I seem to have an electrical gremlin:

When I apply the brakes, I get an alarm that says the rear gate is open. (And interior lights come on). Same happens when I activate the rear wiper. 
 

Also, I cannot open the rear gate. Button & fob does nothing.

 

it started doing this occasionally a couple of months ago. Now it’s all the time.

 

Anyone have any ideas?

 

My suspicions are:

1) water in electrics (In the past, it seemed to be correlated to wet weather)

2) damaged insulation 

 

Not sure where to begin...

 

It’s a 2014 SMAX

Check the rubber conduit where the tailgate wires run through to the roof.
The wires can snap due to the insulation getting brittle over time and condensation then causes a short circuit.
I had this on a MK1 Focus whereby every time I pressed my brakes the power crossed over to the boot lock solenoid and popped the boot open.
Rear wiper also packed up, allowing ony the intermittent wipe to function.
Cure was a bit of wire cutting & splicing to bypass the corroded and frayed wiring, a new boot lock mechanism plus a new wiper motor.
The near constant flow of power had burnt out the solenoids / motors in both.

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Thanks. Trouble is I can’t get the boot open. 

does sound like  the wiring in the left  rubber grommet. if the tailgate wont open, you need to manually open it. i did post how to on the s max section. willsee if i can find it. 

edit, cant find it but found the ilustration

basically from the inside , you need to cut a section of plasitic way (1) then push the lever with screwdriver(2) 

Thanks!

 

It has magically started working again. But of course, cannot do much about it now. 
 

How does one inspect the wiring going into the roof? I had a fiddle there and it wasn’t immediately obvious how to pop it open

 

Thanks again 

There is a plastic insert inside the rubber tube where it enters the tailgate. There is a knack to removing them complete with a screwdriver. But I find it easier if you forcebly peel the rubber out from the insert around the tailgate, then you can see the plastic insert to then get a screwdriver in and bend the locating tabs on the insert. Once that's out you can push it out the way to see the wires.