... determin[ing] the pin-outs of a Delco AM/FM radio ....

Since Delco is GM's electronics arm, why not ...? Or a car audio place?

The latter suggestion worked, I was even able to purchase the proper plug
with pigtail leads, the radio is now in service, and I didn't even have
to trace any wiring!-)

Thanks, everyone, for all the suggestions.

--Myron, W0PBV.
--
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)