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John Brown · Joined: 07 Nov 2002 Posts: 903 Location: Leesburg VA

US spec in this case. Anybody agree with the that the diode - shown in the circuit which ends up running to the oil pressure sending unit - is only to provide a path the ground for testing of the operation of the light with key on and no oil pressure?

Which begs the question - does the oil pressure sending unit provide a physical ground for the warning light though the case? (There is not an actual connection indicated - but otherwise I'm led to believe the ground is back up the 'G' line and that is just silly).
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John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

Smoothie · Posted: Tue Jan 30, 2007 2:53 pm Post subject:

No, the oil pressure light gets power via ignition switch 15 and terminal 7 shown at the left of the instrument cluster rectangle, so that diode and the wire after it aren't needed to test the light at startup, it always has 12V+ available anyway as long as the ignition is switched on. -So switch on ignition, oil pressure sender sees zero pressure because engine's not running yet, oil light comes on, powered by 12V+ from the igntion switch.
Yes, looking at Haynes pg. 296 and the oil pressure sending unit, it grounds through the threaded connection to the engine (vertical line down to "9"). "G" is a variable resistance to the gauge needle and "Wk" grounds that bl/bk wire that runs (tracing it backwards) through C12-D18-6- then the warning light - obviously this turns on the light when the sending unit closes its' switch, completing the ground through its' threads.
Then looking back at D18 and tracing the other bl/bk wire branch to the left and ultimately to "Öl" of the brake warning light, apparently that diode's there to keep the oil pressure light circuit from grounding through the brake warning light assembly, then either the brake fluid level switch or the parking brake contact switch when either is closed. "[IV 8]K" is at 12V+ whenever the ignition is switched on, so apparently that left brake warning light illuminates both when either the brake fluid level switch or the parking brake contact switch is closed and when the oil pressure sender units' switch closes to complete the ground there (so when the oil pressure light illuminates, you should also see a brake warning light - maybe in this case, instead of telling you there's a problem with the brakes, they're trying to tell you to brake because you have no oil pressure? -I don't know..). The right-side brake warning light illuminates when its' ground is completed apparently through "L" of the seat belt warning relay (, so now they're telling you to brake because you don't have your seatbelt on

). (

, but possible - who among us can claim to fully understand the workings of a German automakers' mind?

)

Long story short: If that diode weren't there, then the oil pressure warning would illuminate whenever either the brake fluid level switch or the parking brake contact switch were closed.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

One as the car was designed, and one to comply with USDOT?
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

USDOT requires two parking brake warnings...?
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1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Smoothie · Posted: Wed Jan 31, 2007 3:21 am Post subject:

FMCSA - Federal Motor Carrier Safety Administration - Another government agency I'd never heard of. ..I'll presume they're not wasting toooo much of the taxpayers' money.

If you like reading -
http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.asp?section=571.105#
Scroll down to "S5.3 Brake system indicator lamp." - those would be current regs though.

Looks like someone completed the horn section in about 10 seconds on their way out to lunch

- http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/393.81.htm
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

!tom · Posted: Wed Jan 31, 2007 8:44 am Post subject:

Hmmm. S5.1 indicates the need for automatically adjusting service brakes. Looks like most of us are out of luck on that one!
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78 924 NA
5-lug

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

For your sakes I hope the Feds aren't monitoring this board!
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1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Smoothie · Posted: Thu Feb 01, 2007 2:17 am Post subject:

Actually, I noticed that FMCSA is for busses and large trucks. "Motor Carrier" should have been a hint..
I tried searching the Bureau of Miscellaneous Information <click>, but have had no luck finding the equivalent information for smaller vehicles.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox