Can anyone tell me why this dashboard button interrupts the circuit for my electric windows

[Kalimsnor]

So I have a button in me E30 dashboard with no label (part nr. 1370724 - http://www.bmw-etk.info/parts-catalog/p ... 1311370724) which stops the windows from working when engaged. Is it perhaps to safe the battery?

[minesapint]

The electric window lifts are protected against faults and overloading by an automatic circuit breaker and fuse.
The electric window lifts can be switched off with the automatic circuit breaker, to prevent say children left in the car from operating the windows and perhaps injuring themselves.

[Kalimsnor]

The electric window lifts are protected against faults and overloading by an automatic circuit breaker and fuse.
The electric window lifts can be switched off with the automatic circuit breaker, to prevent say children left in the car from operating the windows and perhaps injuring themselves.

Thanks!

[Kalimsnor]

So I connected the two cables directly a few days ago, and now I suddenly had a dead battery. I assume this is related but I'm quite confused as to why this happens. Any ideas?

[Ukhozi]

To answer the OP, that is correct, it is supposed to. RTFM

Do NOT mess with electrics unless you are certain what you are doing and NEVER join wires from a unit as a bypass. The switch is a window safety lockout as said above. and seems to be doing what it should.

[Kalimsnor]

To answer the OP, that is correct, it is supposed to. RTFM

Do NOT mess with electrics unless you are certain what you are doing and NEVER join wires from a unit as a bypass. The switch is a window safety lockout as said above. and seems to be doing what it should.

I am aware it is safety lockout. Now I've turned it into an antitheft button, but it seems as if something is draining my battery now. Hence my question.

[ChrisHC]

The point is that button is a circuit breaker protecting the window motor circuits. If you have taken it out of the circuit by joining the cables leading to it directly, you no longer have a circuit breaker protecting the window motor circuits so if a fault develops such as a short circuit the current will continue to flow and flatten the battery if it does not burn out part of the wiring first. Therefore it should be re-connected.

If you have used it for some sort of anti-theft arrangement as you say, that may be where the battery drain is coming from. The most likely suspect in any fault finding is the last thing you worked on!

[Brianmoooore]

The closest I have ever come to burning an E30 and my workshop was when something heavy fell onto one of the window buttons overnight on an E30 that had electric windows fitted with no circuit breaker and a permanent live supply. The loom and window motor were burnt out in the morning, the battery flat, and the whole place filled with acrid smoke.
The fuse will not blow and offers no protection for a stalled motor.

[Kalimsnor]

I am *very* convinced and put it all back together as it was. I'll purchase a new button and hide it somewhere to interrupt the fuel pump. Thanks everyone!

[Tzantushka]

I am *very* convinced and put it all back together as it was. I'll purchase a new button and hide it somewhere to interrupt the fuel pump. Thanks everyone!

Good.
We only have your interests at heart.
No one likes to see an E30 inadvertently sacrificed because of some well meaning mods.

If you're looking for an OE looking button, from memory the fog light switches fit in the switch blanks.
IIRC, there's the 2 button version for front and rear fogs and a single button for the rear only.
That could be an option.

[Kalimsnor]

I am *very* convinced and put it all back together as it was. I'll purchase a new button and hide it somewhere to interrupt the fuel pump. Thanks everyone!

Good.
We only have your interests at heart.
No one likes to see an E30 inadvertently sacrificed because of some well meaning mods.

If you're looking for an OE looking button, from memory the fog light switches fit in the switch blanks.
IIRC, there's the 2 button version for front and rear fogs and a single button for the rear only.
That could be an option.

That's actually a really nice idea. I was thinking of hiding it under my chair, but this is far more clever!

[Banban3]

Are you interrupting the fuel pump using a relay, or directly cutting one of its wires through the switch?

I did the first option, which allowed me to hide somewhere a very small lever switch that controls a relay. This relay then closes the circuit for the pump.

You can get a signal for the relay from the options plug (the white one, passenger side if I am correct). There is the pin F that delivers 12V in START and RUN. I have used this one as the signal to close the additional relay. The micro switch is located between this pin and the relay.

The reason I ask is that if someone gets into your car and notices two switches for the fog lights, that may catch his attention. With a hidden micro switch, which you can place anywhere in the car, + how dense is the loom of the car, I feel safer.

[Brianmoooore]

Are you interrupting the fuel pump using a relay, or directly cutting one of its wires through the switch?

I did the first option, which allowed me to hide somewhere a very small lever switch that controls a relay. This relay then closes the circuit for the pump.

You can get a signal for the relay from the options plug (the white one, passenger side if I am correct). There is the pin F that delivers 12V in START and RUN. I have used this one as the signal to close the additional relay. The micro switch is located between this pin and the relay.

The reason I ask is that if someone gets into your car and notices two switches for the fog lights, that may catch his attention. With a hidden micro switch, which you can place anywhere in the car, + how dense is the loom of the car, I feel safer.

Interrupting the pump supply is relatively easy for someone that realises what is happening to bypass. You need to arrange the switch to SHORT CIRCUIT the pump supply, which will pop fuse 11.
No one is going to notice an extra switch on an E30 panel, especially if you put the pump switch in place of one of the existing ones and relocate the original. Can't see the point of complicating things with a relay at all.

[Banban3]

No one is going to notice an extra switch on an E30 panel, especially if you put the pump switch in place of one of the existing ones and relocate the original. Can't see the point of complicating things with a relay at all.

