Help with Temp, Gas, Oil Alt gauges FREE VIDEO INCLUDED!

You dont need ground lead all the back to battery. Chassis ground point somewhere under the dash works. If your inst' housing is out of the dash, dangling from its harness connectors, attach a ground jumper from the inst' housing to the chassis. A permanent ground wire from inst' housing to chassis is wise. Of course all your ground attach points need to be checked. Painted surfaces don't work. Hunt unpainted places. I've recommended pulling the left kick panel and add a screw and a wire with ring terminal from there. When my ground wire reaches about 6 inches from another ring terminal under a screw on the inst' panel, a male/female spade connection so my ground wire will unplug like any factory connection.
Majority of solid state IVRs will function ( 5 volts out ) with as little as 9 volts in. Again I don't know all about the fancy RTE unit.