TF Drivers Window Opens Itself In The Rain

Hi, I have a very interesting problem and not sure where to start. My son had a lovely TF which found some black ice, and lost an argument with a roadside railing, so ended up being no more. We have now purchased a replacement, which is a 2005 with 49K on the clock. However, it is nowhere near as good as the one he had previously. It may have a HG failure which is being addressed, it has some bodywork issues which are being addressed, a P0170 code (possibly related to HG failure, or blowing exhaust) being addressed, and has a very interesting electrical fault.

Sometimes when he is using the car in the rain, the alternator light flashes once, and the drivers window opens on it's own. This is intermittent, and may not happen, and then today happened twice in a 300 yard movement of the car. Obviously this window is being activated, though not sure from where. I am assuming that water is shorting something out somewhere, but where I have no idea.

Has anybody seen this before, or is this a new one?

Any help/pointers will be greatly appreciated.

Thanks,

Nigel

So the window drops of its own volition when the wipers are on. Is this on intermittent wipe or permanent?
Very deep in what now passes as my memory a little bell faintly rings & it reminds me of a similar instance when I had the tf. IIRC the wiper motor creates electrical hash which sneaks into the Pektron box of magic, creating mysterious goings on.
Either this or your car is haunted.
You might try & slug the wiper motor with a suppressor capacitor, about 0.1uf is as a start, connecting it between ground & feed.
It’s then a wait for the rains to arrive. Shouldn’t be long then.
M

Many thanks for the quick response, we will have a look at this tomorrow. My son isn't 100% sure if the wipers are on or off when this happens. The car has been used very little over the past few years, and when we picked it up the passenger side door speaker was not working. I have MGF Trophy, and have all sorts of bits lying around, a speaker being one. So popped the door card off, and removed the offending speaker to find corrosion on the terminals. So sprayed with electrical contact cleaner, problem solved. So I may disconnect the battery and clean all the connections to the BCU (Pektron Magic Box), and see if that improves matters.

Sounds like a stray current issue, yes clean the bejesus out of the electrical connections and check then recheck all the groundings

Clean the connectors by all means but select with great care what chemicals you choose, if any.
WD40 is the sperm of satan & should only be used to scare neighbourhood cats or as a last resort to dispel water. It isn’t a lubricant & it the nemesis of anything electronic.
Contact cleaners should be used sparingly & preferably by someone who has firsthand experience of the damage excess “squirt” can do.
I will only use Electrolube on cotton buds to clean oxidised contacts & allow the natural wiping of joints to re establish a good contact.
If the contact doesn’t perform as designed it should be replaced; a poor, high resistance joint will create a hot spot as current flows, if it is in amps, or the total attenuation of signal if in milliamps. Signals can track across certain types of “cleaner” & disappear, taking any chance of fault finding success rapidly away. Instances like these will only accelerate disaster.
M

As Airportable said, this looks like wipers motor spike which can be resolved with capacitor suppressor or replacement motor from older version of MG, or completely new motor.

Worth to read here:
https://mgtf-de.translate.goog/tech/wischer/index.html?_x_tr_sch=http&_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en

That’s brilliant David, I wish that service bulletin was available when I had my initial problem.
Guessing at 0.1uf was out by 469.9 uf but it was moving in the right direction.
Anyway, that’s another for the archives.
M

When I posted a link which David screenshotted I did not pay attention of the capacitor value. However, when you mentioned it I remembered that Paul mentioned something about value of the capacitor and its position, so I found it and wrote all here: https://www.the-t-bar.com/forum/roverlike-s-guides/98881-mg-tf-2004-2005-driver-window-opens-or-horn-sounds-all-by-itself#206137

Original MG-Rover proposal was 3.3uF, but Paul suggested 0.22uF as close to wiper motor.