tachometer (accessory) question

[johnyrude200]

I am getting ready to install an OMC tach into a helm I built, but the one I have has a cracked bezzel and I am considering going with a replacement. The unit I have is a salvage off of a scrapped boat, so I don’t have wiring instructions. I found this one on Ebay as NOS and was wondering if it made a difference what unit I buy (it’s originally dubbed for an OMC snowmobile). Figured it didn’t make a difference, but wanted to ask.

261752
http://www.ebay.com/itm/OMC-JOHNSON-EVINRUDE-SNOWMOBILE-NOS-TACHOMETER-261752-/131679455795?hash=item1ea8b50a33:g:jDUAAOSwJcZWc~3A&vxp=mtr

The motor I have is a ’93 50hp on a small tritoon I’ve been working on for a couple of years at this point (trying to finally get it done). The tach I currently own has the quick connect that would normally plug into the accessory port on a remote control box. I’m guessing if I pull that tach apart, I can disconnect the leads and put them on the one I’m considering?

[mr-asa]

Bezels can be replaced sometimes, the lenses are fairly cheap on eBay. Is the retaining ring easily removable?

Depending on where the tach gets it’s signal, there might be differences in various motors because of the amount of cylinders in the motor. Beyond that, I can’t think of any issues with using another tach

[frankr]

Just about all (electric start) outboards built within the last 30 or 40 years use a tach that gets its signal from the alternator. They count the AC pulses from the alternator. Check it out, but I think your 50hp has 5 pulses per revolution.

So, the question becomes does the tach in question have a selector switch to determine the number of pulses? Well backing up, I suppose the first question is whether or not it is an alternator tach.

I don’t know the answer to those questions.

[fleetwin]

Yeah, I wouldn’t chance spending $40 on that tach designed for the snowmobile….A decent used OMC outboard tach shouldn’t be too tough to come by. 93 was one of the first years for the larger alternator on the 40-50hps. So, if you have the larger alternator (equipped with finned rectifier/regulator) you would set the OMC tach to position "6". If your engine has the smaller alternator (equipped with the four wire conventional rectifier), set the OMC tach to position "5".

[outbdnut2]

There are a lot of differences in tachometers. OMC used Airguide tachometers for many years. Here’s a link to airguide marine tach models and what they fit. Note the model 653 is shown for private label OMC tachs with magnetos, model 654 is not:
Dave

http://www.classicboatwork.com/classicp … 0Guide.pdf

[johnyrude200]

I picked up an OMC Tach, newer than the older unit I started with. The newer one does have a pulse switch adjustment, but it does not have any pre-wired leads.

Does anyone have a tachometer wiring diagram they could share? It has a battery, ground, signal, and ‘sync starboard and sync port terminal poles.’ Than a purple lead coming off the back light lamp.

The older unit I have has everything pre-wired with a quick 3-prong accessory plug.

I’m guessing grey goes to pulse, black to ground, purple to battery (these all come from the engine harness out to the motor)? Purple light lead ties to the battery pole for positive, black goes to ground which lets the light illuminate. There’s a 2nd purple wire coming off the engine harness where I believe that lead splits for other accessory power?

Thanks for the help.

[fleetwin]

OK, never seen one of these….
But, the grey tach lead goes to "signal", purple B+ (switched on power from key switch) goes to "battery", black ground goes to "ground", the purple lead coming off the instrument light would go onto your running light switch or the purple B+ if you want the instrument light to be on whenever the engine is running. I’m sure that "sync" terminal is unused in your application…
Again, have never seen one of these tachs, obviously for the new ETEC engines. Perhaps Will can provide more info….

[johnyrude200]

I didn’t realize it was that new! Although I did find a P/N and see they are being sold today through BRP as a non-system check tachometer. Picked one up used on ebay for around $30.00, sure beats paying $120.00 retail.

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