Should the solenoid have increasing voltage across the main terminals, 9.0vdc to 30vdc. Master switch in tow, key switch off.

Do yourself a favor an have it towed to a qualified repair shop. You probably have no idea how this vehicles systems work . When you turn the key to start , the ignition switch is not directly connected to the starter solenoid .This vehicles ignition switch is a low voltage input to the BCM - body control module , the BCM sends a message over the GMLAN serial data network to the PCM - powertrain control module to start the engine . Any number of thing's can interupt that message causing a no start condition. The BCM - is what is called the PMM - power mode master , when it see's any input from the ignition switch - off / ACC/ run crank etc... it sets the power mode . It will energize relays turning thing's on or off . Welcome to the world of electronics .
Circuit Description
When the ignition switch is turned to the Start position, the body control module (BCM) receives battery voltage on the ignition 1 voltage circuit, and less than 5 volts on the off/run/crank voltage circuit. The BCM supplies voltage to energize the RUN/CRANK Relay 32. The BCM sends a high speed GMLAN serial data message to the engine control module (ECM) that the key is in the start position. The ECM receives the message from the BCM, and also receives a serial data message from the transmission control module (TCM) containing the shift lever position. If the shift lever is in Park or Neutral when ignition switch is turned to Start, the ECM supplies voltage to the START Relay 31. The START relay supplies voltage to the S terminal of the starter solenoid, through the 30 A STRTR Fuse 26, in order to crank the engine.

Power to many of this vehicle's circuits are controlled by the module that is designated the power mode master (PMM). This vehicle's PMM is the body control module (BCM). The PMM controls which power mode (Run, Accessory, Crank, Retained Accessory Power, or Off) is active.
Serial Data Power Mode Master
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle, the PMM is the body control module (BCM). The PMM receives 3 discrete ignition switch signals to differentiate which power mode will be sent over the Serial Data circuits. The 3-wire Ignition Switch table below illustrates the state of these inputs in correspondence to the ignition switch position

There are a lot of possibilities. Bad starter relay, Bad ignition switch, bad starter solenoid, bad starter, anti theft engaged. First try hitting the starter while someone has the key in the start position.

Does not have a starter relay , When turning to key to start ,the ignition switch sends battery voltage through the park neutral safety switch ,for automatic transmissions or the clutch switch for manual trans . right to the starter solenoid . If you have a automatic trans try putting the gear selector into neutral . an see if it starts then . Have someone try an start it while you check for battery voltage at the starter solenoid S terminal . If it has Battery voltage at the S terminal ,voltage drop test the main B+ cable to the starter .
Starter Voltage Drop

Free wiring diagrams here http://www.bbbind.com/free-tsb Enter vehicle info. Year , make , model . Under system click on engine , then under subsystem click on starting . Click the search button then the blue link.

Use the wiring diagram to trace power from the battery.
it can be the ignition switch, security system, neutral safety switch, relay, or wiring.

Click no start is typically a bad battery, bad starter, bad solenoid or loose dirty battery connections. But seems you have covered those items. Have you checked you negative battery cable where it attaches to the frame and motor? Use multi meter and check from positive of battery to the motor(block) for 12 volts. Also do this while turning key to start position. If voltage drops out when doing this double check battery voltage and all connections. If it does not drop then check the solenoid wire coming from ignition. When key in start position you should have a good twelve volts. If you you do then test the main leads hooked to solenoid for power. If solenoid wire from ignition has less than 12 volts double check connections at battery and also test the clutch pedal switch.

Hello Lynn,

Sounds like you have a problem on the key controlled side, so:

1. Power from the battery to the key switch? 6V or 12V I would guess.
2. With the key in the "Start" position, have you got voltage to the thin wire/small terminal on the solenoid?
3. Do you have a good ground from the starter motor to the chassis?
If all the above checks out then the control circuit for the starter should all be working A-OK & when you turn the key to the "Start" position you should be getting a good, strong "Click" from the solenoid.

So - on the starter circuit:

1. The HD cable feeding the solenoid should always have battery voltage on it?
2. When you operate the key you should hear the solenoid "Click" and the voltage from the HD feed cable should now be connected to the other HD terminal on the solenoid (these are the two you are shorting out with your screw driver to get the motor to turn the engine over).
3. If the solenoid is "Clicking" when you operate the key & the voltage from the main supply cable is being passed to the second HD terminal, but the motor is not operating, then you need to check your ground cable.

Hopefully by now you will have found & fixed the problem :)

Disconnecting the leads from the solenoid,avtivating the switch, and reading 12V is normal because you are not reading anything but the signal applied to the solenoid.You need to attach the leads and THEN activate the switch and read the voltage across the terminals.12V would mean the solenoid is good because a voltage reading is a DIFFERENCE of electrical potential.If you have the leads attached and read 0V,there is no difference of electrical potential meaning there is actually 12V on both sides and the solenoid is not absorbing/using the power like it should be.If you simply read the 2 terminals on your battery it would read 12V,likely higher because a good battery will usually read close to 13V.A bad battery may read as high as 11.8V.As for the guages,it may also be that the battery is low if it has never been changed.The average life of an alkaline car battery is about 6 years.If yours was made and sold in 2000 like they like to do these days,the battery may have been changed once and is starting to be borderline.With the car off,no keys,nothing,read across your battery terminals and please let me know what you find. gmccarthy 86 hotmail
Greg

Check the voltage at the control terminal on the starter solenoid when you turn the ignition switch to start position. If you don't get anything, it's the ignition switch, a fuse or fusible link in the ignition circuit, or an open cable from the battery to the starter. If you get low or erratic voltage readings, check the battery terminal on the solenoid to see if you have the same readings. If you do, check the battery cable for corrosion or poor connections at each end. If you have full voltage there, the solenoid is bad.

If you get full voltage at the starter motor terminal, then the motor probably has bad brushes or commutator damage.

Do you hear a 'click' when the key is turned to start? Have someone try the key while you listen under the hood. It should be the starter solenoid clicking. You need either a test light or voltmeter to test further. One large terminal on the solenoid has the large wire from the battery positive, and should always show voltage/light at all times. Test the other side of the solenoid (large terminal) that is connected to the terminal on the starter motor. It should show light/voltage when the key is turned. If it doesn't, the solenoid must be replaced. If it does show light/voltage, then the starter motor is defective (probably brushes). If you get no click when turning the key, test the small terminal on the solenoid, you should see a voltage/light change when the key is turned. If you see a change, but no click, the solenoid coil is open or the case of the solenoid is not grounding where it is mounted. Try loosening the mounting and re-tighten. If no help, replace the solenoid. If you see no change at the small terminal, remove the wire from it and using a spare piece of wire, touch the small terminal to, first, the large terminal that the battery is connected to, then to the the mounting bolt for the solenoid. If the solenoid is good, the starter should operate with one of these two tests. In that case, the starter position of key switch is open--replace the ignition switch.

That wire may be coming from a relay so you may need a service manual to find which one it is.
BTW, to save frying all of your screwdrivers, applying 12 volts for a moment to the terminal with the smaller gauge wire will cause the solenoid to operate as it was designed. Shorting across the main solenoid terminals lets ~ 100-200 amps flow through your screwdriver which isn't even a very good conductor.
Even a light clip lead to the coil terminal of the solenoid could handle the lower current that flows there.
For purposes of doing several different engine tasks, I made up a momentary pushbutton switch contraption housed in a plastic film canister, put 6' wires and heavy clips on it so I could 'jiggle' an engine into the next cycle.