86 K20 No start, bat & starter good

[Lotus907]

Good morning all:
I have a 1986 K20 that the previous owner added a 454 w/TBI from a 1987 Suburban R20 and I have been experiencing some issues with getting the truck to start. Recently I have had occasions where the starter is not being activated when I turn the key. Previously when this has happened I goof around with trying to turn the key off and on a few times and then finally it will work. However last evening when I wen to use the truck after two days of sitting this happened again and no amount of fiddling with the key did anything. I tried jumping the battery since it is very cold here but that had no effect. I pulled the battery, brought it in the house to check it and it seemed fully charged.

The lights on the dash are lighting up as normal when I turn the key to On or start positions and I can feel resistance when I turn the key to the start position. Just nothing happens with the starter.

I believe I either have a problem with the neutral safety switch or the ignition switch. I understand from the research I have done that the actual electrical part of the ignition switch sits on top of the steering column and is activated by an ignition activator rack. However I have no idea where the neutral safety switch is located.

BTW, the truck does have a tilt steering wheel.

So now I have questions. 

1. How do I diagnose if it is indeed the neutral safety switch or the ignition switch.

2. Where is the neutral safety switch located?

3. Is it possible to drop the steering column enough to access the ignition switch by just removing the two large nuts under the leading edge of the dash that hold the column up in place?

4. Where can I get a good wiring diagram for a 1986 K20 and a 1987 R20?

One other piece of info, it's 15°F outside so I am trying to minimize the amount of time I am lying under the truck if possible

 

[RThiel]

#1 - Jumper the wires together and see if it starts - purple wires

#2 - at the base of the steering column. It also includes reverse lights - two green wires.

#3 - yes

#4 - I think there's one on this site somewhere, but I can't remember

Crawl up under your brake pedal and find the switch at the bottom of the column. pull the purple wires off and jumper them together, hit the key, and see if that's your problem. If not, drop the column down, the ign. switch is actuated by a rod from the lock cylinder and can be adjusted by loosening the switch and sliding it.

 

[Lotus907]

Neutral safety switch wiring

Thanks a bunch for your reply.
However I do not see any purple wires.

#1 - Jumper the wires together and see if it starts - purple wires

#2 - at the base of the steering column. It also includes reverse lights - two green wires.

#3 - yes

#4 - I think there's one on this site somewhere, but I can't remember

Crawl up under your brake pedal and find the switch at the bottom of the column. pull the purple wires off and jumper them together, hit the key, and see if that's your problem. If not, drop the column down, the ign. switch is actuated by a rod from the lock cylinder and can be adjusted by loosening the switch and sliding it.

The neutral safety switch seems to be coming apart as there were loose pieces hanging.

Here is the wiring I see on the pieces of the neutral safety switch that I found in the truck. One plug with a red wired and a black w/white wire. A second plug with a green wire and a blue wire.

See the attached drawing of these connections.

 

[Lotus907]

Pics of piece I pulled out

Here are a couple of pictures of the piece of the neutral safety switch that sort of fell out of the truck. It was mounted on the top of the steering column. It was only hanging on by a small piece of the original plastic housing. Obviously there is still the other half of this switch assembly still attached to the column. I have not yet figured out how to remove that other part yet. Do I have to drop the column to change this?

 

[RThiel]

I'd say that's your problem. I'm pretty sure if you jump the red and black w/ white wires, it should start. If not, your reverse lights will be on, and then you'll want to jump the blue and green to start it. Lol! I'm pretty sure it's the stacked connectors on the left anyway. Usually they're both purple, because one of them goes to the S terminal of the starter.

 

[Lotus907]

I just checked the four wires with a trouble light. Just the blue wire lights up when the key is switched to On. None of the wires get power when the key is turned to the Start position. I.E. neither the red or black w/white or the green wires do anything at all as far as having 12V power appearing when the key is turned to the On or Start position. My guess is from what you have said the blue wire is indeed for the reverse lights. So to me that sounds like I also have an issue with the ignition switch.

I am going to try jumping power to the black w/white wire to see if the starter does engage.

 

[Lotus907]

Well, that didn't work. When I jumped 12V power from the blue wire to the black w/white wire with the key in the On position, I managed to immediately blow the 15A fuse for the reverse lights. Is it possible that there is a starter relay in the system and these column wires through the neutral safety switch are just to trigger a starter relay?

BTW, the idiot GM engineer who decided the damn fuse box should be buried WAY up under the dash should just be taken out and shot!

 

[Lotus907]

Found a wiring diagram for a 1987 series of trucks which would sort of match up with the 454cid w/TBI engine that is in my truck and it seems the red wire is actually orange with a black stripe and it goes to the ECM labeled "Park/Neutral In". The black with white stripe seems to be a ground. I see the purple wire on the diagram going from the ignition switch to the starter but these wiring diagrams are difficult to understand so I cannot tell if it goes someplace else as well. I.E. I cannot tell if there is some intermediate location or connection between the the ignition switch and the starter. I see the purple wire going into big wiring plug that passes through the firewall (one plug on the interior of the truck and another plug on the engine compartment side of the firewall).

So I am not really understanding how having the neutral safety switch wired into the ECM stops the starter from working in anything other than park and neutral. I do not see any other connections to the ECM that would seem to have any effect on the solenoid on the starter engaging or not.

/color me confused.

 

[RThiel]

The only starter relay is right there on the starter. The battery terminal goes to the large lug, a fusible link that supplies power to the rest of the truck comes off the same lug. The S terminal power comes from the ignition switch in the crank position, interrupted only by the neutral safety switch, to power the relay and make the contacts close. I can't see why an ECM would interact with the cranking circuit unless it needs that info to allow the ignition to energize. I can't say that I've messed with an '87, though your original post says your truck is an '86. At this point I would have to start chasing out the wiring myself, checking for power along the way.

