I don't think they make just that yellow triple outlet. You can buy a triple outlet and splice it in to where you want it to go. That yellow triple plug is part of the 66 year harness (repro), it's built right in. I have a early 66 car and my original harness had the black triple plug running off the fuse box. I bought a new 66 harness and there's no black triple but there are two other triples, one red and one yellow. Both are for accessorie feeds. They do sell a 65 harness that would also work for a early 66 car, which is this. You can see the black triple running off the fuse box. 14401-N Mustang Underdash Wiring Harness With Lights 3-Speed Heater After 4/1/1965 | CJ Pony Parts
This next harness is for a later 66 and there's no black triple running off the fuse box but there are two other triples, one red and one yellow. This is the harness I used for my early 66. 14401 66 Mustang Underdash Wiring Harness 1966 | CJ Pony Parts
My car does have several options that gets pluged into these triple outlets. There are other female single outlets running out off your harness as well. These are also for options like fog lights. In most cases if your car did not have an option, the outlet running off your main harness will be taped up hiding that outlet for the optoin you don't have. Those female plugs are live.
I have an extra black triple outlet that comes off the fuse box from my original early 66 harness sitting around just like in your picture. Why can't you use that one and splice it in where it needs to go?
Hello. The part that you are looking for is the accessory feed. It does indeed clip into the front of the fuse box in the slot for the (drum roll) accessory fuse. Nobody reproduces these as far as I know. The part number is C5ZB-14A318-B. I do know of a person that has NOS accessory feeds for about 85 bucks. Let me poke through some boxes and see if I have a decent one somewhere. I'm pretty sure that I must have a few of them. If yes, you can have it.
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