Engine unable to turn over with lights on? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 06-21-2012, 10:09 PM
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Engine unable to turn over with lights on?

Working on a 1930 model A street rod. 350 Chevy engine, 4 speed manual transmission. Top of the line battery. The car previously had a 4 gauge copper ground wire that went from the negative post on the battery to the frame that was about 2 feet long. We thought we would upgrade by going to a 1/0 ground cable from the battery to the engine block (about 7 feet long). That is the only change that we made. When the car was grounded to the frame the engine would turn over with the lights on. Now that we have upgraded the ground cable from the battery to the engine block, the engine will not turn over with the lights on. Does not make sense to me. Anyone have any ideas why this is happening?

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Old 06-22-2012, 03:50 AM
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Is there any other ground connection other than the new cable to the engine block? You should have the body and frame grounded as well as the eng block. Try running a temp cable from the eng block ground point to the orig ground point on the frame, if that fixes it then you have an open loop in your ground plane.....
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Old 06-22-2012, 04:48 AM
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As a general rule I always run the main ground from the battery to the engine. I also run a smaller ground strap from the engine to the frame and another from the ground on the battery to the body. This will make sure there are no grounds trying to pass through stuff like motor mounts and body mounts.
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Old 06-22-2012, 11:18 AM
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Lights are grounding out to the body and not supplying sufficient power to the starter circuit.

Why are you starting the engine with the lights on???

Cheap Chinese cable, not enough strands.
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Old 06-22-2012, 04:15 PM
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Little..... I don't understand your post....Lights are grounding out to the body and not supplying sufficient power to the starter circuit.

Are you saying the light circuit provide power to the starter circuit?
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Old 06-22-2012, 05:48 PM
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Start with this. Clean the battery terminals. Clean the connections to the engine block, and the frame, and the body of the car.
Do you have a voltmeter?
Do you know how to check voltage drop on a single cable?

To check voltage drop, take the red lead of the volt meter, touch the frame of the starter, NOT ANY electrical terminals. Touch the negative battery post. Without cranking the engine, the volt meter should read zero.

Crank the engine, while leaving the volt meter hooked up as above. The volt meter should read less than .5 volt. If more than that, something is wrong with the cable the cable.

This page is a longer read, but explains voltage drop much better than I can.
http://www.vernco.com/Sparks/id606.htm
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Old 06-22-2012, 09:04 PM
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Quote:
Originally Posted by DanielC
This page is a longer read, but explains voltage drop much better than I can.
http://www.vernco.com/Sparks/id606.htm
That is a great site. Thanks for the link!
I am an electronic tech myself and I just learned something new.
Russ
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Old 06-26-2012, 01:29 PM
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Battery cable end not installed all the way down on the post

Thanks for all the great information. I checked everything out as suggested and it turned out that the problem was that the new battery cables would not fit all the way down on the battery post. They were installed about half way down the post and tightened. The person working on the car did not have the special tool to spread the cable ends apart and he knew better than to beat them on with a hammer. I cleaned the posts and cables, spread the cable ends apart, pushed them all the way down on the post, tightened them up and now the motor will turn over with the lights on. The reason that was needed in the first place is the driver was at a stop light at night. When the light turned green, he let the clutch out a little too fast and killed the motor. There were cars behind him honking the horn so he turned the ignition switch to restart the car and nothing happened. As a last resort he turned the lights out, turned the key, and the car started and he was on his way.
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