Hi,

So I’ve got a bit of a weird one and hoping to get some help on this please, but my passenger side lighting completely goes out when it rains. Everything else works on the passenger side but the side light and tail light. (Dipped, High, Brake, indicator, reverse all work).

I think it’s something to do with F22 (engine compartment), however I have checked the fuse and it’s fine. The lights work when it’s a dry day just when it rains the issue occurs.

When it has rained or raining.. and I unplug the fuse then all lights come on for around 5 minutes with key turned to electrics, but when I then turn the car on the passenger side lighting goes off completely with all other functions working etc. However the issue fixes itself by the next morning if there has been no rain..

Hopefully this is an easy fix 

Any ideas on what the issue could be? 

Is any rain getting inside the cabin?  Particularly around the fusebox?

Not that I can see, however the boot does leak but no idea where the water is coming from 

Just now, BabyRoo said:

Not that I can see, however the boot does leak but no idea where the water is coming from 

The water may be coming in through the tail light cluster and causing the fault.  Worth checking that if not done already.

I have checked this by using a hose on the rear end but me pouring water all over the car doesn’t have the same outcome as if it rains. But it’s such a weird issue so hopefully posting here someone may have come across this too? 

5 hours ago, BabyRoo said:

passenger side lighting completely goes out when it rains

The sidelights (aka. parking lights) are controlled by the GEM/BCM unit which is part of the passenger compartment fusebox. Often rainwater will find its way in and drip in to the GEM/BCM which can cause all sorts of faults.

The other possibility is that you are getting a short-circuit to ground when its raining and that water is entering either the front or rear light fittings/connectors.

You mention that there is water getting in the boot, so I'd start checking the lamp holder and any electrical connectors in the boot. If the GEM detects an over current situation due to water ingress it will turn off the supply

PS.

your profile says 2008, do you need to update that ?

If you have water in the boot area try looking at the rear of the roof rails..under the plastic

That seam always leaks

Gently lift the plastic rail cover at the rear..

Clear the seam of its old sealant..it will run down to the boot rubber.

I used a black mastic that stays rubber afet setting but also used it to rescue the plastic rail trim

I only used black as I have a dark car

Leave to dry for 24 hours and do a water test

On 7/27/2024 at 5:19 PM, unofix said:

The sidelights (aka. parking lights) are controlled by the GEM/BCM unit which is part of the passenger compartment fusebox. Often rainwater will find its way in and drip in to the GEM/BCM which can cause all sorts of faults.

The other possibility is that you are getting a short-circuit to ground when its raining and that water is entering either the front or rear light fittings/connectors.

You mention that there is water getting in the boot, so I'd start checking the lamp holder and any electrical connectors in the boot. If the GEM detects an over current situation due to water ingress it will turn off the supply

PS.

your profile says 2008, do you need to update that ?

Thank you very much for the info! When it rains next I will check the glove box area for water ingress. I have checked the connections when it’s been raining previously but there is no evidence that water was getting to the connectors but I will give this another look. 
 

Thanks I will update the forum once I had a better look! 
 

I have a 2008 fiesta and my partner has a 2010 

On 7/27/2024 at 9:30 PM, Danny cj said:

If you have water in the boot area try looking at the rear of the roof rails..under the plastic

That seam always leaks

Gently lift the plastic rail cover at the rear..

Clear the seam of its old sealant..it will run down to the boot rubber.

I used a black mastic that stays rubber afet setting but also used it to rescue the plastic rail trim

I only used black as I have a dark car

Leave to dry for 24 hours and do a water test

Thank you, I will check the roof rails with a hose and then can check to see if water is coming through the seams