LED oil pressure light

[montmil]

Was getting outta the heat late this morning after tooling around on the R65; just chilling at RadioShack and getting ideas for projects. When asked if I needed help, I told the young clerk, "No thanks. Just doing some casual shoplifting." They never know if they should laugh or follow you around. I like the attention.  

And what did I discover but a clever little LED that I could use to develop an oil pressure warning light that would fit in with my "less is best for my Beemer" project. Plus, it'll get Justin off my case -at least for a few days.



Here's a neat 12 volt LED assembly w/resistor, red lens, a thin lock nut and only $1.99. I added the thin aluminum washer.



Now then. Where can I put this where it will be noticeable as a warning light, safe from harm and not look too tacky? Well, D'Oh! How about that hex-shaped opening there on top of the fork stem? Maybe I could find a replacement nut in all my junk jars that would fit both the LED stem and be a sorta press fit into the stem opening.



Found one! I had to add a thin aluminum washer under the LED to help the fit and finish.



Re-routed the lead from the oil pressure warning switch. It now goes forward rather than back and up into the OE wiring harness. Added a ground wire from the LED to chassis earth. Have insulated spade connectors to ease removal of the LED unit for front end work, if required. Dilectric grease be good.

Hope that sucker never lights up!  [smiley=thumbsup.gif]

[Jon_P]

very cool, and it doesnt scream hey look at me i look out of place from the cool looking gauge.

[Justin B.]

You had better hope it does when you turn the key on!  I guess I'll have to find something else to gripe about - rat...

[Rob Valdez 79 R65]

*Does* it light up when you turn the ignition on?  :-?

[montmil]

*Does* it light up when you turn the ignition on?  :-?

Wife came home. Supper time. Awful hot in the shop. Will "turn on" tomorrow.

So, for reference... Is this light supposed to be like with my VW Cabriolet? When I wind it up, the O/P light comes on until the engine stabilizes -maybe 1-2 seconds- and away we go.

I never saw the light lit on the R65 while I had the ugly "bean pod cluster" OEM instrumentation. Bad sender? Or maybe I wasn't paying attention. What's "normal" ops.

And I do not have a keyed ignition switch. A 30-amp rated, sorta hidden, weatherproof toggle handles that chore. The original -to me- keyed ignition switch was some bastardized Rice switch. Keihn (?) by name. Wired up weird.

[Justin B.]

If you never saw it come on then something was not right.  It should be on as soon as you turn on the key and extinguish pretty much immediately after starting.  If it doesn't then troubleshoot the circuit back to the pressure switch.

[montmil]

If you never saw it come on then something was not right.  It should be on as soon as you turn on the key and extinguish pretty much immediately after starting.  If it doesn't then troubleshoot the circuit back to the pressure switch.

Roger that! I went through the wiring diagram in Clymer's and noticed the circuitry in the tach's printed circuit board. Opened up the tach and... gawd! Way too much to deal with.

I did try tapping into the GEN light mod package I purchased from Rick at Motoraad Elektric. His resistor circuit bypasses the tach's circuitry. Still no joy.

I plan to contact Rick and get his ideas but I'm also suspect of the oil pressure sender switch. When I purchased the bike, the OP light never did "light". The bulb tested as functional.

For now, I've yanked the whole deal out. An idea that, for now, doesn't work.

[Rob Valdez 79 R65]

Just a layman's guess here, but I think the oil pressure circuit is pretty "dumb".  I don't see it needing any of the electronics in the tach to perform it's function.  It is just that that is where the oil warning light resides.

If you have not seen a light before starting the engine, that is not a good thing.  Your butt is not covered.

[Justin B.]

Rob's correct, just the same 12v source that feeds the charge and neutral lights, the light, some wire, and the switch.  When oil pressure is below X the switch is closed providing a ground to the idiot light...

[montmil]

Rob's correct, just the same 12v source that feeds the charge and neutral lights, the light, some wire, and the switch.  When oil pressure is below X the switch is closed providing a ground to the idiot light...

That was my thinking, too. However, the wiring diagram shows the two leads from the OP warning light; one direct to the sender and the other goes to a "diode" that resides, according to the diagram, inside the tach body. A green with blue tracer. Also tied into the GEN warning lamp and the Neutral lamp. Then, they all go to that square with the word "diode" inside it and on towards various switches and senders. Almost Italian in its complexity!

The LED works. Circuit is secure except for the lingering question: Is the OP sender functional? As it's a metric stud and hole in the crankcase, I may invest in a new VW sender and give it another test. Then again... maybe not.  

[montmil]

...Your butt is not covered.

I got my Jockeys on! "Hey, Michael. I'm wearing your underwear." ...if you've seen the TV commercial

[Justin B.]

If you trace the entire diagram you will see that the switched 12v gets to those 3 lights before the diode.  The diode I know of is in the neutral light circuit to prevent interaction between the neutral switch and clutch lever switch.  Easy to test the switch, disconnect wire and hook meter from terminal to ground - should read low (almost zero) ohms with engine off and open with engine started.  The correct sub for the switch is from something like a mid 70s to 80 BMW car, the air-cooled VW switch is the wrong thread.

[montmil]

Time to warm up my DVOM!

I'm back. With engine off, OP switch lead disconnected and DVOM leads from switch to ground = 00.3
With engine running... No reading at all. Nada. Nuttin' honey.

Looks like an early morning ride to NAPA for, what? Mid 70's-80 BMW automobile OP sender. Maybe that'll get it right. No wonder I had no OP light even with the original bean pod instrument cluster.

[Bob_Roller]

Monte,

If you still have the round electrical connector that plugged into the tachometer still attached to the wiring, the brown with white spiral band is the wire to the oil pressure switch.

Connect a switched 12 vdc positive power source to one lead of the LED, and the other lead of the LED to the brown/white wire, and it should work, as long as the oil pressure switch is functional.

The oil pressure switch has power to it anytime the key is in the ON position, and it gets a ground to complete circuit when there is no oil pressure, and opens when the pressure comes up to 3-5 psi , or so.


On the subject of the diode in the tachometer, that is an engine over speed indication LED on the '79 model bikes.

I posted the previous reply before seeing your test results, with the engine shut off, you should have low resistance, usually under 1 ohm, with the engine running, the switch should be open, infinite resistance, so it looks like your pressure switch seems to be working.

[Rob Valdez 79 R65]

You might want to take your switch with you when you go to the store.
BMW used two different switches.  It was the thread pitch that set them apart.