Ls3 voltage problem
 

Installed an ls3 engine with gm wiring and ecu in 67 vette using dakota digital gauges.

Everything works great except voltage with reads 17+volts as soon as i start it and then settles to 14 volts and as soon as i drive it or rev engine it goes back to 17+. Alternator has been checked off engine and is fine. Seperate checks of battery and dakota bim are in 13-14 range with engine off.

I understand ecu controls voltage

any suggestions - other than that car runs fantastic