engine keeps cranking after it has started.

[RonD]

It was used because all the wiring harness's were already setup for the fender mounted relay
Just cheaper to add the smaller red wire until a new harness was designed and in the supply chain

If you remember the older fender relay setup there was the larger battery positive cable on one larger post and another larger cable on the other larger post and this cable ran down to starter motor
When relay was activated 60amps ran thru the relay down to starter motor to activate it, no relay in this type of starter motor

So to convert over to the relay type starter motor they just moved the starter motor's larger cable over to Battery Positive post so it have 12v full time
Then added the smaller red wire in the fender relay to active starter motor relay
Simple conversion
And it took a few years to make sure these new starter motors with relays didn't have issues, lol
And to design a new harness and longer battery positive cable that was long enough to run directly to the starter motor