EVANLA 33 is correct. I assume by your question that the "battery" side of your coil is not hooked up.
To make things simpler for you, click on "Classic Tech". You will find an area close to the top that says Wiring Diagrams. Click on that and thanks to pcfrisch, you will find pictorials and schematics for a range of classic mustangs. Click on 65 wiring diagrams and then click on "65 Mustang, ignition, starting & charging". Find the ignition coil and trace the wire on the diagram. Look up the number for the wire colors and you'll see it says "red-green". That means a red wire with a green stripe. Find that wire on the harness inside your engine compartment. It should have a 90 degree connector on it (see pic). That's what goes on the battery side of the coil.
If, in your opinion, that entire harness is in poor shape, you can purchase a new one for about $35 from any major Mustang parts supplier. Their harnesses have the correct colored wires and connectors. They are pretty easy to install. :bigthumbsup
If you need more help, let us know. Good Luck. :winks
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