Hey everyone...have a 73 LT-4 Vette, auto, fully optioned. All O.E

She will not start...or even crank for that matter. All accesories still work. Starter is new, solenoid is new. Here is what I have done so far.

1. Checked battery. Was a little low on voltage so I had it load tested and fully charged. Attempted to jump the car with known good battery but still no cranking.

2. Checked and cleaned battery to frame ground, starter to block and block to motor mount grounds. Connections good and tight with no corrosion visible. Seeing full battery voltage at the battery terminal on starter solenoid.

3. With key in start position I see correct voltage up to the distributor. Only approx 8.2-8.4 V on the S terminal. It is enough to drive the solenoid and make contact with flywheel but not enough to spin starter. Have a pushbutton setup in the mail but have not installed yet. Tried to make a jumper here but its very tight and that's sort of sketchy underneath the car. My attempt did not allow the car to turn over.

4. With headlights on during start attempt they dim but do not go out and accessories go off as they should to allow max current to starter.

5. NSS shows battery voltage (12V) between purple and purple/white when key turned into start position. Jumper across switch has no effect on cranking.

Something is causing some unwanted resistance in this circuit. If I read the wiring diagram correctly purple/white runs from IS to NSS. NSS close the circuit when in park or neutral between Ppl and ppl/white wire. If I see 12V here then I believe the Ignition Switch is good. Is this correct?

Purple then runs to S terminal on solenoid. There is a fuseable link somewhere on there...but don't they normal conpletely fail? A jumper from purple on NSS to S terminal did not help so I used that to eliminate this wiring section.

Next step anyone????

 

Update: Tried a push button switch connected from starter solenoid to S terminal and the motor does not crank. The starter gear pushes forward and meshes with the flywheel properly. All electrical circuits check out so far. Took off battery box to ground and block to motor mount ground and cleaned all connecting points thoroughly. Both cables pass a continuity test.

 

Remove starter, with known good battery, jumper calbes, you're remote jumper switch, bench test the starter. If you have a motor draw test guage, the amperage draw of a freewheeling motor is under 35 amps. The starter solenoid; when the 'S' terminal is energized the coil becomes magnetized causing the bendix to be thrown outward to enguage with the flywheel, also internally inside the solenoid there are copper contacts, [one stationary, one rotary] that then allow the battery voltage to be connected to the motor itself causing it to rotate. This is a high known failure. The stationary post is worn and burnt [it can be removed, rotated, reinstalled]. If starter motor passes bench test, let us know we'll go onto step 2. T

 

You could have two problems. It is not unusual today to have new parts that are defective. Did you have same problem with old starter? Has the new starter ever worked correctly? Bench test would be good, because you already jumped the S terminal to good battery and no start = bad solenoid/starter. Also would check voltage on purple S wire at solenoid terminal and at firewall connection. This wire could have been the problem and then the new starter was bad - just a guess from your posts.

 

Have to ask:
If Automatic is it in park
OR
If 4speed is the clutch depressed?
Both of these (or their failed safety switches) will cause your symptoms.
Else: agree with others; pull the starter and bench test - easy to accomplish with a set of jumper cables.

 

I will pull the new starter and bench test it with 12V. I diagnosed the problem as a defective starter before which is why I changed it. It stands to reason I might have received a defective starter because the car's symptoms haven't changed. That would be a shame because I have also received poor electrical components before...that's why I sprung for a new unit this time.

 

Car is auto...yes it is in park.

Also does not start in neutral. 12V present as the NSS between purple and purple/white wires. Jumper across the NSS does not solve the issue.

 

I jumpered a 12ga wire from the purple post on the NSS to the S terminal on the starter solenoid to try and eliminate a break in the wiring with no success.

Yes...same problem with old starter.

 

What I am saying is you should have 12v at the S terminal, not 8v.
This could be the original problem with the old starter, then you put a new starter on that had its own problem. The best thing would be to find the voltage drop, and my guess because you checked the voltage at the switches, is that it is the purple wire. It is common for the purple wire in the engine compartment to have issues, including the connector at the firewall.

 

Wouldn't the jumper from the NSS purple to the starter solenoid s terminal take any issues with the purple wire or connectors out of the picture? Or am I reading the wiring diagram incorrectly?

 

Maybe, If you had a large enough lead to carry the current that distance and also decent connections on each end. You said you were getting 8-9 volts at the S from the purple wire. You had 12v at the NSS. The only thing in the middle is the firewall connector and the purple wire.

 

See highlighted comments above.

 

I cleaned every terminal. I removed both ends of both ground cables and now everything is free of even one speck of dirt (on the cables, brackets, frame, block). However, even though both ground cables passed continuity test I suppose there could be some internal corrosion under the insulation I cannot see. The small black wire is grounded to the engine block through the bolt which connects the front starter support bracket to the block.

After I cleaned every single gound terminal my voltage the S terminal with key in start position is now a little over 9V.

Does anyone have a picture of the stock location of the firewall connector? That would be very helpful my photo diagram from Dr. Rebuild is still in the mail.

I will also be pulling the starter tonight to bench test to confirm it is a good starter. But before I yank it again I'd like to test the firewall connector to starter solenoid voltage and see if my drop occurs there.

 

It is the purple wire - check post #21
https://www.corvetteforum.com/forums...starter-2.html

 

Are you certain the engine is not locked up?

 

Dark thought but good question.

 

That is a possibility, all the more reason to bench test the starter as I said in post#4. While it is off, it is easy to check rotation on the flywheel.

 

Pulled off new starter and new solenoid last night. Bench tested it and it failed. Solenoid was engaging but not giving motor power. Starter was good when tested directly.

Then I tested old combo that came out of the car originally with opposite results. The solenoid gave the starter power but the starter would not turn. So long story short I swapped the old solenoid onto the new starter, tested it, rechecked the grounds and reinstalled. She fired right up no problem.

Thanks for the support everyone.