Looks like it might be the end of the road for my MB. Had to put a push-button switch for the starter, which wouldn't crank with the key. The blower stopped working, and the A/C & heater stopped working.
I put a new steering lock & ignition switch and key set in. Finished up today. Same as before, nothing works yet.
Any more ideas?

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1984 MB 300SD Turbo

Step one, is there power to the ignition switch? From the ignition switch?

When the going gets tough, the tough get going. There are a lot of resources both on this website and others to assist you. That said, a second set of eyeballs never hurt anything.

Either a friend who has mechanical knowledge or call around to the indy repair shops and ask what they would charge to perform a simple diagnosis. I've use them every so often and it tends to speed up the process.

TIME IS MONEY.

Take it to an MB mechanic. The ignition switch circuit on this car is very simple, but it helps if you have the factory wiring diagrams.

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1998 E300 turbodiesel

America's Rights and Freedoms Are Not The Enemy!

Since all of the circuits that are not working are powered from the key switch and you've installed a new one, the original key switch was not the issue. For whatever reason, you don't have 12V present at the key switch. Get a wiring diagram and find out why! Some of the W126 cars had 2 separate 12V feeds to the key switch up under the dash. They connect to a junction block. You could have a poor or failed connection there if your car has such a connection.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Bad shift rod bushings can prevent disengagement of the NSS (neutral safety switch, aka starter lockout switch) or the NSS itself may have failed.

Auxillary water pump may have seized and taken out the CCU (climate control unit) traces.

I also had no heat and a non-functional blower motor in my 83 W126 300SD.
The fix was to disconnect the auxillary water pump, and replace the bad CCU (had burnt traces) and the bad temperature regulator (had two dead relays) with used junkyard units.

The blower motor runs fine when supplied with voltage.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Just replacing parts without diagnosing the problem is almost certain to bring such frustrations. You don't even tell us what year your car is. Details matter.

The NSS is a common "won't crank" culprit (on many cars) and very easy to trouble-shoot. Indeed the whole starting system is easy to diagnose. That is true on all my vehicles except the 2002 T&C which has a key security "feature" (termed SKIP) which can disable the engine.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Yep, diagnose rather than randomly throw parts at a car.

Gain an understanding of how systems work and how to test them.