What size bolts holds the steering wheel on a W124?
 

I am going to the pick n pull and am looking for a new wheel. What size socket/wrench will I need to pull the steering wheel. Thank you!

You will need to remove two torx that hold the air bag into place. There is a giant allen bolt that holds the wheel in place, you will most likely need a cheater to remove it. I don't have any of the sizes offhand.

Also a pipe or shovel handle to put in the spokes so that it doesn't just spin after you break the steering lock:). Test fit it at home first, along with your allen drive and the proper extension length.

Any special precautions when handling the airbag? Disconnect battery and ground myself before handling air bag. Anything else?

If the bolt has been put on or replaced with thread locker you may find heating the bolt with a propane torch necessary. On newer models the fastener is 10mm socket head.

for airbag, key in off position, remove negative battery cable, disconnect the red connector in the right footwell (covered by the metal foot plate), disconnect airbag. Install is the reverse. I store the bag under the car while working on other stuff.

steering wheel removal
 

A car at a U Pull It will not have a battery in it.

The torx is T25, but also take a T20 for good luck.

The allen is 14mm, but also take along a 12mm & 10mm also for good luck.

Bring your 1/2" drive breaker bar and maybe the 1/2 to 3/8 adapter to fit your 14mm allen socket, and like they both said above, long cheater bar for as much leverage as possible.

I'm going to try to pull the steering wheel off a 94 E320 at a U Pull It this weekend:)

Yes, it must be a locktite compound they put on the allen bolt thread. I did the same thing you suggested, standing outside the car, I put my half inch breaker bar on the allen tool, and my floor jack handle between two spokes. It took a lot of pressure to break that allen bolt loose. I was wondering if heating it up would have melted the locktite.

That's why I mentioned it. I had a 24" breaker bar but no suitable extension and could not loosen it. I applied a little heat with the torch and it came free easily.

The allen is a 10mm. Counterclock to loosen. MB quality thread locker on there.

Torx T-30 for the airbag