I think I have a bad coil. First off, I'm trying to start the 250ci in my 66 C10 parts truck. The engine in the 66 is a 250 from a 1971 or 72 C10. I don't have a wiring diagram for a 71-72 truck, so I am making a few assumptions here.
From the firewall, the wiring harness appears to be identical to my 1965 except for 1 wire which is black. Please see the photo for clarification.
I have tried several combinations of yellow and black going to the positive side of the coil but I have no spark. I even disconnected the distributor side coil wire and connected a jumper wire to the negative side of the coil and still don't get any spark to the engine block. I confirmed that I have 12V coming to the positive side of the coil.
I measured 2 ohms across the coil terminals with it out of the truck and nothing connected.
So do I have a bad coil? Any other tests I should run? Is the yellow wire a "resistor wire"?
engine bay starter and coil wiring 
