Ugh. I got at the connector for the ignition switch, unplugged it, removed the ancillary connectors, fished it up to where I could reach it, and tested the switch with a DMM. The switch tested 100% as specced. Thinking I might have a real problem, likely mouse related, I reassembled the connector, plugged it back in, etc.
On a whim, I decided to give it a go starting the truck. It started. While I'm over the moon that I'm not currently rolling around under the dash looking for mouse-eaten wires, I really hate it when something that wasn't working starts working without a good explanation.
The gauges are reading sane values when the truck is running. The wipers work (on high only). The windows work. 4WD works.
So what do we think? Intermittently bad ignition switch? Maybe they did replace it, and the new one wasn't well-seated? I don't need to plow, so it's decided to work?
Are there any markings on the switch to indicate if it's an OEM part? Should I order a back-up one so that I have one on hand? Has anyone got other thoughts or suggestions that they want to air?
I've been in a similar situation where I removed a plug from a connector in order to
perform some voltage or resistance checks, find nothing wrong, reconnect everything,
and it then decides to work despite the fact that I didn't do anything besides disturb the connection?
Instead of immediately declaring a victory, we used to use the 2 x MTBF (Mean Time Between Failure)
rule. That is, if something failed on average once every three tries, then we would wait for 6 straight
successes before declaring a fix. (Believe it or not, this helped preserve our reputation with non-electronic
types in our chain of command, for oftentimes the intermittent would return...but no harm, no foul, for
we hadn't declared a fix yet.)
In English, the unknown mechanic that preceded you may not have gotten a solid electrical path between
connector & socket? Myself, I would try that switch at least once a day for a week straight (with zero
misbehavior allowed) before I would start to trust my theory that it was a marginal connection that you
corrected during your troubleshooting session.
Definitely keep us in the loop. This way we all learn from your hands-on experience. And for what it's worth,
I am a firm believer that even a plow truck can (& should) have a reliable electrical system in it. Just takes an
owner like yourself who's willing to verify the electrical functionality of the ignition switch with a DMM.
If it stays working, great! If not, just post all the symptoms and we'll try to narrow it down as far as possible.
Best of luck with your plow truck --