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Author Topic:   Mercury 2005 50hp 4 stroke EFI - Reversed Polarity
tnbiker007 posted 07-26-2009 09:58 AM ET (US)   Profile for tnbiker007   Send Email to tnbiker007  
Help. I have a 2005 Mercury 50 hp 4 stroke and have reversed the polarity when hooking up the battery.

I tried to start it with the reversed polarity but only once. Nothing happened so I stopped. No smoking, no fried wires, no electrical burn smells.

I hooked the battery back up correctly and the battery reads approx 12+ volts with my multimeter so I feel confident the battery is still good. However, the motor will not start. The instrument panel/lights works and warning beep sounds. The trim motor works. However, the starter will not spin the motor.

All 4 fuses look good (2-20a, 1-25a & 1-5a). I can bypass the starter solenoid and the start motor spins but the motor will not start so I suspect something in the firing process is screwed also.

Any ideas on where I can start on trouble-shooting this? I'm guessing the solenoid will need to be replaced to at least get the starter motor working again. From there what would you recommend trying next?

Could there be more fuses I'm overlooking than just the four mentioned. Is there any type of resets (like a breaker) I need to check before replacing parts?

ScottS posted 07-26-2009 11:29 AM ET (US)     Profile for ScottS  Send Email to ScottS     
If the fuse was okay, then some other part of the circuit was damaged. Just guessing and replacing parts will get expensive. Get your hands on a Mercury service manual for this motor and it will walk you through the steps to test each part.

Here's what the Mercury Racing site says:

"I accidentally reversed the battery connections when I reinstalled the battery. What potential damage could I have caused?
We strongly recommend that you have an authorized dealer inspect the vessel before returning it into service. The potential damage will vary from model to model. Although we try to design in protection for each component, limitations do exist.

The first item to check is the fuse or fuseable link. Most models have some type of protection in the circuits. You can replace the fuse with the correct size and test the system. If the fuse fails again, dealer involvement is recommended.

Other items on the engine that may be damaged include, but are not limited to the following: voltage regulators, rectifiers, tachometers, Electronic Control Module, isolation diodes and melted wiring. Boat related items may include the following: radios, radar, lights, wiring, etc."


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