1998 merc green oil pressure light--hows it work

[bamasteeler]

so my 1998 merc 9.9 4 stroke has a green(good) oil pressure light on the front by pull handle that manual says should be illuminated when engine is running giving indication of good oil pressure. according to wire schematic the light has 2 wires..black goes to ground, yellow/red comes from Capacitor Discharge Module--assuming this is power for light. the yellow/red wire splits and goes to "low oil pressure" switch mounted on block.

My question is how does the "low oil pressure" switch work in this system to turn light off or on??

 

[carholme]

Re: 1998 merc green oil pressure light--hows it work

Are you using schematic 2D-1 in the manual:

It looks like pink is the supply wire coming from the module, becoming yellow/red out of the junction and supplying the light through the black ground. The oil pressure switch is just an on/off switch. Once oil pressure reaches the minimum on startup, the switch should close (illuminate light) and remain there as long as the pressure is higher than the minimum. If the oil pressure decreases to the danger point (minimum) while running, the switch will open, breaking the circuit for the green light and the light will turn off.

So really, the oil pressure switch is just the control for the black ground on the other side of the light.

Gerry

 

[bamasteeler]

Re: 1998 merc green oil pressure light--hows it work

Are you using schematic 2D-1 in the manual:

It looks like pink is the supply wire coming from the module, becoming yellow/red out of the junction and supplying the light through the black ground. The oil pressure switch is just an on/off switch. Once oil pressure reaches the minimum on startup, the switch should close (illuminate light) and remain there as long as the pressure is higher than the minimum. If the oil pressure decreases to the danger point (minimum) while running, the switch will open, breaking the circuit for the green light and the light will turn off.

So really, the oil pressure switch is just the control for the black ground on the other side of the light.

Gerry

yes that is the diagram i am using.

i think what is confusing me is if pink wire is supplying voltage, and the light has the black wire going to ground, then how is the "oil pressure switch operating the light?
being that only the yellow/red wire runs to switch and then terminates, what is the switch actually doing in the circuit to control the light? it would make sense if the switch was the only ground for the light, but with it having the black wire going to ground coming out of back of light capsule, what does it care what the switch does?

thanks for response carholme

 

[carholme]

Re: 1998 merc green oil pressure light--hows it work

Excellent find! The other 9.9s (four stroke)have the pink going directly from the oil switch to the light and the yellow/red as the power supply from the module to one side of the light.

On your engine, what colour is the wire presently connected to the oil switch?

Gerry

 

[bamasteeler]

Re: 1998 merc green oil pressure light--hows it work

Excellent find! The other 9.9s (four stroke)have the pink going directly from the oil switch to the light and the yellow/red as the power supply from the module to one side of the light.

On your engine, what colour is the wire presently connected to the oil switch?

Gerry

on my engine it has yellow/red wire going to oil switch. yellow/red wire goes to light capsule, black wire from capsule goes to ground. which makes me wonder if pink comes from module and splices into yellow/red wire, what does switch do? does it just change resistence in circuit? if so then my guess would be switch is closed when no oil pressure is present which would provide a ground to module to reduce engine rpm to 2000 rpm. cause it cant get a ground thru a light bulb. which means when switch has pressure it opens up its contact just allowing power to go thru light bulb to light up and find ground. basic path of least resistence i am thinking?? once switch closes and creates a ground for module, the yellow/red wire from light is meerly a high resistence ground wire wich causes light to extinguish?? i may be wrong but that is how i am thinking the circuit works...

 

[carholme]

Re: 1998 merc green oil pressure light--hows it work

Yet when you look at the parts list discounting the diode as that is for electric start:

Mercury, Mercruiser, Force, etc. - ELECTRICAL COMPONENTS - 9.9 /8(BONDENSEE) 4 STROKE

See item 10 pressure switch and where it goes through junction 47, it appears to be two separate circuits, where the wiring diagram shows the pink and yellow/red as joining together with a single yellow/red going to the light.

I will stick with it and see what else I can find. Trying to find a breakdown of the switch, 10 but that is proving difficult.

Gerry

 

[bamasteeler]

Re: 1998 merc green oil pressure light--hows it work

if you look at the end of harness(item 10) it has 2 connectors, my guess is that is where the pink wire from the module connects(item 47) and other connector on harness(item 10) connects to yellow/red wire of pilot light (item 30).