Starter Problems
Posting Guru
Joined: Aug 2010
Posts: 1,761
Likes: 8
From: Knoxville, TN
There has to be measurable resistance to get measurable voltage drop in any condition - it just can fall into the level where you're not sure if it's technique (not making good enough contact with the multimeter) or an actual problem with the wiring that's at fault, since at high current it takes less resistance to have an effect. I would agree with you though, that the most informative test would be voltage between the starter + lug and the starter body while cranking; voltage between the battery - terminal and something that should be grounded is meaningless though, and that's what he had been trying to measure. Between those two points, resistance is the relevant issue, even if it's more sensitive to measurement error.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Yes, that is true, but we are talking about high current, low voltage - hundreds of amperes. Because of this, that makes a tenth of an ohm either way a HUGE factor, the difference between an alternator charging or not charging, or a failed starter. It's "measurable" but not meaningful in practice, in these tests. This is an excerpt from the AA1 auto repair site:
"It doesn't take much of an increase in resistance to cause trouble. Let's say a 120 amp alternator operates in a circuit that has a normal resistance of 0.11 ohms. If that resistance were increased to 0.17 ohms because of a bad wiring connection, the alternator's maximum output would be limited to 80 amps. In other words, an increase of only 0.06 ohm (almost nothing!) would reduce the alternator's maximum output by almost a third! Under light load, the drop in charging output might not even be noticeable. But in a high load situation, the alternator wouldn't be able to keep up.
CHECKING CONNECTIONS
If you use an ohmmeter to measure across a heavily corroded battery cable or ground strap connection, or one with only a few strands of wire that make contact with the end clamp or terminal, the connection may read good because all you're measuring is continuity -- not the ability to handle a high amp current load. The connection may pass a small current, but when a heavy load is applied there may not be enough contact to pass the extra current. So how do you find these kinds of problems? You do a voltage drop test.
VOLTAGE DROP TEST
A voltage drop test is the only effective way to find excessive resistance in high amperage circuits. It's a quick and easy test that doesn't require any disassembly and will quickly show you whether or not you've got a good connection or a bad one. To do a voltage drop test, you create a load in the circuit that's being tested. Then you use a digital volt meter (DVM) to measure the voltage drop across the live connection while it is under the load. Voltage always follows the path of least resistance, so if the circuit or connection being tested has too much resistance some of the voltage will flow through the DVM and create a voltage reading."
"It doesn't take much of an increase in resistance to cause trouble. Let's say a 120 amp alternator operates in a circuit that has a normal resistance of 0.11 ohms. If that resistance were increased to 0.17 ohms because of a bad wiring connection, the alternator's maximum output would be limited to 80 amps. In other words, an increase of only 0.06 ohm (almost nothing!) would reduce the alternator's maximum output by almost a third! Under light load, the drop in charging output might not even be noticeable. But in a high load situation, the alternator wouldn't be able to keep up.
CHECKING CONNECTIONS
If you use an ohmmeter to measure across a heavily corroded battery cable or ground strap connection, or one with only a few strands of wire that make contact with the end clamp or terminal, the connection may read good because all you're measuring is continuity -- not the ability to handle a high amp current load. The connection may pass a small current, but when a heavy load is applied there may not be enough contact to pass the extra current. So how do you find these kinds of problems? You do a voltage drop test.
VOLTAGE DROP TEST
A voltage drop test is the only effective way to find excessive resistance in high amperage circuits. It's a quick and easy test that doesn't require any disassembly and will quickly show you whether or not you've got a good connection or a bad one. To do a voltage drop test, you create a load in the circuit that's being tested. Then you use a digital volt meter (DVM) to measure the voltage drop across the live connection while it is under the load. Voltage always follows the path of least resistance, so if the circuit or connection being tested has too much resistance some of the voltage will flow through the DVM and create a voltage reading."
Thread Starter
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Junior User
Joined: Jan 2001
Posts: 81
Likes: 0
From: Snohomish
I want to say Thank You all for the help, I replaced all of the cables, hardware, and sanded the surfaces. I also put a 6gauge jumper on the starter from the "S" to the lug for the cable coming from the Solenoid. She now rotates and I get to determine why I am not getting any spark.
I installed an MSD 6A Ignition Box, Summit PN# 850306-1 Distro, and a MSD 2 Blaster Coil along with a complete new wiring harness from Painless which has been anything but....
I installed an MSD 6A Ignition Box, Summit PN# 850306-1 Distro, and a MSD 2 Blaster Coil along with a complete new wiring harness from Painless which has been anything but....
Elder User
Joined: Sep 2014
Posts: 862
Likes: 7
From: like subarctic, brrr man!
Painless compared to doing your own, or fixing what you got 
Glad you've sorted it out!
One question about those MSD boxes, Do they require full 12 volts to the coil? and are you using a resistor wire or ballast resistor to the coil?
That I terminal supplies full voltage to the ignition coil for easier starts. On later models that circuit is handled by the ignition switch, and is FYI... Just wanna help sort a possible future wrinkle.
Glad you've sorted it out!
One question about those MSD boxes, Do they require full 12 volts to the coil? and are you using a resistor wire or ballast resistor to the coil?
That I terminal supplies full voltage to the ignition coil for easier starts. On later models that circuit is handled by the ignition switch, and is FYI... Just wanna help sort a possible future wrinkle.
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