[Gmecm] How to wire Timing Bypass on 4-Cyl 151 Iron Duke?

[Aphelion79]

Hey, remember me? The newbie with the 4-Cyl 151 Iron Duke and the CJ7?
Well anyway, I'm finally able to start working on my Heep again... and 
am curious as to how to set the timing on this thing...

Now, all vehicles have some sort of timing advance... on carburated 
engines (just spilling out how I understand it... correct me if I'm 
wrong with anything) you unplug the vacuum advance hose and plug the 
port as to not cause any vacuum leaks... and set the timing... on a 
TBI'ed vehicle... there is a special wire that has an in-line coupler 
that allows you do disconnect the signal sent to the Distributor for the 
electronic advance... unplug that, set timing.. yadda yadda

But here's my problem:
On a 88 Chevy S-10 Pickup, "there is a black/red wire under the 
passenger's side floorboard that you can disconnect and then set the 
timing"... well... I obviously do NOT have an S-10... nor any wires 
inside of the firewall as I just spliced most of the wires off that went 
to the fusebox... and I've followed diagrams of the ECU pins and could 
not find any mention of this special wire... However... on GM-ECM I 
found a schematic for the 7747 ECM 
<ftp://ftp.diy-efi.org/pub/gmecm/manuals/1227747/747ecm6.jpg>
(ftp://ftp.diy-efi.org/pub/gmecm/manuals/1227747/747ecm6.jpg) -which is 
NOT the ECM I have... (if this information is current, got this from an 
old post I made a while back on a different forum:) mine is:

SVC# 16198445
Barcode:
866647W643273117
Chip Inside:
ACKD 4890

The previous link to the 7747 indicates the TAN/BLK wire right off the 
distributor controls the timing bypass... now I've disassembled my 
wonderfuly sexy wiring loom and traced all 4 wires that come off of the 
distributor...and each one of them goes DIRECTLY into the ECM... none 
have any splices in them as well or any disconnects in-line... Would 
splicing into the wire, and creating my own quick connect/disconnect 
in-line plug right at the 4-pin connector off the distributor be a good 
way to do this or am I missing something? I could simply "just try it" 
but I wanted to run this by you all first... you guys seem to know more 
about this stuff than any of us on JeepForum

Thanks again... !! By the way... the Jeep runs... haven't started it up 
in 2 months and it fired right up... however it idles a bit rough and 
doesn't have very much power at all... so I figured timing would be the 
issue! I previously set the timing by luck by putting it at top dead 
center... unplugging the whole entire 4 pin connector off of the 
distributor -which doesn't allow the engine to run- and had a helper 
eyeball it to 0* and plugged it back in...

Anyway, enough length on this... any other questions or things I should 
look at let me know!