# 399 engine speed sensor location???



## Kaen3e (Mar 21, 2015)

I have exhausted my internet search abilities and the dealer is no help... after putting a new clutch, hydrolic pump, water pump and power steering pump on my early 399 4x4. I wanted to fix the tach not reading accurately I'm trying to locate the engine speed sensor and I'm not having any luck. Does anyone know where this bugger is? The dealer has been no help beyond taking my money


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## stack em up (Mar 7, 2013)

No idea what a 399 is, but if it's an electric tach, maybe it uses the alternator as its source? Alternators with tach would have 3 prongs on the plug.


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## Kaen3e (Mar 21, 2015)

Massey 399 tractor. Made in 1987


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## stack em up (Mar 7, 2013)

Is the tach not working at all? Or just inaccurate?


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## javafarmbatavia (Jan 28, 2016)

What engine and serial number do you have?


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## slowzuki (Mar 8, 2011)

Most likely a tach signal. Was the alternator replaced at some point?


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## Kaen3e (Mar 21, 2015)

Alt is original to the tractor. The tach works but idle is at 1700 and max is off the dial. Engine # 
1w31159*uz902266p. It's early 354.4 Perkins made in 87 in England.

Thanks to all taking interest in this


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## slowzuki (Mar 8, 2011)

The tachs that read from the alternator get their signal from part of the regulator circuit that runs the rectifier circuit that turns the multiphase ac into dc voltage that charges the battery. In all likelyhood a diode or similar is burned out.

My MF had a similar problem, the alternator still charged fine but the engine running signal wouldn't output power so my bosch 3 point hitch computer wouldn't unlock. There are something like 4 little special output tabs on the bosch style alternators (mine was not bosch).

The main rectifier diodes were fine but the little ones for those terminals are built into the regulator circuitry. It was cheaper to get a made in eastern europe replacement with twice the amps than it was to get a new regulator.


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