Switched Power on OMC wiring

[Drewski Canuck]

I have done a rebuild on a boat with an early 90's OMC wiring harness to a 110. Had a slow battery drain over the last few years, and it would take a couple of weeks to kill the battery. I always assumed it was a bad battery, or just life with no charging for long periods of time.

Today when putting in a new stereo, etc, I noticed my voltage guage is always on. Obviously, when rewiring gauges, I missed the switched power and took power off another gauge which is fed from the fuse block.

I know the Tach wiring harness is switched power, as it is not on when the engine is not running. Only other feed I can think of for the voltmeter would be in the throttle assembly from the keyed power, which may have been missed when the boat was taken apart for updating the interior carpeting.

Can anyone tell me if it is possible to feed the voltmeter off of the Tach? I am assuming the tach be measuring voltage or Amperage to convert to RPM's??? If taking power off the tach would not affect the reading of the tach guage, I am thinking this would be easier than taking off the throttle / key assembly to find the missing connection for keyed power on the wiring harness, but I think this can only work if the Tach guage measures something other than volts to convert to RPM's, as otherwise the voltmeter would be unreliable.

Any help would be much appreciated, as what has been done to this boat does not follow any wiring diagram from the original manufacturer.

Drewski

 

[mikey]

find key on power at the fuse panel with a test light

 

[Drewski Canuck]

I did not run key on power to the fuse block when I re wired. The boat had "pop" fuses on the dash panel, all of which were corroded. I went to a new style AT Fuse system, as opposed to old glass Buss Fuses. Nothing would have been switched power, as livewell, bilge, stereo, VHF, Fishfinder, etc is on the fuse block. What remains as option is the tach wire set or going back into the throttle assembly and finding power off of the key switch. I would prefer doing the former if possible.

Thanks all the same.

Drewski

 

[wstcoaster]

i think the result of taking power off tack imput would be negible as volt meter uses so little juice

 

[trendsetter]

The tach reads pulses from the rectifier. Not 12v so that will not work. However there should be a 12v power line on the back of the tach for the light inside the gauge. Use that one.

 

[Drewski Canuck]

Thanks trendsetter. Again, this lousy pop fuse system caused me to direct wire from the fuse block to the guage lights and power for the guages. So again, I am looking at taking the throttle control assembly off to see if I can find a switched wire to run forward to the voltmeter. If I ever catch the designer of these dash mounted pop fuses, .... These are a really dumb idea at the best of times, as if it is popping regularly, there would be a serious problem. AND given that these lousy fuses can't handle moisture, why would you put them in a boat in the first place? IF there is a Sylvan technician available, go slap your engineers upside the head. Little wonder these things had such a short following before being discontinued.

Drewski

 

[trendsetter]

Does your tach work currently? There should be three wires going to the back of the tach:

Grey: Tack Signal / Send
Purple: 12v ignition & Lamp power
Black: ground

Use the 12v ignition wire to power the voltmeter.

 

[Drewski Canuck]

THANK YOU!! I figured the purple would work, just could not find a schematic for some reason for OMC for the Tach and didn't want to damage the sender. For a pointer, I have been using insulated quick connectors, which have a plastic boot that seals one to the other, and have been coating the internal connectors, and all wires before crimping in dialectric grease. I actually had pretty bad corrosion on the wires INSIDE THE CRIMPS, as well as on the old bullet connectors, which really aren't that water tight.

One thing you have to love about salt water is how effective it is at destroying copper wiring assemblies, and everything else electrical. Hopefully this time I will have the problems solved.

Drewski