What's this wire for?

vntned said

So the car in question is a '70 duster. I bought a engine conversion harness to run the later Mopar ecu. All seems fine except for one extra wire. It's the blue wire to the excitor on the alternator. The wire Ts off and goes back towards the coil. Is this for an electric choke?!

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Normally the blue wire on a factory harness goes to the voltage regulator.
Since it is T’d off and runs back I would suspect it’s an added on accessory feed, like for electric choke. (As already mentioned)
If the other blue wire goes to the regulator, then you should be good.
You could probably even remove the extra one if you don’t need it for anything.