Your distributor is different from my '89 so I don't know how to test it - but it sounds like either the optical unit in the distributor or the power transistor is bad. There are a couple of posts where I detailed the test for the power transistor. Here's one:

Power Transistor Test

Use the search feature and see if you can find some more info on it. Also, Conner has a few posts on testing the distributor, so check for those under his name. I suspect he'll respond to this before long.

Good luck,
Frank

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum