Most OBD2 scanners won't work even if you had adapters for old plugs.
Some older often discontinued units from Snap-on etc could "speak" many protocols for non-standardize "OBD1" computers.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
If you can find an AutoXray 6000 (or maybe even a 4000) on eBay, it will read most any OBD1, like the Fiero, and will also do most OBDII. It even reads my 4.9 swap. Provides sensor data and fault descriptions. Not just trouble codes. AutoXray is out of business, and it's no longer supported, but my 6000 has never failed to talk to any car I've needed to mess with - from my Fieros, up to my OBDII GM stuff, including CANBUS vehicles. I forget if I've tried to use it with my 2019 Ram, but I'd be surprised if it didn't work for that one, too.
I purchased an Actron CP 9690 that will read our old computers. The unit will also read new cars so that closed the deal. On my 88 GT FIERO, it worked well and gave me trouble codes. However, unlike the original Pontiac Scanners, it will not give voltage readouts for the engine components. My TPS was having trouble and the Service Manual wants it adjusted to various voltages. I just used the Bubba Method and keep bending the lever till the engine ran good.
