2000 chev truck auto trans no start

Do you know what a wiring diagram is ? How to use a DMM - digital multi-meter to diagnose automotive electrical circuit's ? Looking at a wiring diagram to see what all is involved in the starter circuit , main battery cables , park neutral safety switch , starter relay etc.. Find video's on youtube . Do you have a manual or automatic trans. ? The purple wire get's B+ voltage from the starter relay in the underhood fuse / relay box .

How to voltage drop test starter motor circuit
When your car wont crank or start part 3 How to check relays fuses...

Well, looking at the schematic, there is the IGN A (Fuse 6) in the under-hood fuse block feeding power to both the ignition switch and to the NO contact of the starter relay. Turning the ignition switch to the START position sends this voltage thru the CRANK (Fuse 8) in the instrument panel fuse block and thru the PARK/NEUTRAL position switch, thru the starter relay coil to ground. This should activate the Starter relay and pass voltage to the starter solenoid to ground, activating it. One the starter solenoid activates, batter power is sent to the starter motor, activating it. If, as you say, the fuses are good, the starter relay was replaced and is good, and the Park/Neutral position switch was replaced and is good, then then only items left are the ignition switch itself, the starter solenoid/motor, or the wiring of the circuit.

This could be a couple different things causing your No-start condition. first thing I would check (Battery is good) access the starter solenoid, the small single wire connection is the start signal. Test for 12 volts here with DVOM or test light while someone turns the key. If there is 12 volts reading, the starter solenoid is defective. If there isn't 12 volts reading check all the fuses (with test light).
The second item causing the trouble could be the Neutral Safety Switch (Auto Trans) or Clutch Safety Switch (Manuel Trans) These could be open or out of adjustment.
Hope this helps you...

There is no starter relay shown in a wiring diagram. The only thing between the ignition switch and the starter solenoid is the park/neutral switch (or the clutch pedal position switch on manuals).

Do the warning lights and gauges come on with key on? That would verify power is into the switch and being sent out. The small purple wire on the starter solenoid should have power on it when the key is held in start position. If it does, recheck your starter and battery connections. When the purple wire energizes the solenoid, the starter motor should crank the engine.
If no power on the purple wire in start, check the neutral safety switch or the clutch switch if a manual. The start wire out of the ignition switch is a yellow wire, and the wire from either safety switch to the starter solenoid is a purple wire.
(The power to the ignition switch is from the 50 amp Ignition fuse in the under hood fuse block.) See? The positive battery cable is connected to the starter, but not to the starter motor. When the key is in start, the hot purple wire energizes the solenoid and the battery cable is connected to the starter motor.

From the ignition switch there is a yellow wire that is for the starter. probe it when trying to start. If you have no voltage replace the switch. Also, I believe there is a fusible link in the wire by the starter. It will be a different color than purple. Probe on the back side of it to see if there is voltage at start up. If so, replace with the smae color link.

I think the purple wire (or maybe the yellow) from the neutral safety switch goes to the coil side of the starter relay, turning it on so power is sent from there to the starter solenoid. You could check for this signal to the relay with a test light. The key must be held in start while you probe the other two terminals for the relay. If the signal is there, either a bad relay or the coil side of relay is not grounded properly. It is possible that the coil side ground is the neutral safety switch-grounding the relay's coil side only in park or neutral-in which case the nagging light on shifter (between off and run, it only works?) may be telling you the safety switch is the problem.

You may need to look at a wiring diagram, Greg. But the starter relay is the last component in the start circuit before the starter solenoid. From battery to ignition switch to "crank" fuse to neutral safety switch to starter relay to starter solenoid to starter-and back to battery through ground. That is the start circuit. Just that the wiring tying them all together makes it complicated.

I will try to help, powell. Your start circuit from battery to ignition switch to starter-and back to battery. You may need to check every thing here, including the grounds, for a loose connection, or just possibly a failing part.
If only complaint is intermittent starter action, and no other problems with ignition switch, let's assume switch is good, so battery to ignition switch is good. Now from the switch, a yellow start wire goes to the instrument panel fuse block, to "crank" fuse #8 (10 amp), from there a purple wire goes to the safety switch. If manual it is a clutch pedal position switch (simple on/off switch-when clutch down switch is on). If automatic, purple wire goes to Transmission Range Switch on the transm.-in park or neutral the purple wire has continuity in and out of switch.
From that switch, the purple wire goes to the starter relay (under hood fuse-relay center). Now the relay: purple wire in start will energize the relay- wire goes to coil side of relay, and then coil side goes to ground. On relay power side, the power feed is a red wire-and it is the same red wire that initially sends power to the ignition switch. A 40 amp fuse in fuse-relay center sends power to ignition switch, and a splice goes to the starter relay as the power feed for relay. When relay is energized, contacts close, and power is sent from relay to the starter solenoid, again on a purple wire. When solenoid contacts close, starter motor is connected to the big battery cable on the starter.

There is your start circuit. try a new or different relay, try a new or test the clutch switch (or transm. range switch). Buy a $5 test light and use it to check where power is lost when starter won't operate. Hold key in start and check if fuse #8 is getting power. Check the safety switch, with key held in start, the purple wire should be hot. Check if relay has a power feed (pull relay out and check terminals) and if relay coil has a power signal in start. Check the relay's coil side ground. If that ground is intermittent, relay won't work.
When it won't start, use a test light, you should be able to find it.
Good luck.

Where is this relay? A wiring diagram doesn't show any relay at all in the starting circuit. Just this: a yellow start wire out of ignition switch goes to the neutral safety switch (if manual, a clutch start switch on the clutch pedal: if automatic a transmission range switch); From the safety switch a purple wire to the starter solenoid on the starter motor. Only other place to check is a "crank" fuse in the instrument panel fuse block- a 10 amp fuse in position 8 of the block.
Is the click you hear possibly from the starter solenoid? If it is, that means key switch part of circuit to the solenoid is good. Either starter motor is bad, or battery connections to starter and to battery ground may be bad, check them first.

Probably not a fuse. When turning the key to on, does it give indication of power in and power out of the ignition switch-do the warning lights and gauges on the dash turn on?
If the key switch is sending power, next thing to check is the starter motor. You could take it off and have it tested, it and the starter solenoid mounted on the starter, or you could do some quick electrical testing yourself, if you have a test light or multi-meter.

If you pull off the small purple wire to the starter solenoid on the starter, you should check if the wire has power when the key is held in crank position. If it does have power, the starter or solenoid is faulty. If no power on the purple wire in start, then power is lost between the key switch and the solenoid. This part of the start circuit includes the neutral safety switch on the transmission (or the clutch switch if manual transmission), and a starter relay somewhere under the hood. Check the neutral safety switch for continuity in park or neutral. The start wire out of the ignition switch goes to this safety switch, and power is passed on to the starter if gear is in park or neutral.
Not likely the starter relay is bad, but you may need to find and check it, if all else fails.

Could be the starter solenoid.
The key switch sends power to the solenoid thru the neutral safety switch. You would need to check for power on the purple wire at the solenoid when the key switch is in the start position.