good advice, and also there can be contact resistance where the terminal
crimps onto the wire.

note also that even a small contact resistance on a low voltage, high
amperage circuit, can be serious. for example, suppose the current needed
to crank the engine was 200 A. this means that at 12 V the entire starting
circuit, including the internal resistance of the battery, the dc
resistance of the motor, and the reactive impedence of the motor, would
have to have an impedence of less than 12 V/200 A = 0.06 ohm. a 0.01 ohm
contact resistance could not be measured directly with most meters, but
the 200 A x 0.01 ohm = 2 V potential drop across the contact resistance
would be easy to measure.

i remember one time watching a guy trying to start his wife's car, which
had a big V-8. it wouldn't crank, but you could hear the solenoid
clicking. as it happened, i had my hand on one of the battery terminals,
leaning on the car. that terminal was warm. the other was cold. i made an
off hand comment to the effect: if this were a quiz, id say there was a
contact resistance on the warm terminal. but wait, this IS a quiz! i put
the a voltmeter across the contact surface where the terminal clamps onto
the battery (top post) - one probe on the top surface of the battery post,
the other on the cable terminal, and measured several volts when he
cranked the car. cleaning the battery post and contact area of the
terminal fixed the problem.

on the ground strap that bonds the body (just under the coil) to the port
side head on an '84 vanagon, i recently measured an 8 ohm !!! resistance
between the braided strap and the terminal, on the engine side. that was a
factory crimp gone bad, and would have made the ground strap essentially
useless. test was conducted with strap off the vehicle - concievable that
with snug bolt crimp was squeezed down and made better contact, but i
measured 0.25 V from body to head before repair, only a few mV after.