Can i use the orange transmission wire to power my HEI.I changed the stock trans. out and put 350 trans.in car,so won't need orange wire.car is 66 cutlass,thanks

 

Yes, that is a 12V switched circuit.

 

Looking at a wiring diagram for a '67 Cutlass, which should be the same regarding the orange transmission wire of which you speak, the wiring diagram states that all wires are 18 gage unless otherwise specified and unfortunately the orange transmission wire is not otherwise specified and so would not be of adequate gage size to support feeding power to the HEI. I would use that 18 gage transmission wire to switch on a 20 amp relay wired with 12 gage wire to power the HEI.

 

On the 1966 cars that trans wire is fused at 9 amps. That fuse is fed by the same wire that runs to the coil, through the resistor wire, but that part is unfused, which is interesting.

 

The orange wire is fine for the MSD trigger. The separate power wire should go to the battery and be heavier gauge.

 

Joe(s), I understood the OP wants to use the 9 amp fused orange 18 gage transmission wire to power an HEI, and tracing the circuit back to the source (energizer) not even a fusible link is shown. Is it possible that there is an overload breaker built into the ignition switch? Looking at the wiring diagrams for the other series vehicles and even the L6 wiring diagram, they all show fusible link protection in the circuit feeding the ignition switch, maybe there is an error in the wiring diagram for the V8 "A" body.

 

You are correct. There is no fusible link. The 12 ga red wire from the junction block feeds the ignition switch. The pink 16 ga wire from the RUN terminal of the ignition switch feeds the coil resistor wire directly, again without a fuse. This same wire also feeds the 9A TRANS fuse that feeds the orange wire and the 9A INSTR fuse that feeds the dash.