Gauges erratic won't start

Hey all, I have a 99 accord ex v6 that ran fine when purchased a month ago, ended up having a couple bad oil leaks and using coolant. I installed a lower mileage engine and now will crank won't start gauges are erratic and green key indicator flashes and dims. Did manage to get it started yesterday after cranking and ran great. Was tried this am and now has all the same issues. Used all the parts that were on the car originally except sensors that were installed onto engine that was installed. Any thoughts? Grounding issue? Thanks.