Electrical weirdness

[DaveP]

Hi all,

I have two totally separate issues on two different cars but wonder if the collective experience have any knowledge that may help ?

1) a friend has a 2.0 1999 roadster and finds that his electric windows work normally but when he puts his lights on they stop completely. All it takes is sidelights. Anyone seen this before ?

2) on my Kobra I have fitted a replacement dashboard and in doing this replaced the switches. My issue is that I have fitted a rear foglight switch and when I switch on my rear foglights it works fine. But when I switch it off the foglights stay on. Extra info is that the switch itself illuminates (mot requirement) and that the rear foglights themselves are LEDs. Now the thing that has changed is the switch as I have had the led rear fogs for 3 years and they worked correctly before. Any obvious thoughts? I will have to take a look under dash and confirm wiring detail if needed. Oh mine is a 2001 2.2

Thanks all for reading this and any input.

Dave

 

[Synclare]

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[DaveP]

Thanks for the view. Must be something around that. The switch is illuminated when on so we have a wire to earth for that. Also the LEDs have no real load resistance which confuses things too. They did work ok before so may be a red herring.
Will get to bottom of it eventually

 

[Rudyrov]

Could be the illumination is bleeding through?
Try disconnecting the illumination and eliminate that possibility.

 

[Mike Fishwick]

Once an LED has been turned on and off, in some cases it can receive enough power to remain on from a magnetic field generated in the adjacent wiring. I would fit a temporary slave wire from the switch to the lamp (via the relay if fitted) and see what happens.

The window/lights problem sounds like a voltage drop caused by the window motor, due to a high-resistance connection, combining with a common wiring junction with the lights. There is no 'silver bullet' for this lind of fault - you will have to look at the wiring diagram and try to find a common point.

 

[NZ00Z3]

Without seeing your fog light wiring diagram, it's really hard to say what it is.

LED's do not require a lot of energy to work, once they are on. A very minor back-feed will keep them on. You can use a diode to block back feeds.

 

[jaguartvr]

Gookah's your man. Lots of problems working out my wiring on the 250's and he solved every one for me. It sounds like you have the same switch for the fogs as I have but I haven't fitted it yet. I'll wait until you have sorted it out first!
Gookah gave me a wiring diagram for the CBS hazzard switch which is in the rebody section.

 

[DaveP]

Only guessing on the foglights issue but presumably the relay is staying energised. I think the original switch does not stay pressed (latched) in when operated and a second press de-energises the relay. Your new switch presumably is not energising/de-energising in the same fashion.

So the latest on this one is that I gave @Synclare's response a little thought and realised that he may have hit the nail on the head?

So I tried just that. I turned the lights on via (I have fitted the original) normal light switch. Turned on rear fogs and they work fine. I get a nice lil LED on the end of the toggle switch light up. When I then switch the toggle off I lose the LED but the rear fogs stay on. Now if I repeat the operation (switch toggle back on and off just like the original switch) then they do go off. Thus the second press needed to de-energise the relay must be all that is required. I am happy with this approach as it is merely an operation needed. I could swap out the toggle for an on - off momentary but then need to install another tell-tale for rear fogs in the dash,which is all in place and covered in vinyl and I don't have an obvious place for it.

When it comes to MOT time I will explain the operation and show tell-tales to the tester. I have to show him each year where the horn button is in any-case.

Thanks @Synclare - I was going to have to follow a more complex route if I hadn't tried this. Thanks for all other suggestions and support too.

On to issue 1) helping out a FB 'friend'.

Dave

 

[DaveP]

to point 1)

the main point where I can see a commonality is on the switches themselves.



The diagram shows that the switches illuminate when lights are on. I am unsure as to how to read the switch diag accurately as I understand it is a 5 pole switch but not sure, except for powering the bulb in the switch, the extra feed would do to break this. I am talking a stock Z3 in this scenario not my wiring naughtiness in my kobra.

? Dave