Chevy Tahoe Intermittent No Crank
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.