Hi all, bit of a strange one I've not seen before so I've come to consult the experts.

 MK2 07 plate Zetec. 

Sporadically the passenger side indicator will start flashing rapidly as if a bulb has gone, but all indicator bulbs are fine. At same time the dipped beam on same side dims to about 25% output. This lasts for a while and then just goes back to normal, dipped beam back to full power, indicator working normally. 

Thinking a wiring/earthing issue but to be honest I don't have a clue. Anyone got any ideas? 

I'd go with earthing or water ingress somewhere

I’d have a look at the bcm/gem under the glovebox.  Lots of plugs on it.  Try unplugging and reseating the plugs and see if any corrosion.  Inside the bcm are circuit boards with computer chips on.  Sometimes water gets inside there. 

Very probably the GEM (BCM). As Isetta has said check for signs of water ingress.

On 2/5/2022 at 11:51 AM, Denimchicken said:

Hi all, bit of a strange one I've not seen before so I've come to consult the experts.

 MK2 07 plate Zetec. 

Sporadically the passenger side indicator will start flashing rapidly as if a bulb has gone, but all indicator bulbs are fine. At same time the dipped beam on same side dims to about 25% output. This lasts for a while and then just goes back to normal, dipped beam back to full power, indicator working normally. 

Thinking a wiring/earthing issue but to be honest I don't have a clue. Anyone got any ideas? 

You have a bad earth, follow the wiring harness back from the headlamp, somewhere between the headlamp and the suspension strut on the inner wing you should see 2 black wires exiting the harness and fixed to the body. Usual for the fixing screw to corrode and break off when trying to unscrew so be prepared to make a new fixing!
This earth point is for cooling fan, horn & fog lamps as well.

3 hours ago, Dan62 said:

You have a bad earth,

Having re-read the fault I think @Dan62 is probably correct.