I don't own one. Having said that, I looked at the two harnesses online and it appears the only difference, beyond coil connectors, is the brown jumper on the 88864. So the 88863 is for a waste spark application, the 88864 is for non waste spark. I think it goes like this: On the 88864 because of the jumper, the system will not do the waste spark. If you ALSO turn off the waste spark in the computer, there should be no difference. But, on the 88863 harness there is no brown jumper and the system is set up for waste spark, because that was stock. If you wish to turn off the waste spark, you have to turn it off in the computer.

Make sense?

In general, when making modifications, when the item stops working, one undoes or redoes the last thing changed. What was the last thing you changed?

R.