First of all, 8.2 volts is too low, but the starter should at least try to turn slowly.
By "solenoid wire", do you mean the smaller wire that powers the solenoid or the really fat battery cable
First of all, 8.2 volts is too low, but the starter should at least try to turn slowly.
By "solenoid wire", do you mean the smaller wire that powers the solenoid or the really fat battery cable attached to the solenoid? The smaller one should have 0 volts until the ignition switch is turned to "crank', then it should have whatever full battery voltage is at the time.
If you're describing the fat battery cable at the starter, 6.85 volts subtracted from the 8.2 volts at the battery means you're dropping 1.35 volts across the two battery cables. That is also way too much. The acceptable standard is 0.2 volts across any single mechanical connection AND a maximum of 0.4 volts in either the positive cable circuit or the negative cable circuit.
Two things can cause excessive voltage drop. Excessive, undesirable resistance or excessive current draw. Excessive resistance is caused by frayed or corroded wires, loose or corroded mechanical connections, or cables that are too small. Excessive current is caused by a starter that is spinning too slowly or is partially shorted. A partially shorted starter can appear to work properly when bench-tested off the engine because it isn't being loaded down. The starter can spin too slowly due to rubbing rotating parts caused by worn bushings.
By testing between the cable on the starter and the engine block, what you have done is to determine there is a point of excessive voltage drop. Now we have to narrow down its locat