Need to know which is the a and b side of the ignition module on the distributor for a 90 GMC sub.2500

NO VIN told so>?
C2500 or K2500, Sierra is trim.
a PICKUP truck>?
Not a Suburban right?

most cars made have starter relay so the super expensive ignition switch does not burn up ST contacts.
and cars GAS have ignition module, only location changes (if a Distributor it's there) if not Dizzy it's in the ECU or on some cars fire wall to COP coils.
1991 C2500 guess a Pickup is it?
4.3L engine, sorry not doing all 5 engines and diesel
shows distributor and ICM and 1 coil.
and no relay starter see schem.



try here>?
https://eautorepair.net/Marketing/Default.asp

4.3L

What engine does yours have ? 4.3 - 5.0 - 5.7 L An just to get this straight , The ICM high voltage module is ? If you would like help you need to get your terminology correct !
ignition control driver (ICD) module. ,no high voltage module !
The enhanced ignition system used on all OBD II engines somewhat resembles the current distributor ignition (DI) system described in the ignition systems. However, the system has been greatly enhanced in order to make it compatible with the new OBD II regulations. The enhanced ignition system provides a spark at precisely the correct time in order to ignite the air and fuel mixture for optimum performance and fuel economy. The system consists of the following components:
?€¢
Vehicle control module (VCM)

?€¢
Distributor

?€¢
Ignition coil driver module

?€¢
Ignition coil

?€¢
Crankshaft position (CKP) sensor

Ignition Control Module
Top RH side of engine
Engine Controls Component Views
Engine Controls Connector End Views
Ignition Coil
Top RH of engine.

don't worry about it, MOVE ON, replace the EGR VALVE, have you replaced both the air & fuel filters ? do it. make sure plug wires donot touch each other !!! do you have an ignition module in your distributor, if so replace it, be sure to apply silicone grease underneath where the module mounts, on distributor base, not the module. helps prevent overheating of module . replace your OXYGEN sensor, do it ! see how all this works, good luck !

CONTROL MODULE-IGNITION

1992 GMC Truck C1500 1/2ton Sub 2WD 5.7L TBI 8cyl

The Control Module-Ignition is located: Under hood, center, rear engine area, mounted in distributor

Remove the distributor cap while cranking, see if the rotor turn. If not then the distributor gear is worn (need to replace the gear).
The ignition module could defect. Need to check the ignition module for power and ground and a bypass signal at the module.

Hope it helps.

See if you have spark on at least two plug wires. If you do, but it is weak, you may just need a good tune up (plugs, wires, distributor cap, and distributor rotor). If you don't have spark or it is only on one wire, take the distributor cap off and see if the distributor is turning while someone turns the key. If it doesn't spin, you need a distributor because the bottom gear is broken or stripped. If it does spin, then it could be the coil, ignition module, crank sensor, fuse or wiring to any of these parts. It will take a lot of wire testing and diagnostics to figure out which part it is if it isn't just a simple tune up or distributor.
Hope this helps. Good luck!

It is inside the Distributor, under the Rotor.

The distributor cap and/or the ignition rotor most likely have a crack somewhere and the distributor cap should be replaced along with the ignition rotor. The ignition module could have been damaged as well as the ignition pick-up coil/stator and if replacing the distributor cap and ignition rotor does not solve the problem then the ignition module or the pick-up coil/stator assembly inside of the distributor is also most likely damaged and the distributor will need to be replaced. There is a certain procedure for removing and replacing the distributor, and the ignition timing is not adjustable and it is not set using a timing light or with the engine running, and if you do have to replace the distributor Let me know if you require the procedure to properly remove and replace the distributor or if you require any further assistance.

'56 engine was likely a "blue flame" engine that had a points type ignition system. If someone installed a HEI setup in there, you need to know what year vehicle it came from. The old system used a hot wire from the ignition switch to the (+) side of an external coil...the (-) lead went to the points. The most common conversion uses the same (+) wire but it then connects to the "batt" terminal on the distributor cap.(coil is inside) There are no other wires involved except for the short harness that goes directly into the distributor that connects the coil, pickup coil and control module to each other..

Have you checked the coil