Alarm and heated rear windows related ?
 

I have this on going problem with my car alarm for quite a while where is set off randomly and mostly at night. For over a year Im locking my car with the key just not to arm the alarm.

At first I thought is siren module as many people suggest but I replaced module with new one from dealer for £200 w/o luck.

I also checked wires that runs on left hinge on tailgate door and they are in good condition without visible cuts

Few times ( x5 in last year)message appears on dash saying that my tailgate is open while driving ( ones or twice after I run thru small pothole).
I checked for some loose connectors but I couldn't find any

replaced a tailgate latch with used one from forum member cos I though it may be micro switch but that didn't help alarm still goes off randomly.

Yesterday I have suggestion from mechanic that the conductor tracks of the rear window heater printed on the rear window are damaged and they can cause alarm goes off and tailgate open message appears on dash.|

He suggested that is possible to make this alarm problem goes away but I will lose defroster .I would prefer to keep both but I'm happy to lose alarm if that is the option

Not sure how easy is to fix them as my rear window is tinted and removing tint can do more damage.
Replacing whole glass is the option or removing alarm with software from dealer is the other one and probably cheaper option.

I do work on my car etc but electric is like black magic for me. I have multi meter at home but I'm not very good with using one

Car is V70 2.4 n/a 2006

https://i.imgur.com/BgJzbCj.jpg
https://i.imgur.com/ul8Sefj.jpg
https://i.imgur.com/4ydwEXC.jpg

Yes they are related. A signal wire, Pink, comes from the CEM through the lock microswitch on through the demister and on to earth. If it gets broken, or the window gets broken you will get alarm messages and the remote flashes on lock unlock are different or absent on either lock or unlock.
The wires at the hinge can break inside with no external signs of damage.
I would check for continuity from the black earth wire at the demister and a good body earth and open the plug to the tailgate wires up inside the upper access panel to the right tail cluster and check for continuity in the pink wire with the latch closed over. Wiggle the harness at the hinge.

Thank You Brendan.

I checked all wires for continuity incl pink ,black and also brown which is connected to demister with latch open and closed over and it looks all good.
I dont know what else I can check. I'm booked at volvo dealer next week so I will probably ask them to disable alarm cos I'm bit tired of all this.

Im not sure how long it takes to arm the alarm system but sometimes it takes few hours for alarm to go off.

When you checked the wires that run through the tailgate are you sure you pulled them out far enough to validate that they are fine? I did same for a friend of mine and recall pulling them out a couple of inches and saying, all good here. I then decided to pull out some more and WOW, most wires were all but severed. To pull wires out more, you need to take inside panel out and unclip the wires from one of those plastic harness clips that fastens to frame IIRC.

Just to add to Pierre's comment, I found it easier to inspect and work only after disconnecting the plug inside by that harness support.

This sounds like my issue from some time back
https://www.volvoforums.org.uk/showthread.php?t=192701

Additionally i'd check continuity from one side of the rear screen to the other. If it was not working I'd suggest you would have noticed the gaps " undemisted"

Cheers
Bob

Thanks Pierre. I removed all plastic panels/covers from inside and from tailgate and I properly checked the wires and they all looks good.

If you meant tie zip plug Brendan ...the one above speaker which holds wires then yes. I actually removed that permanently one cos I thought it may cause the problem when you closing tailgate.

Thanks Bob. Do You mean continuity from red to black wire? There is also continuity between window brown wire tag on the left and the one which goes to micro switch so I suspect the problem is where the brown tag is attached to the rear window or am I wrong
Demister its working fine except top printed line which is broken for unknown reason

As only one line of your heated rear screen don't work don't think this is the issue...Id re earth / additionally earth the brown wire to the black light wire as I did to guarantee a good earth. Sounds to me if you have an intermittent fault with the std brown earth point by the side glass
Cheers
Bob