Starter won't dis-engage when key is turned off.

[80sGuy]

I'm an idiot, so please don't judge. I need help with this issue please: '86 GMC 3/4 ton Sierra Classic Camper Special with the side terminal battery. Cable connections were tight but all I got was a 'click' when I turned the key to start. Ended up cutting a bunch-o-plastic away from the negative terminal so now I got good juice. BUT, thinking it was the key switch, I replaced the lock cylinder. Got [discouraged] when I finished that job and all I still got was the 'click' when I tried to start it. Okay....must be the starter. Replaced the starter. Well, all I got was the same 'çlick'. That's when I cut away the plastic from the negative battery terminal.
So it started fine for a couple of weeks, but I noticed on a few starts, it seemed the starter drive would hang up ever so briefly. May need a shim, i thought, but I'll get to it later. Well, three weeks later in the parking lot at our local big box store, I started the truck and the starter never dis-engaged. I could turn it to 'off' and even take the key out. I had to jump out and disconnect the battery to get it to shut off. Thought maybe an internal short in the solenoid, so O'Reilly gave me another starter. Same thing; it engages the solenoid, and whether the truck starts or doesn't start (like when it's cold), the starter drive doesn't dis-engage--even with the key off. Tried putting the old lock cylinder back in---same thing, starter wouldn't dis-engage. So I did put the new (Genuine GM) lock cylinder back in (basically did that job three times). Couple things to note: 1) It doesn't spin the starter by simply hooking the negative cable back up to the battery terminal; it appears to dis-engage the solenoid when I disconnect the neg terminal and will re-engage only by turning the key to 'start', and 2) It's somewhat erratic; I was able to get the truck home from the big box store because the starter started the truck and dis-engaged properly--at least that time. So now what? Not sure whether to address the starter or the key switch. I plan on going ahead and putting a shim in, but I don't know what I could or should be looking at on the wiring while I'm under there. I question whether I did something wrong when installing the lock cylinder. A parts diagram would help, and btw this steering wheel hub has an electrical piece with two prongs that I've never seen in any square-box videos. Also, not sure what is supposed to be powered-on at the Acc position, and the 1st position on the up-side of the lock position (with 'on' and 'start' being 4th and 5th positions). Truck is all original except some owner many years ago before me somehow killed the buzzer. I've had it 21 years and have never had a problem like this. Sorry to be long-winded, but I'm trying to give as much info as possible. Any help is appreciated. Thanks in advance. -Alan

 

[Ricko1966]

Check battery condition,cables and battery grounds. 1 to engine 1 to body 1 to frame. Sounds like voltage/amperage problem battery, cables,yes they will cause the starter to stay stay engaged or not engage. What happens is when you decrease voltage you increase amperage,it's ohms law. The increased amperage sticks the points in the starter solenoid.

 

[edgephoto]

You said you replaced the lock cylinder. I would look at your ignition switch adjustment before I did anything else. The switch is at the base of the column.

If it cranks with the lock cylinder in the off position you either have power engaging the solenoid or the contacts in the solenoid are stuck closed. Since you already replaced the starter a second time, I doubt it is the solenoid sticking.

@Ricko1966 Not looking for an argument but if voltage goes down, so does current, given the resistance is the same. Volts=Amps x Ohms.

 

[Ricko1966]

You said you replaced the lock cylinder. I would look at your ignition switch adjustment before I did anything else. The switch is at the base of the column.

If it cranks with the lock cylinder in the off position you either have power engaging the solenoid or the contacts in the solenoid are stuck closed. Since you already replaced the starter a second time, I doubt it is the solenoid sticking.

@Ricko1966 Not looking for an argument but if voltage goes down, so does current, given the resistance is the same. Volts=Amps x Ohms.

I still see a possible voltage problem,that's causing the same problem with a second starter. Now if you look back in vehicle history,look at the gauge of the wiring in 6 volt cars,it was huge to carry the amperage of a 6 volt load,they switched to 12 volt and the gauge dropped substantially, they pump 120 volts to our house,we run compressors and air conditioners,etc,etc. None of the wires in our house are as big as the battery cable that provides power to the starter. Maybe I don't have ohms law remembered correctly,but I have seen plenty of starters that don't disengage, caused by low voltage conditions,I've also seen lots of starters click but not crank due to battery cables causing low volts,Ive never seen an ignition switch cause both those problems on the same vehicle. Anyways IDK I thought it was ohms law causing excessive amperage draw in low voltage situations. So what formula is watts÷volts=Amps? You can all try this at home 1000 watts divided by 12volts equals 83.33 amps, as you start decreasing the voltage the amps go up dramatically 1000 watts divided by 6 volts equals 166.6 amps. Anyway I've seen lots of starter problems caused by low voltage,I always thought it was ohms law.

 

[Jgonick]

power law (power formula)
Power = V X I

(watts = volts X amps)

 

[Jgonick]

Wiring diagram-LINK

Steering column-LINK

Also, not sure what is supposed to be powered-on at the Acc position

radio and wipers