1992 Baja 236 with 7.4 bravo one TBI.Start boat up,temp starts coming up.Hits 160 then jumps to 200 and back to 160 intermittently.I changed sending unit and thermostat.I ran seperate wire from sending unit and seperate ground to battery.I am getting a constant 12v power to gauge.When I test sending unit wire,voltage jumps from around 4.5 vdc to 8 and then back everytime the gauge jumps.I tested the gauge by taking sending wire off and grounding it.Gauge pegged.I dont think it is the gauge.I didn't change it yet.Anyone have any ideas?