SOLVED - best process to identify electrical problem?

[Devilish_02]

Got home last night and turned off the car. Pushed knob in to turnoff headlights. Headlights turned off but dashboard light* stayed on. The light can dim until there is no light, but not an ideal solution. Guessing the issue is at the point where the electricity is cut off from the dashboard light. I phrase it that way because I have no experience working with electronic systems. 

 

My questions is, if you didn't have BMW2002faq, how would you go about identifying the problem?  Would also love the answer or suggestions, but want to learn how my car works and how to fix it while....you know.....fix it. 

 

Thanks in advance,

Jake 

 

* Bonus points if you head Meatloaf signing about dashboard lights while reading this post. 

Edited November 11, 2022 by Devilish_02

[John76]

1 hour ago, Devilish_02 said:

how would you go about identifying the problem?

Welcome Jake.

 

First...get on this BMW2002faq forum!

Second: Tell us about your car (year, model, mods, etc.)

Third: Explain the best you can what issues you are having, when they started, what changed, etc.

Then stay connected to this forum until your problem(s) (relating to your 2002) are solved.

Lots of talent and help available!

 

John

[tzei]

A/B testing.

 

Change only one variable at a time to narrow down & identifying the problem. So try with known good light switch if it cures the problem.

 

Can you fix the light switch? Maybe, maybe not. Those are tricky little buggers.

Edited November 9, 2022 by tzei
Typo

[gruizer]

An old hot rodder once told me "90% of your electrical problems are related to a bad ground".  I have found this to be true 60% of the time - everytime!

 

[Mike Self]

My (somewhat) educated guess is that the variable resistor that controls the dash lights' brightness has run amok.   It's inside the headlight switch, and is nothing more than a resistance wire wound around an insulator.  Turning the light switch knob moves a contact around this resistance wire, varying the voltage going to the dash lights.  When those switches get old, they get cranky, and my guess is that somewhere inside the switch either the resistance wire or the movable contact are boogered up, and  are not allowing the dash lights to disconnect.  The light circuit on an 02 is live all the time (except the headlights on 71 and later cars) so the feed to the switch is hot all the time.  

 

Best way to check:  find another switch and substitute.  You might also try cleaning that variable resistor with tuner cleaner or even brake cleaner and see if that helps.  But my guess is that the switch is going bad and probably can't be fixed.  

 

let us know whatcha find...

 

mike

[Devilish_02]

Thanks for all the input. 

 

As noted above, it was probably the light switch. 

 

Photo of what the variable resistor looks like. Second photo shows two tiny springs, one of which is somewhere in my garage. 🤬 Thus, going to purchase a replacement vs trying to fix. There is another thread where people discuss successfully repairing them. Not losing tiny springs being a lynchpin for success. 

 

Thanks!

Jake

 

[AustrianVespaGuy]

Answer

On 11/9/2022 at 2:32 PM, Devilish_02 said:

My questions is, if you didn't have BMW2002faq, how would you go about identifying the problem?

Wiring diagrams!  Basically for any electrical problem, you need the diagram for how the circuit works, and from there you can move on to various tests to isolate/identify the part of the circuit that isn't working, and then fix it.  Let's say you have an early Euro 2002, so that diagram would be here:

https://www.2002tii.org/diagrams/bmw2002-early-euro.pdf

You find the light switch on it, the bubble 21, and you see that the rheostat for the dash lights gets powered by the Green/Red wire from fuse #2, and then drops the voltage through the rheostat (for the dimming), and then goes to the dashboard on the green yellow wire:

So then you just start checking the voltage at wires and working your way backwards from the lights toward the battery until you find the problem!

[Mike Self]

11 hours ago, Devilish_02 said:

There is another thread where people discuss successfully repairing them. Not losing tiny springs being a lynchpin for success. 

Betcha a cut down ballpoint pen spring will work for the missing one...  cheaper than a new switch!

 

mike

[Devilish_02]

@AustrianVespaGuy thanks for the explainer! 

 

@Mike Self the one I need is still significantly smaller than that but it is a good idea. 

[HBChris]

I’ve never found a reason to dim the dash lights in my vintage BMWs.  Just jump the two wires together and bypass the rheostat.