help me understand this instrument gauge...

[rdeeble]

i have a 76 and have taken out the instrument cluster to replace all the bulbs and I have come up with some mysteries on the fuel/temperature gauge.

First question... In looking at the fuel/temp gauge there is a contact terminal, in the back near where the handbrake light is, that isn't connected to anything (and no obvious dangling wire in my dash cavity). I'm stumped as to what is supposed to be connected here (see pic)?

Second question... in plugging this gauge back in and turning the ignition key to test the bulbs, my O light suddenly stopped working. It was initially working fine but while experimenting with different bulbs i put in a LED and it stopped working altogether. I put all the regular bulbs back, made sure none of them were burned - but still no O light. Could I have fry'd the circuitry with that LED?

thoughts anyone?

And while we are at it... why did the good folks at BMW label the flasher light "B" and the high beam light "F" ?

-rd

[JackBennett]

I only have the answer to the last 2... blinklicht und femlicht = turnsignal and highbeam.... Finally knowing German comes in handy!

[JackBennett]

And I'm not positive but I think my '76 had the same terminal on the back with nothing connected to it. I left it as such. Again, I'm not positive. Someone will no doubt have the esoteric knowledge of what it was or is for.

[rdeeble]

i knew i could count on you for that one Jack! thanks for the translation it makes my ocd a little easier.

now on to question one and two... anyone???

[aa/fd]

I don't recall having one on mine, but it resembles the tach connection on the right side of the cluster.

Maybe turn it over and follow the trace on the PCB see what it is linked to.

Common sense dictates it has some function or they (BMW) would not go to the expense of installing it.

[jgerock]

I think there was an earlier thread on the early vs. later dash clusters.

The wiring diagram would probably show the circuit (along with the tracer on the backside of the cluster board itself).

That set of terminals isn't on the earlier cars

For simpler folks:

"B" = blinker

"F" = flash (to pass)

[rdeeble]

for those of you following this thread jgerock is correct... this mystery came up earlier and some interesting threads that occurred can be found here:

http://www.bmw2002faq.com/component/option,com_forum/Itemid,50/page,viewtopic/p,614942/highlight,/#614942

http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,331384/highlight,early+later+clusters/

in one of the threads the answer to my question 1 seems to be provided by Curt Ingraham:

It's shown on the double secret wiring diagram for a US '75 2002. A brown/grey wire from the handbrake lever switch attaches to it, and that illuminates the "Brake" warning light in the cluster.

The Brake warning light is also turned on via a brown/blue wire in the 12-conductor instrument cluster connector from the brake fluid level switch on the reservoir cap.

The brown/grey wire also goes to the seat belt interlock brain. The diode in the instrument cluster blocks the low fluid signal from the seat belt interlock.

You can safely ground this extra terminal, and that will turn on the Brake warning light.

If you apply 12 volts to this extra terminal when the handbrake is applied, you will fry the handbrake switch or your 12 volt source.

_________________

Curt Ingraham

So for question 1... according to folks on the faq BMW made an additional terminal on 04 cars to meet US seatbelt requirements but discontinued this feature the following year on 75-76 cars probably because it was such a pain. The 75-76 models still had the additional terminal on the back of the fuel/temp gauge but they just were not hooked up.

Now on to question 2... i was a little worried i may have fried this part of the circuity with that bulb with backwards polarity or something. Turns out the oil sensor went kaput seconds after installing the cluster. Double checked the connection between sensor wire to the cluster by running a ground to the sensor wire. O light came on nice and bright. Made sure the switch wasn't suffering a grounding problem by running the same ground to the switch with sensor wire back on - no o light. Time to replace the sensor.

thanks to Curt Ingrahm for helping me trouble shoot this.