16V electrical gurus needed...

[amalventano1 at tds.net (Allyn)]

> Okay, teach me what you think....

OK, here's how it works...
Say your system is drawing 10 amps of current across that ground wire. If
the ground wire had only 1 ohm of resistance, this ground wire would drop 10
volts across it. What does this mean to you? The vehicle systems ground
potential floats upward by 10 volts, which means they only have 2-3 volts
left to do anything with.

It's basically a vicious cycle. The more current drawn, the more voltage
dropped, the less voltage available at the end of the line to cause the
current to flow in the first place. In the end you have barely enough
current to roll the starter over, or just enough to crank, but while
cranking there is not enough voltage available to the rest of the car for
the ignition coil, fuel pump, etc to operate properly.

Once running, the alternator counteracts the effects of the weak ground
connection because 1. There is no more bulk load from the starter cranking
and 2. The alternator is grounded straight to the engine, so no high
resistance issues to be had there.

The best way to check for a bad ground cable - measure from (-) of battery
to the cylinder head or other part of the engine. Measure voltage while
cranking the engine over. Anything more than 2 volts points to a weak ground
cable. Same goes for battery (+) to starter (+), though based on how short
that cable is, I would say >1 ohm is on the bad side.

The best way to check the alternator charging cable is to measure from (+)
of battery to the red lead at the alternator. With the engine running, fire
up every load you can think of (A/C, headlights+brights, etc), and measure
on voltage scale. Again, anything more than ~1 volt points to a weak ground
cable.

> How can
> one hope to keep the ohms down and still drive them?

The main culprit for high resistance over years is the ground line. Its
insulation is cheesy and breaks away over time, leaving the stranded copper
to corrode, increasing its resistance. The second worst is the alternator
charging line (especially the portion that runs from (+) to the starter).
The many other wires throughout the car are smaller, carry less current and
have better shielding, which keeps them in at least decent shape even after
20 years.

> The ohms I had there BEFORE I fixed the ground cable was 180 or so.

See this chart for what you should be getting:
http://www.interfacebus.com/Reference_Cable_AWG_Sizes.html
Typical starter cable is 4 gauge, which is 1/4 ohm for a thousand feet. I
would think 180 ohms is a tad higher than the .001 expected reading.

HTH
Al