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BF75A Oil pressure switch light fault

Cretster

Contributing Member
Hi


I have just rigged my engine and found the warning light for the oil pressure does not light up.


I have tested various parts of the circuit and I don't think this actually relates to bad oil pressure at all. The light does not come on when the ignition is on but engine not running, and I think it should be, so this would presumably rule out an actual pressure fault.


I have found that inside the remote control box (R Type), there are 4 wires to the warning lights:


Red (Temp signal?)
Yellow (Oil pressure signal?)
Black (earth)
Black/Yellow, and Grey combined (12v+)


If the yellow wire is disconnected then the oil light comes on with the ignition, but if I connect the wire then the light goes out.
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I have traced the wiring harness back to the engine and all the wires in the main harness have good continuity.


The yellow wire terminates at the oil pressure sensor on the engine block, and appears to have continuity to earth when tested. I have a spare engine and the sensor on that behaves the same way.


I think this is normal, so I would have to therefore assume that the yellow wire is the earth feed to the oil warning light and SHOULD have continuity to earth since the light is meant to remain on. So the fault is not the switch.


So what do I need to look at? I can't think why connecting this would cause the light to go out, so any help in troubleshooting this would be much appreciated.


Thanks!
 
So what was the answer? Post it here for someone searching the archives that may have a similar issue.
Thanks.
 
A bit of poor connection causing intermittent light activity, but when I was surmising about the functionality of the bulb I had some of my rationale back to front about the light being on with ignition on & engine off etc.

One of the warning light modules is junk as well but I have a good one in now. Rubbish LEDs though - you can barely see them in bright sunlight!!
 
So, to summarize then, you are saying that the green oil light comes on and stays on when the engine is running, correct? If so, that is like all the other Hondas.

A trick I've used before is to glue a short length of jumbo drink straw, painted black or dark blue, over the light to concentrate the beam a bit better and to also block it from illuminating the area when running at night.
 
It doesn't come on with just the ignition (and I realise you weren't suggesting that, but I'm just saying for clarity for others), but yes, once the engine starts running the light comes on and stays on.

Thanks for the tip. If it wasn't for the warning light module being completely sealed with resin, I'd break it open and fit a decent quality LED in there so it's really obvious.
If I knew exactly what each of the 4 wires going in was connected to then I'd crack open one and do this, then seal it back up again.
The wiring diagrams give the colours of the wires but don't say what they're actually connecting to inside the module.
 
I have NEVER let a little plastic box stop me from going in there and wrecking everything. That's why my nickname is DREMEL MADMAN! Thanks for the clarification.
 
No worries!

I suppose I ought to at least try that, since I'm usually the same in terms of hacking things to bits like that.
Even so, it looks a pretty tedious thing to try and get into. I've got 3 control boxes and am using one engine, plus one of the warning light modules doesn't appear to work, so there's no harm in trying it I guess.

It's 12v to it but whether that's a 12v LED, or smaller one with resistor I don't know.
It really is dim though.

Speaking to my engine guru yesterday he said he's changed a ridiculous number of those light modules over the years. I think he said they're about £80, which takes the p1ss. A cubic inch of plastic with 2 LEDs in it for £80!!

Have got some ultrabright 12v LEDs I think so I might attack this over the weekend if I get bored or if it's raining!
 
I imagine that the wire carrying 12v going in to the module terminates at a PC board for the LED. LED's by nature can't handle much more than around 3vdc and must have a resistor to drop the voltage. I would guess that your 12v LED's have a resistor built in to the housing and would be a bit larger than the ones in the module.

At any rate, I have never really liked the Honda green oil lite approach for informing the helmsman. No one ever really pays much attention to that light while operating the boat and, on tiller steer outboards, the light is always BEHIND you when you're running.

And, I absolutely DO NOT appreciate ANY additional lights in the cabin or cockpit at night! That incessant green light burning in my eyes on a long night run would make me get out the black electrical tape and shut it up!

But, I guess they had to do something so that when you brought the thing in with a seized engine because the oil went low they could say "we tried to warn you"!
 
The 12v LEDs are typically no different visibly from the lower voltage 2v, 3v, or 5v ones I've got so I'm not sure quite how that works to be honest.

Maybe it's like you say that a really bright LED would be a distraction in low light or darkness. You'd think red would be better though if anything as it's easier on the eyes in the dark.

I did think it was a bit stupid to have a light that should be on all the time, rather than one that only comes on when there's a fault but they must have their reasons.
Aside from anything else, the buzzer is meant to sound and the engine go into limp mode if there's an issue, so the lights are really a secondary thing to tell you whether the fault is water temp or oil pressure related once you already run into trouble.
 
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