I know you can just swap the minivan harness over, but that requires money that I don't have, and finding a turbo mini that isn't hacked at the junkyard. People seem to love to chop up the harnesses on those things. Tracking down loose ends and changing every wire in the engine bay is not my cup of tea, especially when I've shelled out $50 for something that should be plug and play. So here is my trial and error route to getting an L body wiring harness ready for a turbo (or MPI without turbo, if that's your thing).
This will come in probably 3 parts, #1 being general and ignition, #2 being injectors, #3 will be anything else I forget. I've got part 1 done so here goes.
Parts for this step:
Turbo distributor, turbo HEP, turbo HEP harness, SMEC connector with pins, turbo ECU.
Tools will include everything you'll need to remove the distributor, battery, and ECU. Wire cutters, drill and small drill bits, and a small screwdriver are also needed.
Things you should be familiar with before you start:
SMEC:ExtraPinInstall - The Merkur Wiki
that doesn't take a rocket scientist to figure out, but it's nerve wracking if your perfectly good daily driven TBI harness is the first harness you've ever drilled.
You should have a good idea about the inputs and outputs of the TBI and turbo SMEC, as well as the pinouts. All that information can be found here
Understanding The Chrysler ECU
go through this pinout
The 1988 - 1989 TBI SMEC - MiniMopar Resources
and one of these two pinouts
The 1988 - 1989 Turbo I SMEC - MiniMopar Resources
The 1988 - 1989 Turbo II SMEC - MiniMopar Resources
Disconnect the battery before you start doing this stuff too. Electricity is dangerous.
Ok, so now you're comfortable with the ECU, it's wires, and adding them and taking them apart. You've noticed that to get it to run (read: function with error codes that can be ignored or sorted out later) you really only have to add a few wires (I only counted 4, but I haven't gotten it running yet). Here's what it will take to get your TBI harness to spark and run with a turbo ECU.
Step .5: If you think better while intoxicated, or think you think better while intoxicated, have a beer or 4.
Step 1: Install and properly time the turbo distributor with the turbo hall effect sensor. The turbo distributor has an open window to trigger the injector sync pickup. Doing this first you can plug in the black plug to the stock harness and drive like it was not ever different at all.
Not doing this first means you may have to add base spark timing to your list of "why won't it start" problems. Not fun, take it from me.
Step 2: Cut the wire coming from position 10 on the 60 way and send it to the output of the Automatic Shut Down relay. This is easily found at the + terminal of the coil. I found that the TBI computer did not care what that wire was doing, but the turbo uses it to sense proper ASD operation and will throw a code. Cover the bare wire that used to go to pin 10 with electrical tape. It is 12v with the key in the on position and would make a difficult short to track down.
Step 3: Splice in the white hall effect connector. The orange wire goes to the orange wire of the black connector, and the black wire goes to the black wire of the black connector. Run a new wire and pin from position 26 on the ECU to the final wire on the white HEP connector. Should be a tan color, but it's hard to miss being the one that's not mostly black or day glow orange.
Step 4: Grind down the tabs that keep the ECU from going in upside down. Now it's up to you to keep it going the right way. Just remember the ugly side goes down.
Step 5: Plug in the turbo ECU of your choice (2.2 or 2.5) and fire it up. Why this works, I don't know, possibly MAP scaling combined with injectors (4 * 33pph vs. 1 * 72pph with a 2:1 MAP ratio). You may need some starting fluid to keep it going if it's a 2.5 TBI, but I can drive my 2.2 around the driveway with the turbo computer.
Trubleshooting: Assuming everything was just fine before this and you got all the wires right at this point:
No spark at all:
Wire from pin 10 not properly attatched to + on coil.
Bad HEP sensor.
4 sparks at first starting, then no more sparks:
Bad connection somewhere in pin 26 or the wires you've made leading to it.
Bad HEP sensor.
You didn't actually have a turbo distributor with the one shutter that has a hole in it.
At this point you can be like me and put the TBI computer back in to get the Horizon out of the garage so your dad will stop yelling at you for having it in there, or you can go on to wire up the injector harness and everything else. I'll be getting to those when I have some free time in the near future. Either way, the TBI computer doesn't care about the extra input or the changing of pin 10.
Readers digest version. Install turbo distributor and HEP, wire pin 10 from the ECU to + on the coil, wire in the extra plug on the HEP with a new pin to spot # 26 on the ECU, make the plug fit, fire it up on the turbo ECU.