Topic

Like it says on the tin, the windows works when it wants to and doesn't work when it cant be bothered.

I have read a few places that it might be the replays in the BCU?

Is this likely?

Is it an easy swap

You need to find out what you have depending on your Vin as the systems are different, I know if you have an SCU they are soldered in.

Personally I would start by temporarily wiring a bulb in parallel with the window circuit so that next time it fails you can see if its the relay/ECU that is failing to provide an output or if its' the motor itself/ wring to the door.

If it is ONLY the passenger side window, I would check if the problem isn't with the switch. Swap the switches of both windows and see if it's now the driver side window acting up.

The first place I’d look is the switch, the contacts are probably filthy, I’ve written a how to on here somewhere….was quite a few years ago.

Passenger side window is controlled directly from the switch, the drivers side has relay control from the BCU because of its semi automatic operation. It will either be the switch, broken wires in the door where it hinges or the window regulator unit (motor) at fault. Switches are easiest to check and would be prime suspect.
Also the window regulators have a plastic bevelled drive gear that can wear, causing intermittent operation, but usually it goes down but not up when this occurs.

Sundance

Interestingly my passenger window has packed up whilst I was changing my brake pads.

It's not the switch - no difference when i swapped it for the drivers side.

It's not the motor - works when I applied 12 volts directly to the motor.

Is there a relay or a fuse I should be checking out please ?
Its a 2003 TF, different fusebox from that of the earlier TF and Mk2 F that I had just started to understand.

Yes, there is a window lift relay and two fuses. One under steering wheel fusebox and another under bonnet fusebox. Described here: https://www.the-t-bar.com/forum/roverlike-s-guides/97846-mg-f-tf-fuse-relay-listing

Thanks for the link. The fuses are fine but there is no power getting as far as the + feed to the passenger window switch. I've also swapped the relays around. Odd as there's very little to go wrong on the passenger side window and it was fine until I put the car on axle stands on friday to do the brake discs. Intriguing

BCU unit controls the relay which provides power to the passanger side switch. It prowides ground connection to relay when engine is started, or just contact given. By that relay coil is energized and you get power to the switch.

Thanks. It's odd for the BCU to suddenly stop sending a switched negative to the coil of the window lift relay for the passenger window but everything else to work ok including the more complex drivers side window.

Ive been looking at the wiring diagrams. The first thing that occurred to me was to run a permanent negative to the relay but Im assuming that would have the effect of keeping the relay permanently powered up as the other side of the relay coil looks to be an unswitched positive.
That would seem to leave the options of:

1. Find the BCU, check it's wiring connectors and if no obvious issue then open it up and check for defective solder joints. (Is this viable to open it up ?)

2. Remove the relay and bridge it's switch contacts so it is permanently applying power as far as the passenger window switch. ( I doubt this would be
detrimental to the car's security as someone would have to be inside to open the passenger window - and all they would be able to do is open the passenger window. )

3. run an unswitched negative to the window relay to replace the switched negative from the BCU. Then remove the existing live feed to the relay coil and replace this with a feed that is only live when the ignition is on.

Any thoughts on whether the BCU can be opened up non destructively please ?