posted 01-14-2012 07:47 AM ET (US)        

Two of the [System Check] warning lights are VRO and oil related. Would those just go unused?

Are the sensors already on the motor for the "Check Engine" and "Hot" lights? Or, would those lights be non-functional as well?

The wiring harness is plugged into (what I have read is) a warning alarm block. Would I unplug and discard this phenolic block when the [System Check Tachometer] is plugged-in? I do not see how [this phenolic block] could be used when replaced by the [System Check Tachometer]. I assume the warning buzzer will still work when the [System Check tachometer] is installed--[Is that correct?]

posted 01-14-2012 10:05 AM ET (US)            

The OMC or BRP System Check Tachometer connects to the engine wiring harness with an 8-conductor plug, part of the MWS wiring harness system which came into use c.1996 in Evinrude outboard engines. There are four circuits of separate alarm sensors in the plug and harness, corresponding to the four alarm indicators. The System Check Tachometer also contains circuitry which checks the functionality of the indicators when power is applied, and it has an internal aural alert sounder, also checked at power-on. The alarm circuitry in the System Check Tachometer monitors all four circuits and sounds an aural alert when any of them are active.

If you have removed the sensors which signal certain alarms, then, of course, the System Check Tachometer will no longer provide any indicator for those alarms. The four alarms are:

--Overheat, sensed by a thermal switch on the powerhead

--Low Oil, sensed by a float switch on the oil tank

--No Oil Flow, sensed by an electronic switch in the OMS pump assembly

--High Fuel Line Vacuum, sensed by a vacuum or pressure switch in the inlet fuel hose at the fuel pump

On a 70-HP Evinrude I do not believe there was ever a fuel hose vacuum switch, so you would not get an alarm about that condition.

If you have removed the OMS oil pump you will not get an alarm about the lack of oil flow.

If you have removed the oil reservoir float level switch you will not get an alarm about the oil level.

In summary, you will only get an alarm about the engine temperature. This raises a question in my mind: why bother with the System Check Tachometer if you will not have any use for three-quarters of its alarm function?

In the pre-MWS wiring system the alarm circuits were all wired into a WIRED-OR arrangement in which any of the four sensor could pull to ground the alarm circuit. When this happened the aural alert sounder was operated.

posted 01-14-2012 04:01 PM ET (US)            

The price on the internert for the system check tachs are about the same as the regular tachs, so it seems to make sense to go with the system check tach since it will easily plug in with the 8 pin connector on my harness.

You mentioned fuel line vacuum so that must be what the "check engine" system chack light is for on the tach???

The motor is a non-vro, so neither of the oil sensors will be needed, so as you say, the temp is the only one that would be functional.

One question on that though - do the engines come with the temperature sensors installed?