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I am troubleshooting a rear wiper motor problem in a 2003 Ford Focus wagon (LE).

When I measure the voltage to the contacts (with the wiper switch on), i get intermittent (~4 s) voltage at 200 mV. This indicates to me that the relay is working.

However, when I plug in the brand new wiper motor it will engage for 2s, and then blow a fuse. I replace the fuse and it does the same thing. The motor says it's a 12V motor on the casing. This indicates to me that it's not receiving enough voltage, which is causing an amperage spike.

Question: Why would only 200 mV be being sent back to the wiper motor? Is this typical? Is there a transformer in the actual motor assembly that jumps it up to 12V that is malfunctioning?

If this were the case, however, it wouldn't do so on a brand new wiper motor.

Thanks, Scott

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Does it blow the fuse when the wiper motor is switched of as well or only when engaged? Have you checked to see if it is grounding out somewhere? –  Seminecis Sep 7 '13 at 17:20
    
No, the fuse does not blow when the motor is switched off, only once it is engaged. How do I check to see if it is grounding out? Thanks. –  svh160 Sep 8 '13 at 19:07

1 Answer 1

up vote 2 down vote accepted

Where exactly are you measuring the voltage and getting 200mV?

If you're seeing this at the connection for the wiper motor, then I strongly suspect your problem is upstream of the wiper motor. You need to get enough power (volts * amps) to the motor to run the wipers. Even if there were a DC-DC step-up converter in the motor (exceedingly unlikely), you can't create power out of thin air, so that 200mV that you measured would need to be capable of delivering a seriously high amount of current. It just doesn't make sense to design things that way IMO.

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This answer has led me to the conclusion that I need to do some more troubleshooting upstream of the motor. –  svh160 Feb 26 at 17:59

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