Up's and down's of an electric window

This car had proved interesting, a flat battery combined with the wrong filament lamps in the brake lights meant it would not turn off with the key.


The reason the this Peugeot was booked in was a simple electric window fault.


Another garage had tried to find the fault but gave up. As the window would go down but not up they powered the motor from a 12v battery to send the window back up then disconnected the motor. This way the window could not be left stuck down.


As always it is the approach that is most important with any diagnostic job.


We always question the customer, this way we know what previous repairs have been carried out, thus the repair history.


In this case this proved very useful as we now know the motor works, even though it appears not to work at all.


Next we look at what does and doesn't work in this case the window can be controlled from the drivers door as well as the passenger door. So with the motor reconnected does it go down from both switches. Yes.

Looking at the wiring diagram which wire connects both switches and controls the current flow in the up direction?

I am left with two options I have colored these in Red and Blue, Red the power supply for the motor and Blue earth in the up direction.To prove which is at fault I need to prove a loss of continuity between the passenger window switch and the drivers switch.

Most people would use a multi-meter set to ohms or the diode test position. We prefer to use current measurement for this test as it is dynamic. That is to say the circuit is in use. We needed to test between terminal 1b and 3b using the meter as the wires as the amp setting gives the meter very little resistance. Then 4a and 2b.

Knowing this before going to the car and testing reduces diagnostic time. Understanding the circuit means it can be tested quickly. It may take a few minutes before you pick up the meter but it can save hours.

In this case the wire between 4a and 2b was proved to be open circuit. This method proves the diagnosis as with the meter set to amps in place the window worked in both directions from both switches. The task of finding location of the broken wire is more difficult but knowing it was makes running another wire the quicker solution.

Pugilistic Pug

This 306 came with a list of electrical problems, no big deal or so I thought.
The high priority job was enable the engine to stop on the key.
This is a safety critical repair, the first task was to get the engine started, the battery was completely discharged. A sure sign of the trouble ahead.
Once the engine started with a booster pack, you could remove the key and the thing kept running until you switched the lights on then off!
I fitted a replacement battery after cleaning all traces of electrolyte from the battery tray and surrounding areas. This restored the key to normal operation, but the side lights refused to switch off, plus the brake lights were on permanently.
The culprit, the brake switch had become dislodged. With the switch re-fitted and correctly adjusted we now had working brake lights, however the side lights came on every time the brakes were applied. I was beginning to think this was some sort of joke, but this is normally a simple case of incorrect filament lamps being fitted. Sure enough one of the brake light lamps was a single filament instead of a double filament, this back feeds the side light circuit putting the side lights on whenever the brake pedal is pressed.
The list of jobs was slowly reducing, but now I had to sort the passenger electric window. More on this next time.