People have said in setting the base timing that you have to disconnect the ESC(I think thats what it was called) but in a book I have all it shows is when the vehicle is running you connect the A&B terminals while adjusting the timing then before shuttingoff the engine you remove the jumper and shut the engine off. Which is right for an 89 L98?

 

I've never tried jumping the terminals. There should be a single wire thats tan with a black stripe and a single wire weatherpack connector that you can disconnect for setting the timing. I dont know where it would be on your monte since they didnt come that way
The painless harness has the connector about 6-8" from the ECM itself. The factory F-body harness its more like 4' from the ECM.

 

My friend and I just set my base timing yesterday. We did disconnect the EST (Electronic Spark Timing) and just turned the damn distributor to the desired advance. I think what the book is telling you is how to adjust the Electronic Spark Timing (computer controlled) and what you wanna do is adjust your base timing. Good luck

- Tom