switches. 

If you run the locomotive alone through the switches, does it derail every time? You original post says the locomotive goes through the switch and then the cars derail.

If you have the track power on and slowly  push with your hand each car through the switch, does each car derail? Do some cars not derail?

Arnold