Well, that's the question I don't have an answer to (and which led me to do what I did): how would you relocate an original (hence big) switch except in one of the spaces that was made for it? And if so, then I tend to think (personal opinion here) two identical switches may somehow catch someone's attention, not to mention they are easy to pop out for a check. Otherwise, you may relocate the original switch somewhere else, but then you'd have to find the appropriate space. Hence what I did: I only had to find a tiny place for a small switch where to hide it to and make it hardly noticeable, and I tend to think, maybe wrongly, that it is an easier task.

Then the reason for the relay is that cutting the pump supply wire would have needed a bigger switch, harder to hide.

I do understand the interest to short circuit the pump live wire with the switch and never thought or heard of that before. I'll keep it in mind, if some day I do the same, then I guess I'b blow a decent number of fuses before getting used to it. But wouldn't bypassing it be the same easy task as with my switch? 12V supply on the pump, and there it goes:?:

Anyway: if someone wants to get away with your car, they will eventually. Whatever the means, let's just make this task as long and hard as possible to discourage them as much as possible. Just wanted to suggest another solution.

[Banban3]

No one is going to notice an extra switch on an E30 panel, especially if you put the pump switch in place of one of the existing ones and relocate the original. Can't see the point of complicating things with a relay at all.

Well, that's the question I don't have an answer to (and which led me to do what I did): how would you relocate an original (hence big) switch except in one of the spaces that was made for it? And if so, then I tend to think (personal opinion here) two identical switches may somehow catch someone's attention, not to mention they are easy to pop out for a check. Otherwise, you may relocate the original switch somewhere else, but then you'd have to find the appropriate space. Hence what I did: I only had to find a tiny place for a small switch where to hide it to and make it hardly noticeable, and I tend to think, maybe wrongly, that it is an easier task.

Then the reason for the relay is that cutting the pump supply wire would have needed a bigger switch, harder to hide.

I do understand the interest to short circuit the pump live wire with the switch and never thought or heard of that before. I'll keep it in mind, if some day I do the same, then I guess I'b blow a decent number of fuses before getting used to it. But wouldn't bypassing it be the same easy task as with my switch? 12V supply on the pump, and there it goes:?:

Anyway: if someone wants to get away with your car, they will eventually. Whatever the means, let's just make this task as long and hard as possible to discourage them as much as possible. Just wanted to suggest another solution.

[flybynite]

But wouldn't bypassing it be the same easy task as with my switch? 12V supply on the pump, and there it goes:?:

No that is not how it would work.

Because you don't know it the thief would probably not know it either and that is why it might work.

[Tzantushka]

The good thing with the OE switches is they look, well... OE and fit in multiple places (and don't look out of place).

If you don't have AC then there's another switch blank.
The 2 button fog light switch looks right at home in that position as part of the HVAC control.

Yes, that will stand out to an 30 aficionado.
But less so to an opportunistic thief who is operating under time pressure.

As Banban said if someone really wants to steal your car they will. Eventually.

[Banban3]

But wouldn't bypassing it be the same easy task as with my switch? 12V supply on the pump, and there it goes:?:

No that is not how it would work.

Because you don't know it the thief would probably not know it either and that is why it might work.

Not sure I get what you mean, but maybe because I was not so clear. I think I have fully understood what Brian described when saying to short circuit the pump, any voltage applied to the pump while keeping the connector in place would not trigger the pump for sure due to the short.

What I meant with the 12V supply is that if I unplug the pump connector, and put the + from a 12V battery (like the car's one) directly on the pump and the - to the chassis, it will work hence provide fuel to the engine. The key is to remove the connector from the pump, to make it independent, isn't it all?

Or am I getting something wrong?

[flybynite]

. The key is to remove the connector from the pump, to make it independent, isn't it all?

Yes, and anyone thinking of taking an E30 will read your explanation on this open forum and know what to do so probably not worth doing any of it

[Brianmoooore]

One of the things I always carry in my car is a three metre or so length of wire with a croc. clip on each end. If I was 'appropriating' your car, and realised the fuel pump wasn't working, I'd flip up the rear seat cushion and attempt to jump power in at the wiring to the plug and socket on the RH side. Hammering the croc clip jaws through the wires insulation would do and take seconds. If my shorting switch was in place, all I'd get is a very hot length of wire and/or another blown fuse depending on where I was getting the power from. If there was just an isolation switch on the supply, my wire jump would work, and I'd be on my way.
What I wouldn't be hanging around to do, unless I was absolutely certain that I wouldn't be discovered, is removing the cover over the pump, unplugging it and connecting both an earth and a supply.

[Banban3]

Well, the way I have wired my relay and isolation switch, you need to remove the cover to get the pump working. Trying to feed the pump as described above from the socket under the rear seat will not work.

Again, making things as hard as possible.

[Ukhozi]

As a qualified security installer, (Cobra, Philips, Serpi-Star, Gemini, Moss and Tracker) I have NEVER had a car stolen, some were messed up a bit by people TRYING but failed. and that's for Mod special projects from 1987 to 1989 and from 1989 to 1999 with my own company and a few since.
Installation is the key to any good alarm, I even had to disable the immobilizer on Mr Vladimir Putin's vehicle after it failed, (yes, THAT Mr, V. Putin, when he was in Marbella)., it was easy despite being all black leads as it was all connected under the steering column and not integrated into the system as such.
A simple interrupt, (breaking the feed or earth) on a pump or any circuit is easy but do not do it in an obvious place.