Ignition switch test/replace?

[76C10Stepside]

Two questions about the ignition SWITCH on my 1989 Chevy S10. 1) How to test it. 2) What's the deal with replacement switches? I'm talking about the actual switch mounted on the steering column under the dash, NOT the lock cylinder (see photo). My truck has tilt column. If you know how to test the switch itself and/or have replaced it before, I'd like to hear from you. First two pics are of my ign switch and plug, 3rd pic is example replacement part.

BACKGROUND: I have been having intermittent no-crank problem for over a year now (did not drive truck all year). Took to a shop that said starter was bad and replaced it, but the next day, no crankee. It has sat all year, and now cranks/starts, but I can't drive it b/c it keeps leaving me stranded.

I tested all fuses, the ignition/out, neutral safety switch and alternator, and all tested good. Took it to a shop that said the starter had shorted out and installed a new one. It got me home, but next day would not crank (tested alternator after this). Figured it's probably either a wire shorting intermittently, or a maybe a failing ECM.

Paid a mobile mechanic to troubleshoot it. All he did was test a couple things under the dash and in engine bay, then suggest replacing the ignition switch (he did not even know what the part was called, lol, just pointed at it).

QUESTION #1: HOW TO TEST THE IGNITION SWITCH?
I removed the ignition switch (see photo) for inspection and testing. I thought it was just an on/off switch, but learned that it "toggles" between two states. It has 3 terminals. Every other push in/release, I get about 2 ohms on "side a", then when I click again, it goes to 1 ohm. The reading for "side b" jumps all over the place, between 20 and 60 ohms, then get a steady 1 ohm when I click the switch again.

I suspect the wild resistance reading on "side b" means the switch is "bad", but would like to understand how to properly test the switch for both "good" and "bad".

QUESTION #2: WHAT'S THE DEAL WITH REPLACEMENT SWITCHES?
All the local parts stores stock switches with 8 spade connectors. Mine only has THREE and uses a specific plug. Is the replacement switch a "universal application" or something? I attached an example replacement switch (BWD CS83) for comparison.

[ChevyTech]

The two top photos are of the switch for the high beam or low beam headlights.

The bottom photo is an ignition switch.

[76C10Stepside]

Originally Posted by ChevyTech

The two top photos are of the switch for the high beam or low beam headlights.

The bottom photo is an ignition switch.

D'oh!

Thanks for pointing out my blunder! All I have to go on is the crappy Chilton repair manual. Just found a description of the ignition switch (no picture). Book says it's "located inside the channel section of the brake pedal support and is completely inaccessible without first lowering the steering column".

The ASE certified mobile mechanic that looked at my truck needs to go back to school!

Any thoughts on what the cause of my intermittent no-crank issue could be, given the tests I've already run/parts I ruled out (I THINK)? Is there any practical way to check each inch of the wiring to the starter? I could barely even get the starter out/in, and could not see into the tiny area GM provided for the starter for the 4.3-equipped S10s. I chronic injuries (neck, back and shoulder) that make R/R the starter extremely difficult for me. Any hints/tips/tricks welcome!

[76C10Stepside]

Wait a sec... Could it be the dimmer switch? The second time it left me stranded with no-crank, it actually started up, but when I turned the headlights on, it died immediately. This is what lead me to think there is a short somewhere. But that only happened one time (though I have not been driving the truck since then, I have tried getting it to die by turning the headlights on/off with engine running, and could not get it to do it again). After that is when the first shop said the starter was bad. I have had quite a few defective new parts that had to be returned, so assumed the starter was actually dead, but did not confirm this by having the old starter tested before I returned it to the auto parts store).