My base model D150 has a non-tilt steering column.
The turn signal stem switch controls turn signals, (pull back) high beams, and (twist) windshield wipers.
The switch is slowly going bad. I think this configuration is unique to this year, as every 89 I've seen has a different configuration, and every 1991+ does as well. m probably wrong, but I digress, as 91+'s are hard to find.
I'm not trying to be stuck, but, am I? Do I have any options?
The truck is a 90 D150, former forestry service truck, (Forestry Standard paint code 35350) with 109k miles, 318, 727, with only available options installed being a/c (not working) rear cargo light and map light.

 

Have you looked to see if it's available anywhere?

 

i looked, to no avail. Maybe you know somewhere i don't?

 

There is better parts support for the tilt columns, because they are GM-based and used for 20ish years. 91 is a major change and shares parts thru '98 (or so) Rams.
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You may have to score a whole column from a parts truck.

I have had exceptional luck finding 88-90 trucks. Seems like there's two major camps - the guys that like carburetors, or prefer the bells & whistles that came on the 91-93.

 

If can't find anything on RA or any of the chain stores then get the factory part # and see what google can find.
I found these but can't be positive they are correct.
04443944 (MULTIFUNCTION) w/Intermittent Wiper (Use Insul. 4419577)
04638033 (MULTIFUNCTION) w/2-Speed Wiper (Use Insul. 4419577)

 

You're not completely stuck, but your setup is indeed unique to 1990, and your options are limited without adaptation. All you have to do is search for the right part or adapt a later component with a little work.