Have a 98 harness for an automatic car. Havent purchased the ECM yet. Can I run a 6 speed with the auto harness and does the ECM have to be from a manual car? Another question is, Im looking to convert a LT1 t56 to a LS1 t56 by changing the bellhousing and input shaft. Is the wiring going to be the same? Appreciate any help I can get.

 

Yes you can make an auto run a t56. You just have to run a few wires off the neutral safety switch.

 

The PCM can be retuned to whatever loadout you're running. Trans type is changed by a few wire and connector swaps

Since you have a 98, it has a specific pinout for that year. Now would be a great time to repin it to +99 style

 

I agree with Pocket. Go to a 99-02 PCM.

 

The engine is a 98 as well. What all would need to be changed on it?

 

Nothing, the old PCM controls the same things with the same connectors as the newer PCM

Changes begin when you go to GEN IV engines on GEN III controls or vise versus. The only exception is iron truck blocks require a hole to be drilled/tapped for most non truck ALT brackets