Ah,
maybe that was what I was remembering, Grass...

Well, after comparing diagrams, it's close: the '89 ECU has different pinouts, but almost identical functions. And the engine harness SEEMS to reroute those pins to the appropriate places.
You're right, the dizzy IS different.

So now, time to flop the harness out and see if the interconnections to the other harnesses are the same. So far the only concrete difference in the rest of the truck is the power supply for the heated O2 sensor.

As to "Why?"
'Cause it's my sick idea of fun,
'cause the EGR manifold is cracked, and rather hard to find,
'cause the 90-91 was good for a HP or 2, and supposedly got a MPG or 2 more... at least on paper...
'cause, if the harness will plug in, it's a 2 hr job, max!

Will I ever get to it? Hmm... that's a DIFFERENT question!

<img src="/forums/images/graemlins/lol.gif" alt="" />

Toby