 

[Lotus907]

OK, I tried jumping power from the positive battery cable lug on the starter to the S terminal and nothing happened so I decided to pull the starter. Once I got it out it sounds weak when I try to jump it off of the actual battery but then just for grins I had a friend come over and turn the key while I checked under the car for power on the wire going to the S terminal on the starter. Nothing! No power on that wire that connects to the S terminal on the starter when the key is turned to the start position on the column. Back to the drawing board.

 

[Lotus907]

There is a fuse down at the bottom of the fuse block that is supposed to be a 3A fuse and it is labeled on the fuse block "CRANK" What does this fuse do? One of the wires going to one side of this fuse goes to the ECM to a terminal labeled 'CRANK IN" and the other wire is a purple wire that ties into the purple wire going to the S terminal on the starter from the ignition switch.

This info is according to the wiring diagram I have for the 1987 trucks.

 

[RThiel]

It sounds like you have a problem with battery terminals or cables if you can't even get it to crank by jumping the starter directly. I would imagine that the crank fuse maybe sends momentary voltage to the ECM (that's why only 3 amps) for whatever reason. Take the starter to a parts store and have it bench tested. Have your battery load tested too. The starter should have enough torque sitting on the bench to try and roll if you don't hang on to it. You should be able to trace power from your starter to your fuse box, to the ignition switch. After the ignition switch it will split. One wire will supply voltage to the ignition, another will only have power in the "crank" position (as opposed to "run" position) to the neutral safety switch, and to the starter S terminal, so you're gonna need that friend to hold it for ya, while you run through it with a test light.

 

[HotRodPC]

Did you blow the fusible link on the firewall when you crossed something and blew the reverse light fuse?

Can you use a screwdriver and cross the positive to the solenoid? That should bypass everything and at least crank. If it won't start, it's due to the fusible link being blown or the key is not in on position. How about all your accessories in the cab? Are they working? If not, then you can be pretty sure you blew the fusible link also.

 

[chengny]

Found a wiring diagram for a 1987 series of trucks which would sort of match up with the 454cid w/TBI engine that is in my truck and it seems the red wire is actually orange with a black stripe and it goes to the ECM labeled "Park/Neutral In". The black with white stripe seems to be a ground. I see the purple wire on the diagram going from the ignition switch to the starter but these wiring diagrams are difficult to understand so I cannot tell if it goes someplace else as well. I.E. I cannot tell if there is some intermediate location or connection between the the ignition switch and the starter. I see the purple wire going into big wiring plug that passes through the firewall (one plug on the interior of the truck and another plug on the engine compartment side of the firewall).

So I am not really understanding how having the neutral safety switch wired into the ECM stops the starter from working in anything other than park and neutral. I do not see any other connections to the ECM that would seem to have any effect on the solenoid on the starter engaging or not.

/color me confused.

The P/N switch is used to provide the ECM with an input signal for control of the IAC (idle air control) valve, EGR valve and is somehow related to the VSS (vehicle speed sensor):

You must be registered for see images attach

For example, the IAC valve is commanded "open" to a greater degree when the transmission (automatic only) is in any gear other than P/N. This maintains the proper idle speed in spite of the increased load due to the engaged drivetrain.

Also, in AT applications, power from the ignition switch (to the solenoid
"S" terminal) is not switched at any point - other than at the ignition switch. The purple lead is run directly from the switch through the firewall and down to the solenoid. The NSS was phased out well before 1986 - it was replaced with a mechanical interlock located in the upper portion portion of the steering column. If equipped with a MT, power to the solenoid is switched at the CSS (clutch safety switch). The lead also changes from yellow to purple at the CSS.

The statement below would seem to indicate that either:


1. The ignition switch is out of adjustment/failing, or

2. There is a tenuous wiring connection in that circuit.

Previously when this has happened I goof around with trying to turn the key off and on a few times and then finally it will work.

The steps to access/R&R the ignition switch are explained here:

http://www.gmsquarebody.com/forum/showthread.php?t=16237&highlight=ignition


It is likely that the combination NSS/Backup light switch was installed when the truck was converted to TBI from a carbureted system.

Bottom line, while it might cause poor idling (and the EGR system to malfunction), the lack of a P/N switch will not in anyway affect starter operation.

 

[chengny]

There is a fuse down at the bottom of the fuse block that is supposed to be a 3A fuse and it is labeled on the fuse block "CRANK" What does this fuse do? One of the wires going to one side of this fuse goes to the ECM to a terminal labeled 'CRANK IN" and the other wire is a purple wire that ties into the purple wire going to the S terminal on the starter from the ignition switch.


The purple control lead to the solenoid is branched off inside the cab. One leg goes to the "S" terminal as noted above. The other leg supplies power to the line side of the CRANK fuse. The load side of the fuse runs to pin C9 of the ECM and that input tells the control module that an attempt is being made to start the engine. The circuit (806) is immediately de-energized as soon as the ignition switch is released from the START position.

You must be registered for see images attach

And, as with the P/N switch, a loss of a signal from the CRANK fuse has nothing to do with starter operation. It might cause some occasional hard starting, but the engine will still crank over at full speed.

As an aside, the line (LH looking forward) side of the CRANK fuse would be a convenient place to begin ringing out the starter control circuit. If you see voltage there, you can eliminate the ignition switch as the issue. After that, you are essentially down to a break in the purple wire - between the splice/branch point and the "S" terminal.