Understood, and thanks for clarifying. I would leave it at 20A for now, and then when you've freed up all the mechanical stuff, measure the motor current loaded, while it is operating the mechanism. A good general guide is to fit a fuse rated at twice the normal operating current. You might need to experiment, because we don't yet know how big the start-up surge is.

Measuring the motor current unloaded will be meaningless because it will be a small percentage of the loaded current.

I seem to remember when the motor packed up in my daughters car a few years ago it isn't fed directly from the switch but there's an ECU built in. The ECU protects the motor, the fuse only protects the wiring. Once the motor has died the ECU will remember the overload and needs resetting before it will work again. How to do that is the bit I can't remember but hopefully someone else will tell you.

Here's how to reset the ECU
https://the75andztclub.co.uk/forum/s...et+sunroof+ecu

Thanks Steve and Geoaff.

I am getting there slowly.
Some advice from elsewhere is incorrect. Cant remove the motor to reduce the drag as the motor section has the allen key socket to manually operate the sunblind. I have given it several squirts of WD40 over a couple of days to see if it would free it up and this morning gave it a squirt of silicoln lube and have n=managed to move the glass manually enough to expose the front bit of the slide rails. Its absolutely manky!!
Am going to try cleaning and spraying and get it to move its full travel and lubricate it with a smear of grease before trying to refit the motor/controller and try and move it on the switch.
I note what is said about some electronics protecting the motor from overload but there are many reports of burned out motors. Will try and measure the motor load current both out of the controlled and in the car but not sure how to tap into the power (as opposed to the controls) to measure; didnt manage to measure the motor current when the controller was attached to the motor out of the car; will have to try a few different terminals.

Hello Norman,

You can't tap into the motor circuit alone as from the technical information it appears to be an integral assembly with the ECU.

One unintrusive method is to place your ammeter in series with the battery and note the reading. Now operate the sunroof and note the increased reading. The difference between the two will be the sunroof's consumption. The ECU electronics' contribution will be negligible so can be disregarded.

You mentioned reports of burned out motors. I suspect that a more accurate description would be that the electronics failed (did owners really take the assembly to pieces to determine the cause exactly?). I experienced exactly this with my Citroën's sunroof, twice! As a result I resorted to operating it manually using an electric window rocker switch. The motor is fine and simply stalls when friction between the panel and runners becomes too great. It hasn't burnt out.

Simon

There have been a couple of motors that have caught fire in the past.

One was Kermit that I owned, the previous owner had to tear off the cover to get to the motor to stop a fire!

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Hi Simon; thats a good idea!
Only tried that before to find what was draining the battery by pulling fuses.

Have SWMBO cleaning the sunroof tracks with cotton buds; managed to remove lots of muck. Have greased the trancks and had it travel full fore and aft using an electric drill on slow speed; seems to be working. Will re-connect and see what happens. Can re-assemble and try the ammeter on the battery as suggested. Watch this space. (and have my fingers crossed!)

Crikey! To be honest, that does sound like a failure in the ECU. It will be designed to switch off the motor when the current exceeds a certain level, or when the motor has been drawing current for more than a certain number of seconds. Probably much like the electric door windows.

If it controls the motor using a power transistor H-bridge, which seems likely, the most common failure mode for power transistors is, unfortunately, to go short-circuit. Once that happens the ECU loses control of the motor, such that the motor will run continuously (or rather, remain stalled and drawing a heavy current continuously - an excellent recipe for smoke and maybe flames). :eek:

Have tried the sun roof re-set link info and it didnt work. When I took the finger off the button it opened about 1/3 Will try again shortly but at the moment am changing clutch/gearbox on my saloon.

Ref the current measurement my multimeters will only take 10AS; hoping to borrow one from a chum who is an electrical contractor.

Have got the sun roof to free up by manually opening and closing it and cleaning/lubricating the slideways. Ran it with an electric drill on the manual open/close that exposed a bit more dirt thats been cleaned and lubricated.
As per sugestion have tried to measure the current drawn as it has a 20 A fuse that seems a bit big. Used a clamp type ameter on the +ve from the battery; it showed some .01 A when the ignition was turned on (its a diesel) and then4 or 5 A when the screen motor was working opening/closing the roof. What I am not sure about is whether the reasdings are correct? Does a clamp type ameter work properly on DC current or only AC current???? Answers on a postcard please!:shrug: