Tachometer 1978 35hp Johnson 35EL78R

[danielb1]

I have a 1978 35hp Johnson 35EL78R motor on my pontoon that has a Tachometer and battery meter that were not hooked up. The battery meter was simple but there is no grey or grey striped wire at the instrument panel for the the tach. Being that I have a manual choke on the motor I decided to use the electric choke wire from the harness. I disconnected it from the choke and connected it to the yellow-grey wire coming from the stator on the connector block right above the choke solenoid.

This tach is so cheap it doesn't have a zero adjustment and it sits at about 200 RPM with motor not running. The existing tach only has a 1, 2, 3, or 4 pole choice (no six pole that most of the comments I've read say that I would need to use). At 4 the tach gets buried, at 1 the tach varies from 1100 to 4500 RPM with motor running out of gear parked at the dock. When in gear the throttle moves a bit farther so I may even bury this tach but I didn't have time to check it out (mesquitoes were starting to swarm). Set at 1 the tach seems to be getting twice the actual RPMs (I don't have a tach test meter to test the accuracy out). I'll try the 2 & 3 settings tomorrow.

Is it possible that this 1978 35hp motor has less poles than I've read for Johnsons or is there no way I am going to get this tach to work accurately with this motor?

If not, what is a good, cheap ($20-$40) tach to use?

also:
I'd like to hook up a car stereo and pair of speakers, can this motor supply enough juice to charge the battery, run the navigation lights, instrument lights, and the stereo?

How about a microwave oven, air conditioner and hair blower . . . (just kidding)?

Thanks in advance!

 

[F_R]

Re: Tachometer 1978 35hp Johnson 35EL78R

I would suspect the tach is designed for battery or magneto ignition (runs off the points). Don't wreck it, it should be worth something in the old-boat world. Also, reading above zero is normal on a lot of tachs. They will read correctly when running.
Your alternator puts out 5 amps. Just add up the load you are putting on it and allow a few amps to keep the battery up. Not a whole lot to spare. Remember, it isn't putting out anything at anchor but your blaring stereo is still sucking out amps from the battery.

 

[danielb1]

Re: Tachometer 1978 35hp Johnson 35EL78R

I thought that it put out more than 5 amps since it has a 20 amp fuse spec'd out for the 12V line in the wiring harness schematic.

BTW, I now realize that I need to get the correct 12 pole tachometer.

 

[jtexas]

Re: Tachometer 1978 35hp Johnson 35EL78R

tinytach.com sells digital inductive tachs for $36 - my local OMC parts dealer has a box of used tachs for $45, might find something like that near you.

If you have the OMC control box, there's a 3-wire socket under the keyswitch, covered by a rubber boot, that has the gray, purple and black (tach, 12v switched and ground). forget which hole is which but easily determined with a voltmeter.

The 20A fuse also supplies battery power for the starter solenoid and choke, is why it's 20 amps.

Running lights, depthfinder, bilge pump, shouldn't be a problem for your alternator (assuming a good battery)...not sure about the tunes...a deepcycle battery might be a good investment if you can tolerate the extra weight.