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Okay, I'm trying to "jump" the starter on my '03 V8 ---- the reason is that I just want to spin the engine to check some things out. I am doing this with the car essentially "off-line" ---- in other words, by-passing the ignition, fuel delivery, alarm, electrical systems, etc.

So, I've completely disconnected the car's battery --- both pos & neg terminals and all cables that attach (e.g., as if no battery in the car). Using an external battery, I've clamped a cable from the battery positive terminal to the positive (red) cable which goes directly to the starter, and I've also wired the (white / red) wire which goes from the starter solenoid relay to the starter solenoid (downstream of the relay, so directly to the solenoid) directly to the battery positive terminal ------ so, both the starter and solenoid should be seeing +12V.

To ground the circuit back to the negative battery terminal, I've clamped a cable on the negative battery terminal and onto the bell housing of the car.

Problem is, when I "throw the switch", I get nothing ---- starter does not operate. Am I wrong in assuming that the starter & solenoid are negative-grounded through the block (i.e., does it connect to a ground return cable somewhere instead that I should be tapping in to) ????

OR, is it possible that the bell housing is either non-conductive ---- magnesium alloy perhaps, instead of aluminum ??? ---- or, is not well-enough electrically coupled to the block to complete the return circuit ???

What the heck am I doing wrong / stupid here, guys ?!

See the attached diagram for reference....
 

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If that's really the right diagram, it looks like you are on the right track.

Why not just run a cable from the negative post of the battery directly to the housing of the starter? I don't think that's your problem, but it would take that part of the circuit out of the equation. Everything seems well grounded together on these cars.

And I seriously doubt the bell housing is mag because it would be all corroded by now on all our cars. You can use a regular volt meter to test continuity between the bell housing and the starter motor. Just set it to that position where it beeps when you touch the two leads together and then touch the ends to the bell housing and the starter housing.
 

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Discussion Starter #3
If that's really the right diagram, it looks like you are on the right track.

Why not just run a cable from the negative post of the battery directly to the housing of the starter? I don't think that's your problem, but it would take that part of the circuit out of the equation. Everything seems well grounded together on these cars.

And I seriously doubt the bell housing is mag because it would be all corroded by now on all our cars. You can use a regular volt meter to test continuity between the bell housing and the starter motor. Just set it to that position where it beeps when you touch the two leads together and then touch the ends to the bell housing and the starter housing.
Thanks for the help :)

I just discovered the problem --- and it was a bonehead move on my part.

The auxiliary battery I was using was dead, or at least not putting out enough amps to turn the starter, (although the damn thing tested "good" by my meter ---- which is another story --- meter was miss-calibrated). I was in a hurry and did not do my due diligence with checking out all the equipment. ( :mad: at myself , because I know better)

Anyway, I got it sorted --- swapped with a good battery. Starter spun as it should.
 

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I thought about suggesting to check the health of the battery, but then I thought surely...
 
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