HouseCallAuto 4/1/2010When it does not start you have to check for the 12 volt signal at the small wire going to the starter with a 12 volt test lamp when you crank the engine only. You mentioned several things replaced but not the starter? Or did you fail to put a comma after the word "starter" in your sentence? I'll assume that you DID in fact replace the starter. That leaves the aftermarket alarm if there is one that is, or the neutral safety switch. Please do the test light check and let me know. There is a starter motor relay in the power distribution center under the hood. Could be that. Try tapping on the relay when it does not start.
HouseCallAuto 4/1/2010Here is a diagnostic that is very specific if you can carry it out when the problem exists.>
The engine will not crank over.
Tests/Procedures: 1. Test the voltages at the starter relay. Terminal 85 should be grounded at the neutral safety switch on the Black/White wire.
2. Terminal 86 needs to have battery voltage when cranking. This comes from the ignition switch and clutch switch.
3. Terminal 30 should have battery voltage at all times, this comes from fuse 2 (40 amp) fuse in the Power Distribution Center (PDC).
4. Terminal 87 goes to the starter solenoid.
Potential Causes: Ignition Switch
Neutral Safety Switch