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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3705
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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I have a 2000 Formula with 5.7L EFI Mercs. At idle the guage

Customer Question

I have a 2000 Formula with 5.7L EFI Mercs. At idle the guage reads appr. 10.5 Volts, and revving it 1500 takes it to 12.5. The volt meter reads 14.4 or so at the alternators, so what could the issue be ?
Submitted: 2 years ago.
Category: Boat
Expert:  Charles replied 2 years ago.
Hello, my name is***** will be assisting you today.Simply put it is corrosion. Locate the large round plug on the engine, unplug it. Make sure that the inside of it is really clean. You can use some contact cleaner and a Q-tip to get in there. Plug it back in and turn the key on. If it is still low. Test the voltage on the back of the gauge with the multimeter. If it is reading almost what you have on the battery, replace the gauge. If it is lower by several volts. You have bad wires inside the harness. The only way to repair this is either with a new harness or run a new wire from the engine to the gauge.

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