Weirdest problem of the year. ECM I think is the problem

Hi Guys, I have a 1988 B2200 5spd reg. cab with 88,000 miles on it. When I drive it down the road for about 10 min. it will shut itself off. I mean the engine, radio, dashlights, everything goes off. Just as if you, as a passenger were to reach over and turned the key to the off position. Here is the weird part. All I have to do is actually turn the key to the off position for about 5 sec. and then back to the On position for about 2 sec., then it starts right back up and runs fine for about another 1/2 mile or so............ My workaround has been to turn it off at red lights. It always starts back up and gets me to where ever I need it to go....The longer the redlight the farther it will go before it shuts itself off again. I think it is something in the ECM unit that is heating up and the brief time I turn it off helps cool it down to a temp within a range that allows it to run..

Besides this bit of weirdness I love this truck, it runs like new.

Actually, I betting otherwise. The ECU is only involved with carburetion/emissions, not radio, dashlights, etc.

I'm betting the problem is the electrical part of the ignition switch. In fact, the very same thing happened to my 1988 B2200 at about 79,500 miles, and I described exactly the same: like someone reached over and shut off the with the key. This part frequently goes bad on these trucks as they age, and is not a tough fix.

The part of the ignition switch with the key cylinder is NOT involved. One can take off the upper and lower steering column plastic covers and drive it, then next time the truck dies, leave the key in position, don't touch it. Then test with a voltmeter or 12 volt test light in this condition, great way to isolate this, as the wires and their solder points are all exposed.

There should always be positive voltage in the white wire. In the "run" position, the blue wire, the black with yellow stripe, and black with white stripe should all have positive voltage.

In the "start" position, the black with yellow and the black with red should have voltage. So just because the engine will spin in the "start" position does not mean that the electrical part of the switch is OK.
The part number for the electrical part is UB3966151.

Oprah - you're new here, welcome. I've had my '88 B2200 for 17.5 years now, and was a mechanic before I got into the chemistry analysis business, but work on all my vehicles. The trick is to work systematically, find out/test what's wrong, and not just throw parts at it.

Exactly what Cusser said plus watch out for big keychains or any extra weight hanging of the ignition switch.. that also causes premature wear