Where are some key spots that i should check for power with the key in run/start to verify the ignition switch is good? trying to diagnose an intermitted no start and key run/start the Pink 12v always-hot is live with good voltage (10v crank 12.6v run) to both the ICM and Coil, as well as the 12v lead to the Crank sensor though i have not checked for power during crank down there. i have also checked continuity between the White w/Black stripe signal wire from the ICM to the Coil, but not the signal wire from the CKP up to the ICM.

 

I know you asked about the ignition system specifically, but all power comes from the ignition switch which has been a failure point in many s-series trucks over the years so you might want to start there. For that, the ignition switch wiring harness main connector under the steering column is the best place to test all of the contacts in the ignition switch. If you don't already have some back probe tips, you might want to get some before you start as you'll need to be testing these terminals with the connectors connected. You can test straight up voltage as well as voltage drop across the various contacts while under load. Voltage drop across the contacts should be very low. If it is high and/or fluctuates a lot, then the contact in question is likely compromised. The Anatomy of the Ignition Switch tech article link in my signature runs through the relevant wiring diagrams as well as what exactly is inside the ignition switch.

As far as the ignition system itself, I'll do some more digging tonight. Are you sure that you aren't getting spark?

 

Positive, Though i lack the tools to check directly (spark tester, will have one within the next couple of weeks) before i go off buying new tools as much as i like an excuse to do so i want to rule out everything else, the motor is flooding itself with a known-good regulator, it has MPFI injectors and even disabling the fuel pump and trying starting fluid it still refuses, timing both distributor and valves was checked with the timing cover off and all lines up, Cap/rotor/wires are fairly new and i did go through and test terminal resistance (came out to about 1.7ohm or there abouts) to check for an internally broken terminal. although i did notice the sound when cranking is different with the ICM/Coil plugged in vs unplugged. so something is getting spark atleast some of the time. this thread is related to the diagnostics for This thread.

 

Replaced switch, rotor and cap, and she sings damn well. took it on a short drive, outside of usual oddities expected with a 20 year old truck thats sat for a while she feels good, runs decent save for a very slight idle misfire i believe to be related to the distributor retard and the exhaust leak. Changing the plugs out for the Delco 993 Iridiums tomorrow. Thanks y'all.

 

Take a good look at the rotor you removed. Mine had a tiny hole burned through it when I bought my Blazer, and it wouldn't start. A new rotor fixed it right up.

Not that it really matters at this point, but it's always nice to know what failed.

 

my truck had a slightly similar issue except it seems the previous owner tried to plug the hole with nail polish or something. the difference being my truck would start horribly and then encounter a leanout stall with throttle input.