1970 Chevrolet Corvette engine will not turn over

Tiny
MMERTINS
  • MEMBER
  • 1970 CHEVROLET CORVETTE
  • 5.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 123,000 MILES
I installed a new interior with that, a refurbished wiring harness out of a 74 corvette. When I tried to start the car, nothing happened. I checked the voltage to the starter, 12 volts. The voltage dropped to 7 volts with the ignition in the on position and start position as well. I also checked the voltage at the coil as well, same story, 7 volts. I thought it was the neutral safety switch and tried to start the car in neutral, still nothing.
Could a bad switch cause this voltage drop or is it something else? All the grounds have been serviced and are in good condition. How do you go about checking the leads coming into the switch to make sure they are working correctly? Is there a separate ground for the switch? I am not sure what is going on, frustrated beyond belief! Any input that you have would be greatly appreciated. Thank-you
Mike Mertins
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Tuesday, July 29th, 2014 AT 7:16 PM

4 Replies

Tiny
CARADIODOC
  • EXPERT
Are you saying all you turned on was the ignition switch and then you had only seven volts on the larger starter terminal? You have either a bad battery or a dirty / loose cable connection. Start by measuring the voltage right on the battery posts. You should have the normal top-post battery, not GM's side terminal disaster. Measure the voltage right on the posts, not the cable clamps. If you find seven volts there, charge the battery at a slow rate for a couple of hours, then measure it again.

If you find over 12 volts on the posts, move your test probes to the cable clamps one at a time and measure again. Keep working down the line like that on both cables to the next accessible test points. You're looking for the first place the voltage drops a bunch. That's the point of the bad connection.
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Tuesday, July 29th, 2014 AT 10:31 PM
Tiny
WRENCHTECH
  • EXPERT
You used a '74 harness in a '70 car. Did those years have different ignition systems? Points vs HEI? HEI started in mid '74
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Wednesday, July 30th, 2014 AT 2:48 AM
Tiny
MMERTINS
  • MEMBER
No, I had 12 volts on the big post on the starter. It is when I turn the ignition to the on and start positions that I only registered the 7 volts on the smaller terminals on the starter.
The 74 harness is inter-changeable with the 70 harness.

I did check the battery early on when I first ran into this problem, it checked out fine. As mentioned before, all major grounds are in good condition.

I keep coming back to a possible problem with the neutral safety switch? I did try to start the care in all other transmission positions as well. Still nothing.
Suggestions?
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Wednesday, July 30th, 2014 AT 6:41 AM
Tiny
WRENCHTECH
  • EXPERT
Follow Doc's instructions
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Wednesday, July 30th, 2014 AT 12:06 PM

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