Yes, you'll need the wiring harness and the ECU. There will be some other work you'll need to do as well and you may also need to replace the portion of the chassis harness which runs along the driver's side fender... I can't recall if the injector resistor pack (which the 89+ non-turbos don't have wiring for) is on the engine harness or the chassis harness.
You'll also need a drive shaft for the GTE's R154 transmission (if you swap the transmission). A stronger fuel pump, oil cooler (I recommend a custom full flow setup over the stock setup). It'll be a little easier for you if you get an '89 or newer engine as a number of things have changed between '88 and '89.
Look through the FAQ and search the board, this has been discussed very in depth many times before.
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