Sorry, my mistake. You are correct. You only have the large diameter wire at the starter.

The test light theory still applies though. Connect the alligator clip from the test light to the neg battery cable. Have someone turn the key and touch the pointed tip of the light to the cable connection on the starter.

If the light illuminates, the starter is bad. If the light does not illuminate, test the circuit at different places to see where you're losing power.

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'69 Coupe, 351C
'05 Super Crew 5.4L
'06 Fusion SEL V6 (momma's car)