I swapped out a 5.4 2valve engine, when you turn key to start mode the coil at the starter relay positive side becomes 12.8 volts to chassis ground. The negative side of coil to battery positive shows 9.8 volts. Needs to be at least 10.5 volts to energize coil. The negative side of coil from cpu ? Need help

 

What year? What model? You are correct, a lot of the later models used a electronic switch in a smart junction box to activate the starter solenoid. The negative side of the coil should be close to zero for it to crank over. When you get 12v on the + side of the coil, if you jump the negative side to ground manually it should click in and try to turn over. Be careful, make sure you are in park in case it starts.