Fiesta ST indicator problem

Get someone to help you test it. Have them hold the brake pedal/select reverse/switch lights & fog-lights etc while you watch the light cluster when the indicator is switched on that side & make sure everything else is working properly. If you notice another light working oddly, like the brake light blinking in that cluster when the brake & indicator are both active, it might indicate something like your indicator on that side not earthing properly. If you get an odd result like this & are able to identify the wiring properly, you can test the indicator working properly by switching it on & earthing the circuit from the loom to bare metal, if doing this resolves the problem it can be fixed easily by running a new earth to the body.

With the bulb removed have a look inside the bulb holder, check that the holder itself is clean & dry with no signs of moisture or corrosion. I’m not familiar with the Fords particularly but there’s normally metal contacts of some form in the bulb holder, make sure they’re dry, clean & able to make good contact with where they should be on the bulb. The contacts can often get dirty or look like they’re black at the end where they contact the bulb, they can be easily cleaned with a small file/sandpaper or even scraped where they’ve blackened with a small flathead screwdriver. They don’t have to be winning any cleanliness awards just make sure you’re getting a metal-to-metal contact when the bulb is back in the holder.

Check the wiring loom from the light cluster as far as you can back towards the inside of the car. Double check if the loom goes through the car body (normally inside a rubber sleeve) when the boot is opened, sometimes wires within the looms can get caught/cut or ground mistakingly at movement points such as these.

While you’re working around the boot area it might be worth removing all the boot-floor coverings to check for any moisture underneath. In our lovely climate our cars can often hold any water that gets in & with so many cars now storing electronic control boxes/batteries etc in the boot these days it’s worth having a peek, especially in a car that’s not driven much. I was off the road recently for 12 months & the (relatively modern) car had attempted to transform into a swimming venue while parked up.

If you get this far & have no luck fixing the issue you’ll probably have to take it to a professional. Hope you get it sorted but please, if you’re unfamiliar with these in-car wiring systems it’s often not worth poking around. If in doubt, go to the experts!