Marx Circuit Breaker

Go out and purchase a Bulb.

Your case is the return or ground.

That's how things were made way back then.

Good luck,john 

A lot of them don't work anymore. Radio Shack use to carry bulbs but there are very few of them left. Wouldn't hurt to try looking at A Lowes type store.

The Marx circuit breaker is simply a circuit breaker with reset button with a 12-14 volt bulb wired across the breaker terminals.  When a short trips the breaker, the voltage is interrupted to the track and goes across the bulb lighting it.  I had one as a kid. 

I added a 6 amp circuit breaker with reset button and light across the terminals for each Lionel LW transformer on the control board to indicate when a short occurs.  I did not have room for the Marx circuit breakers.

Charlie

The bare wire in the 3rd photo goes to one of the terminal posts...where does the other end go to?

I wouldn't trust it to work right without taking the whole thing apart to check for bad insulation and rust damage, and to find where the loose wire is supposed to connect to the breaker itself.

Oops this didn't  post. A few hours old ; hope it's relevant.

Ace is right.

How can you reattach it if it's not apart and accessable?

If any brand were to have a variation nobody knows about, it's Marx, seeing inside would be key for a answer delivered with certainty.

If you are afraid of breaking the tabs, and have a soldering iron or micro torch, heat those tabs before you twist them open. Annealing steel with heat softens it some and they will be less likely to snap off.

If the internal breaker is shot by chance, a self resetting breaker from an auto parts store (Napa) might fit in it. So might a manual one. Size it to your biggest draw, but less than the transformerl limit.

  If the transformer has no breaker in it, plug that into a power strip with a built in breaker ALSO!

The auto parts store is a decent local place to find some bulbs, if you need it right away, and don't mind paying too much for them.  You'll likely save over 50% up to 70% + if ordered from a good supplier. Even Radio Shack is about half the price, but auto parts stores are everywhere.

Found what I needed at a place called Mac's Electronics on E Street in San Bernardino CA.  This guy carries much of the old parts many of us are familiar with.