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Author Topic:   Johnson 48 SPL: Adding a Tachometer

FHAREN posted 03-31-2007 05:19 PM ET (US)
I have a Johnson 48 SPL. I'd like to install a tachometer but can't find much info on it around the internet. Can I just buy any tach? How to wire this thing up? Any help would be greatly appreciated.
bc posted 03-31-2007 08:51 PM ET (US)
I hooked up the one that was used with the original OMC 70-HP, when I purchased the 48 SPL. Don't know how accurate though. Seems to work ok.
jimh posted 04-01-2007 10:46 AM ET (US)
Most tachometers operate from pulses from the the battery charging coil using a half-wave rectifier tap. The frequency of the pulse train is proportional to the number of poles in the stator coil and to engine speed. If the tachometer is to have accurate calibration it must be matched to the corresponding pulse rate. The voltage of the pulses are clamped between near-ground and near-battery positive, so there is a more or less universal nature to the tachometer input voltage rating.
The Judge posted 04-03-2007 02:46 PM ET (US)
I have always had the best luck with OEm tachs. Especially with an OMC. If you have the side controls there is a rubber prong under the key that an OEM tach just plugs into...real simple.
Sal DiMercurio posted 04-04-2007 10:56 PM ET (US)
Jim, ...Huh????, you even confused me.
I agree with Nick [ The Judge ].
I've had more problems getting a non OEM tach to work right on any OMC engine.
You best buy one made by Bombardier for either Johnson Evinrude.
I tried a teleflex tach on my 1997 - 70 hp Johnson, & had to return it for one made for OMC.
There are numbers on the back of the tach & you must set it for your engine.
I think off the top of my head, your engine wants number 6 on the back of the tach.
Sal

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Author	Topic: Johnson 48 SPL: Adding a Tachometer
FHAREN	posted 03-31-2007 05:19 PM ET (US) I have a Johnson 48 SPL. I'd like to install a tachometer but can't find much info on it around the internet. Can I just buy any tach? How to wire this thing up? Any help would be greatly appreciated.
bc	posted 03-31-2007 08:51 PM ET (US) I hooked up the one that was used with the original OMC 70-HP, when I purchased the 48 SPL. Don't know how accurate though. Seems to work ok.
jimh	posted 04-01-2007 10:46 AM ET (US) Most tachometers operate from pulses from the the battery charging coil using a half-wave rectifier tap. The frequency of the pulse train is proportional to the number of poles in the stator coil and to engine speed. If the tachometer is to have accurate calibration it must be matched to the corresponding pulse rate. The voltage of the pulses are clamped between near-ground and near-battery positive, so there is a more or less universal nature to the tachometer input voltage rating.
The Judge	posted 04-03-2007 02:46 PM ET (US) I have always had the best luck with OEm tachs. Especially with an OMC. If you have the side controls there is a rubber prong under the key that an OEM tach just plugs into...real simple.
Sal DiMercurio	posted 04-04-2007 10:56 PM ET (US) Jim, ...Huh????, you even confused me. I agree with Nick [ The Judge ]. I've had more problems getting a non OEM tach to work right on any OMC engine. You best buy one made by Bombardier for either Johnson Evinrude. I tried a teleflex tach on my 1997 - 70 hp Johnson, & had to return it for one made for OMC. There are numbers on the back of the tach & you must set it for your engine. I think off the top of my head, your engine wants number 6 on the back of the tach. Sal