01 4.3L won't turn over

I'm working on my son-in-laws 01 S10 4.3L Automatic. The truck was over heating. I had to replace the intake manifold gaskets. Of course you know what all that involves. After replacing the gaskets and put everything back together, the truck will not turn over, it was running before. All we hear is a click under the dash when the key is turned. I've checked the battery, it has plenty of volts. Any help would be appreciated.

There are several items involved in the starting circuit: Battery connections; IGN C fuse, 20A, in the underhood panel (UEC); CRANK fuse, 10A, in the UEC; Park/Neutral switch; IGN A fuse, 40A, in the UEC; Ignition switch; Starter solenoid.

This might be helpful:

http://www.wwdsltd.com/files/2003S10StartCircuit.jpg

Check your grounds. A bad/poor ground can cause this exactly. I actually just diagnosed the same thing on an Eclipse my brother just picked up. After we got it home we took the known shot battery out and put a good battery in and it just went click. Thinking maybe something happened to the battery in the week since it was last checked tried jumping it and it still fought us to start.

Got it in a garage yesterday and threw a new ground cable on it and it fired right up with zero issue.

Ok, thanks. I'll check all this out on my next day off. I'll let you know what I find.

Ok, finally had a chance to check a few things out. I pulled the starter and had it checked. It was good. Although the connector on the PPL wire broke, I replaced it. I used an OHM meter and checked the grounds and they checked out good. So did all the fuses. The battery is steady holding 12.4 volts. The only other things i have not checked is the P/N safety switch and the IGN switch. I guess i could replace these and hope for the best.

Ok, finally had a chance to check a few things out. I pulled the starter and had it checked. It was good. Although the connector on the PPL wire broke, I replaced it. I used an OHM meter and checked the grounds and they checked out good. So did all the fuses. The battery is steady holding 12.4 volts. The only other things i have not checked is the P/N safety switch and the IGN switch. I guess i could replace these and hope for the best.

If you jumper the starter and it starts. That eliminates the neutral safety switch and the ignition switch.

When I jump the starter, the motor turns over, but doesn't start. When I turn the key to start, all I hear is a clicking under the dash, no fuel pump noise and no relays in the box are clicking.

Is the key in the on position when you try to jump the starter? If it is not then it isn't going to start.

I had someone turn the key on while I was jumping the starter, it would crank, but not start. It would just click under the dash.

So could it be either the neutral safety switch or the ignition switch? Or am I overlooking something else?

It could be any of the items in the schematic above, including the ignition switch and neutral safety switch. A voltmeter reading at various point along the path should quickly reveal the fault(s).

Ok, I'm not that great with electrical, but I did sleep at a Holiday Inn...lol. Anyway I got a good deal on an ignition switch, so I installed it to no avail. Still nothing. Using a test light, I have power to the 20amp ign c. fuse. When I use the test light on the 10amp crank fuse with the key off, no light, with the key on, light comes on and starter cranks. So I know there is power to the fuse. Next in line is the P/N safety switch. I have no clue how to test it. I did use the test light on the purple wire on the starter. With the key on or off or to the start position, it would not light up. I also noticed that 2 legs on the starter relay were hot.

So, any ideas?

Acquire a $10 utility voltmeter like this (https://www.harborfreight.com/7-function-digital-multimeter-90899.html) and begin taking measurements, right along the circuit as shown.

Well I've all but given up on this S10, until today. My neighbors truck broke down, so I went to help him. He's got a chevy V8. It was doing the same thing as the S10. Turn the key and just a click under the dash. Then I noticed that his security light was flashing. I used the remote lock and locked the doors a couple of times then unlocked it a couple of times. The truck started up. It got me to thinking could this be what's wrong with the S10. Of course there isn't a flashing security light, but could there be some kind of security issues with the S10? How would you get around it or disable it?

Is there 12V present at the 10A CRANK fuse in the Underhood Electrical Center (UEC) when the key is turned to the crank position?

I'll check it when I get home from work tomorrow and let you know

Okay, I haven't charged the battery in a while. It reading 10.1V. The 10 amp crank fuse is reading 9.5V when the key is turned to the start position.

So the CRANK fuse is getting whatever little battery voltage is available. That likely rules out the ignition switch and everything upstream of that.

The next place to test voltage is at the STARTER relay in the UEC. The contact for Pin 85 on that relay should get 12V when the key is turned to the crank position. If not, go backward to investigate the Park/Neutral switch on the side of the transmission.

Use care in disconnecting the plug for that switch. The factory used a melting sealant on that connector to help keep moisture and grit out of it. It helps to use a heat gun/hair dryer to warm the switch and connector up to about 150° to soften the sealant before disconnecting it.

Ive already replaced the neutral safety switch, wish I would have known about the sealant, it took a little effort getting the connectors off. I'll check the relay tomorrow and get back with you, thanks for the help.

I checked the relay, the bottom right, which I'm assuming is pin 85 shows 9.5V when the key is turned to the start position.

If the battery is fully charged that voltage should be much closer to 12. As long as there is battery voltage present that relay should be operating. If the relay is operating, the starter should operate.

Still working on it. No luck yet.