Looking at a S420 what should I look for
 

I will be looking at an S420 this weekend. Anything in particular that I should look out for?

Also how do you read codes on these vehicles, since it is a pre 96 model where the obd2 does not work?

TEST EVERY switch/feature/function and button. Lol. S-Classes are like the Apollo spaceships when it comes to gadgetry which means everything is $$$ on them. If it has got maintenance and there isn't more than a half dozen features that don't work, go for it, depending on the price of course. :)

You said it well. Also make sure it comes with recors, get a PPI and look out for any rust and cracked bumpers. Get a long test drive and make sure that air suspension is working 100%. If not you could be facing some serious money to fix.

If it is a 94-95; check the wire harness and ASR issues (limp mode)

It wouldn't necessarily have ASR or self leveling suspension. Both were optional, and both should be avoided, in my view.

This a 95 that has just over a 100K on it. They guy is asking 2000 for it because he said he drove into a snowbank. The damage is a broken headlight cracked bumper, dents in the fender. But he stated that everything else is in very good condition. I am figuring if I can get the car really cheap then I could fix the couple things on it and see how it goes.