I've read that this 98 pcm will 'fit' in the location of the stock Ecm.

SO... If i do it this way, do i use the bulkhead to connect everything together?

Or should i mount my PCM in the engine compartment or in the trunk?

The stock Fiero "bulkhead" connector isn't a connector at all. All it does is provide a sealed "pass-thru" the bulkhead/firewall. There are actually no wiring harness connections inside. It is factory assembled over the stock wiring harness with heat activated sealant/glue. This means you can take it apart if you heat it up (with a heat gun) and remove it from the factory Fiero wiring harness and then separate the glue from it so you can reuse it on another harness.

After removing it from the Fiero harness, you can install it on the harness you custom make for your 3800. I do this in all the swaps build. I custom modify the stock 3800 wiring harness to run thru the firewall in the stock location so I can mount the 3800 PCM in the stock Fiero ECM location. After you are done with all your wiring work, you can seal up the "bulkhead connector" with the RTV of your choice (I use Permatex Ultra Black in the full size caulk tube so I can squeeze enough into the bulkhead connector to seal it properly).

-ryan

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Oh i never fully understood.

I'll have to think this through more. My plan was to build the entire harness and have it ready to plug and play on install day.

You still can have you harness already to go and on instal day remove the old bulk head piece and put it on the new harness and fill it with good high heap silicone or epoxy to seal it back up. I find cutting the bulk head piece off the old harness and tossing it in boiling water for a few minutes makes separating the two halves very quick and easy. Dan

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DARN Cars now open with
Over 30 years wiring experience between cars and trade as an avionics technician in both Canadian Air Force and civilian aviation.
Over 25 years experience building and modifying cars.
Over 10 years of full Fiero engine swaps and harnesses building and still going.