Picked up this project car a month ago. Runs good did basic maintenance. Starts right up and idles smooth at 600. Normal SES on key on but off when started.

when I changed the oil SES light came on and would not go off at all. Paper clip for codes would not flash at all. Ground on C is good. Pulled the LDM, light off. Replaced LDM, now No SES light at all. Still starts and runs good.

fuses are all good.

side note: cooling fan relay was cut out by PO. Wired direct to a fuse jumper into fan fuse. Took that all apart, found the all wires and ordered a relay and pigtail. Put a new fuse in and choke light is on at key on but goes off proper on startup. Related? I dunno

 

I understand that this has probably been covered many times. I've searched and found some issues that may be close, but not quite. Or tried fixes recommended without any success. Not trying to waste anyone's time, but there is a lot of knowledge in the membership here.

 

I am going from my memory here, to get you some sort of answer quickly.
The choke light is actually also an ALT light. Therefore at key ON, the bulb should be on because the ALT is not charging.
Once you start the engine, and the ALT is now charging, the bulb goes out.

 

That makes sense, and I found a thread explaining that. So when I worked on that problem is when I found the hack job on the fan relay being cut out. So, that part of my question leads to... Does having the fan relay not being connected possibly causing any problems with the ECM not working or with the SES light issue. I think it would not. My problem now is really the check engine light was always on suddenly. replaced the lamp driver, now it won't come on at all.

 

Let's see here, you had the SES light, replaced the LDM and now no SES light whatsoever.
Either the lamp blew, the new LDM is no good, or the ECM is bad or disconnected.
I don't know if your fan is controlled by the ECM, but if it was, then that might be why the PO previous owner wired it directly to a fuse.
So you can't even get a code 12 to flash, correct.
Check to see if the ECM fuse is installed and not blown, see if the ECM is even plugged in.
You say it starts and runs good. Is the MCS in the carb ticking? It should even tick when you just turn the key to ON before starting.

 

Possibly the new ldm is no good. Or something happened with the ECM. It is connected and the fuse is good, verified with meter. The MCS ticks away at key on.

So I’ll get a wire diagram and check grounds and test continuity on wires to the ECM.

However, since it runs fine I may just ignore it for a while. Any concerns about that?

 

I could be wrong, but if your MCS is ticking, then your ECM is working.
Do you have a dwell meter? With the engine warmed up and in closed loop mode, connect it between ground and the middle wire of the MCS to see if the reading changes. I push common pins through the wire's insulation, and then clip the leads onto those. Make sure nothing shorts together or to ground.
There should be an unused connector by the heater box that the factory would use to check this. I just can't tell you exactly where it is, and if you even have it.
Maybe someone else could provide a pic.

If the dwell reading changes (should swing back-and-forth around 30 degrees), then the ECM is definitely working.

 

ALDL PIN 'C' should be a BROWN wire that retrieves ground from the ECM for the Air Select Valve. (SMOG)

Looks like you should be jumping ground to PIN 'D' (YELLOW wire) on the ALDL to test the CHECK ENGINE bulb; and checking that same terminal for ground from the Light Driver Module to test the Module


This is from an 85, but 86 should be similar: