Truck won't start or crank

[juddspaintballs]

1999 Suburban 6.5L with 257,000 miles.

My wife drove it around starting and stopping the engine all day yesterday with no issues until later that evening when she went to leave the house again. She said it wouldn't start. I was at work and couldn't do much from there.

All dash lights and gauges work, DRL's turn on, lift pump cycles, glow plugs do their thing, etc. When the key is turned all the way to START, the DRL's cut out but nothing happens with the starter.

It won't start no matter what position the shift lever is in. It won't start while moving the shift lever either. It also won't start while moving the tilt wheel up and down.

Today, I checked things out thoroughly.

I physically checked ALL fuses in the fuse relay center and the fuse panel on the side of the dash. No issues. I tested the function of all relays in the fuse relay center. They all work. I disconnected all battery cables (which were clean and not corroded because I did this already a few months ago) and wire brushed the cable ends as well as the battery terminals and reassembled with some copper anti-seize. I pulled the starter off and bench tested it to be working properly with the solenoid. I tested the wires to the starter. The large power cable gets 12+v from the battery. The switched wire for the solenoid gets nothing.

I moved directly to the fuse relay center and pulled the starter relay. Although I checked it's function, I switched with another relay which didn't help. The relay is oriented in a manner that pin 30 is closer to the firewall and on the passenger's side, pin 86 is forward of pin 30, pin 87 is forward and on the driver's side, and pin 85 is toward the firewall and on the driver's side. The contact in the fuse relay center for pin 30 always gets 12+v. The contact for pin 86 get's 12+v when the key is in the RUN or START position. With the relay in, pin 85 receives 12+v when pin 86 also receives 12+v (whenever the key is on RUN or START). Pin 87 does nothing. I've now tried several relays, all of which test as working on a bench.

I can jump 12+v to where pin 87 sits in the fuse relay center and get the starter to crank. With the key in the ignition in RUN, the engine will crank but not start while I'm jumping 12+v to pin 87. Also, with no relay in the starter relay position, where pin 87 would be, I have continuity with ground on the battery.

I don't have a manual or wiring schematic so I'm not quite sure how that relay is supposed to work. I have a decent understanding of it, I think, and I would think that jumping 12+v to pin 87 would allow the motor to start if the starter is spinning the motor and I have no fuel delivery issues (I get a steady stream of fuel out of the bleeder if I open it up and the lift pump is running.

I have no idea where to investigate now. I don't know if this relay could be a potential issue or if it's working as it should.

Any help?

[FloridaHorseman]

Find the fusable link in the purple starter solenoid wire, splice around it and see if it'll crank. ~FH

[FloridaHorseman]

Oooops.... if you get starter crank jumping 12v to pin 87 the fusible link should be OK. Next guess would be the neutral safety switch has failed.

One more guess... when the key is turned on does the SECURITY light in the upper right corner of the dash panel stay lit or go out? ~FH

[juddspaintballs]

The security light goes out. I forgot to mention that but I am aware that can be a problem.

[racer55]

You found the answer when you said pin 85 gets 12v when pin 86 gets 12v.
Pin 85 should be ground to complete the circuit in the relay for the winding that creates the magnetism to close the contacts between pin 30 and 87.

Repair the bad ground at pin 85,it doesn't have to be fancy,just splice a new ground into the wire that terminates in the relay socket pin 85.

Picture in this thread should be similar to what you have and might illustrate things a bit better,reverse what I put in that post for pins 85,86:
Still Problems Starting Please Help !!

[racer55]

Another way to put this would be:
Pin 85-ground
pin 86-power when key in start(should not be power there with key in run)
pin 87-power to starter solenoid
pin 30-constant power

[juddspaintballs]

I thought that I needed a constant ground on either pin 85 or 86 but I was unsure if GM was going for a ground switched starter or a positive switched starter. So if 85 is getting 12v when the key is turned, that means the ground on 85 is bad? For the sake of testing that theory, could I wrap a wire around pin 85 of the relay, stuff it back into the fuse relay center and ground that wire to the battery to see if that solves the problem?

If that doesn't work out for me, I was thinking possibly the neutral safety switch as well. If I unplug the switch, which two pins do I need to jump to fake that I'm in P or N? I had to do this on my Blazer when I switched it from an auto to a manual (I did wire that loop into the clutch switch), but I only figured those wires out by trial and error and several blown fuses.

[racer55]

First plan is the best 1 if the wire and relay will fit back in place.
Not sure which wires need jumped-manual is in the shop.

[juddspaintballs]

I grounded pin 85 to the battery and stuck the relay back in. As soon as I turn the ignition switch to RUN it begins cranking but won't start. I'm thinking it's the ignition switch at this point so I'm ordering one right now.

Any other thoughts?

[racer55]

Sounds like the switch or wires melted together in the column or firewall.