Need a little help

[Bart_3500]

I've had a TBI system on my rig for about 5 years now and it's always run great. I started to change out the 50 some year old wiring harness with a new Centec harness. It didn't include or have anything to do with the TBI system. After getting it back together I had problems. I know the basics of the efi system and that it needed only a couple three outside leads to work. After a lot of trial and error and some help from this site. I got it running. Problem now is that it's running like crap, very rich and surging from 500 to 1500 rpms. The GM TBI I have is for an 88 ish 350. Last 4 of the ECM is 7747. The main problem I had orginally was getting power to the fuel pump. The builder (custom efis) now out of business ran everything in red and black wires so it was fun figuring out what was what. I did and now I have this running problem. Could I have screwed up the ECM? It appears that the IAC motor isn't doing anything because it's running rich, very rich to the point of burning eyes in the garage. I could sure use some help.
By the way, jumping the ALDL only gives a 12 code and running a steady flash off and on. I thought that meant not lean and not rich when the flash on time and the flash off time were about the same.