Brain Trust Help needed on Parking Brake Light, Parking Brake Light Always on...... Options

[Gatornapper]

Once again need the help of the great 914 Brain Trust here........

My Parking Brake Light stays on all the time.

The switch is fairly new and it is functioning properly.

Disconnecting the brown (ground) wire to the switch, it has no continuity or resistance to ground. So it is not "grounded out" somewhere.

I see in my great 914 electrical schematic of the ground circuit for the switch and light that there are two diodes in the circuit.

I am guessing that one of them failed.

Can anyone tell me where these two diodes are located?

Or where else the problem might be?

As always,

TIA,

GN

[Literati914]

I’d say ‘don’t be surprised if there is no reset button to push’ … I have 3 old 914 master cylinders and none of them have a reset button. Am I missing something? They all have some type of a square plastic “tower” where the spade(s) are … is that somehow the reset “button”? I lightly tried prying the plastic block off on one and that didn’t seem to be the case (IMG:style_emoticons/default/confused24.gif)

Not all switches have the latching function and the reset button. The later model two pole switches are not latching - when there is a problem in the master cylinder the pressure differential between the hydraulic circuits will cause the light to turn on.

If you’ve converted from an early single pole to double pole switch (or vice versa) it needs to be wired accordingly.

My car came with a separate ground wire at the MC input - this is the only reason I switched from the single pole unit (which has an obvious button to push) during installation, besides already having one on hand.

So, as for the single pole switches like I posted above and you posted in the other thread (showing MC internal workings) - how do they get reset?

[Superhawk996]

I’d say ‘don’t be surprised if there is no reset button to push’ … I have 3 old 914 master cylinders and none of them have a reset button. Am I missing something? They all have some type of a square plastic “tower” where the spade(s) are … is that somehow the reset “button”? I lightly tried prying the plastic block off on one and that didn’t seem to be the case (IMG:style_emoticons/default/confused24.gif)

Not all switches have the latching function and the reset button. The later model two pole switches are not latching - when there is a problem in the master cylinder the pressure differential between the hydraulic circuits will cause the light to turn on.

If you’ve converted from an early single pole to double pole switch (or vice versa) it needs to be wired accordingly.

My car came with a separate ground wire at the MC input - this is the only reason I switched from the single pole unit (which has an obvious button to push) during installation, besides already having one on hand.

So, as for the single pole switches like I posted above and you posted in the other thread (showing MC internal workings) - how do they get reset?

@literati914

Bear with me I’m not trying to be an (IMG:style_emoticons/default/bootyshake.gif)

Push the button!

Having said that, not all single pole switches have the button. This means they are non-latching and will “reset” themselves (like the 2 pole switches) when the underlying pressure imbalance within the master cylinder is corrected.

Here’s the thing - these are 50 year old cars that have been (IMG:style_emoticons/default/sheeplove.gif) for decades. It’s not possible to tell exactly what you have. There were so many variations on these switches across OEMs (and now the Chinese aftermarket (IMG:style_emoticons/default/headbang.gif) ) it’s hard to say exactly what you have. At some point, you’re going to have to use a DMM to understand what switch you have and to troubleshoot your particular car - including the wiring.

In an effort to be helpful - again not trying to be an ass but I know I come off that way, it isn’t my intent. (IMG:style_emoticons/default/beerchug.gif)

Here is the pic you posted:
Single pole - no reset switch installed in master (none)

Single pole, new looking — appears to have reset but you’ll need to test with DMM (circled). You likely need to remove the black nipple or cover depending on how solid that cover is. That should expose the reset button assuming that is what’s there.



Here are other examples:


I’ve seen that button also be red, and a faded red that looks brown.

Here’s another that looks modern and like what you posted. picture came from one of the Euro parts sites.



The one I posted is a single pole non latching switch - the same as the switch shown in one of your master cylinders marked as “none”.



A DMM is your friend when working with an unknown. Play with the switch in hand to understand what you have and to see how it’s working.