Looking for wiring diagram for 1986 pontiac with carb .when i look into the michell program it shows with ecm and injectors ???

Unless you buy a Clymer manual, free wiring diagrams are supplied in sections. In my search query add the name of the section you are looking for,

2008 pontiac g6 injectors wiring diagram

'cam sensor wiring' etc.

https://www.google.com/search?q=2008+pontiac+g6+wiring+diagram

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Find where the ground wire for that left taillight grounds to the body remove the screw and clean that ground, otherwise if the taillight assembly uses a printed circuit could be a break in the printing, replace the whole assembly if thats whats going on.

Did you clear the codes? Car may still be in limp mode...
Also the 303 is odd. Are the sparks good on #3? May have an issue with coil or ignition module.

That wire from injector to ecm is the grounding side of the circuit. The computer grounds the circuit inside when it is time for the injector to open. Not sure but I think all three wires on pass. side splice into a single wire going to the ecm. Check the continuity of the wires from pass, side to ecm. Any corrosion on the ecm pins?
Am I understanding right that you have power to both banks of injectors, but only one side, or bank, is firing? If it's not a wiring problem, it could be the computer.

Its BOTH, sort of....TBI Throttle Body Injection. If you look into the carb with engine running, you will see the injector spraying fuel onto the butterfly.

Actually the injectors don't spray "all the time". They pulse open for a few milliseconds then close every time they are grounded by the ECM. The distributor has a pick-up coil (Variable Reluctance sensor) that provides an A/C (Alternating Current) pulse every 120 degrees of crankshaft revolution to the Ignition Control Module also contained inside the distributor. The I.C.M. amplifies, rectifies and passes along the pules as a +12V square wave to the ECM. The ECM uses these pulses to calculate RPM and determine when the engine is rotating vs. stopped. Together with this information and more from Coolant Temp., Throttle Position, Manifold Pressure and Air Temp. the computer constantly 'looks up' what the appropriate amount of time it should pulse the injectors for to deliver the required amount of fuel.
With that in mind, the injectors are supplied with +12V via a 3 AMP fuse labeled INJ 1 for 1 bank of 3 injectors, and INJ 2 for the 2nd bank of injectors. Make sure your injectors are getting +12V whenever the key is ON or they wont fire (or at least 3 won't).
If all 6 injectors have +12V and you have fuel pressure (checked by pushing down in the center of the Schrader (tire valve stem looking thing) valve and fuel SPRAYING out, and your still not getting fuel it is probably because the injectors aren't pulsing. They are probably not pulsing because the ECM is not receiving any reference pulses from the distributor. If you have spark then you are producing reference pulses.
I hope some of this explained from an actual '86 Fiero GT 2.8L V6 owner/mechanic will help narrow down your problem.

ecm does control but is also based on input from the Throttle position senser. unplug the TPS and try again. Also make sure the ECM and engine grounds are good

The idle air control valve may be at fault, also the throttle position sensor may be telling the engine th wrong information and sending too much fuel, a couple other ideas come to mind but I not an expert. A faulty injector is one of them.....I another idea that may help as well: Vacuum Leak: The ECM will try to compensate for leaks up to a certain size. This will cause the ECM to compensate and possible send too much fuel to the engine...???? Good Luck

The ECM (Engine Control Module) could have been damaged when the battery was connected backwards. I agree with what lymand855 said as well but your problems could be worse if the ECM is damaged.

Did you change the spark plug?? Your car (1993) has a distibutor assy, which means it has ignition wires for each plug. How are your wires??cap?? rotor?? Have you ever done ignition tune up?? If the answer is yes and you have already installed new injector and pressure regulator (althoug it still could be a injection issue/ECM or computer, because ECM is what drives the injectors. If the ECM or wiring to #1 injector has an issue, the injector will not fire off and put gas into the cylinder, resulting in a misfire.) Remove #1 injector connector and check to see if you have power/12V on one side of the connector. If you have 12V there, than check the other wire for continuity to the ECM. You will need wiring diagram to find the right wire color at the ECM. That other wire goes into the ECM to the driver which opens and closes the injector depending on your demands as far as gas pedal input. That driver may be bad, causing the injector not to shoot gasoline. Than I would be looking into a engine issue, such as burned valve, or head gasket problem (coolant getting into #1 cylinder, flooding your spark plug). Tough to diagnose over the computer and not looking at it my self. Let me know what you find.