I have and hope to use a new repop( purchased 10 or more years ago) 71 340 4 speed cuda engine harness,trying to figure out why it is wired for a 2 pin ballast and a 5 pin ecu...how can i make this work? was it made wrong?

Unless you have an original (not a new one) 5 pin ECU don't worry about it the new ECU's do not heed the 5th pin. You can install the dual ballast for looks, but it is unneeded.

thanks Sniper,upon closer examination its a new repop points harness that came with a project car I bought,and that guy converted it to electronic,incorrectly.......fixed now :-)

All ECU plugs are ready for 5 pins, no one for 4 pins. If the harness is set for single ballast, then the unused pin wire is arriving nowhere down the harness.

Now, if the harness is set up for dual ballast, then the 5th pin wire (green with red trace) is arriving to the secondary resistor section. Which still if using a dual ballast with a 4 pins ECU, it won’t be any kind of load (althought still voltage present) on ballast secondary resistor or related wiring. Just with 5 pins ECU it will be in real use with some load.