Abs light

Okey maybe someone will be able to help. I got 2014 780 and my trailer abs light keeps turning on for about 3 seconds every time i press on the break both dash and trailer. If my truck is off no ignition and i press on breaks trailer abs light illuminates for 3 secs. Original i thought there is a problem with trailers bendix system so before trying to fix things i hooked up to my buddy's new box and what do you know the light was also triggered same as it does on mine. We figured it could be a power supply connector or a cable so I've changed both...well now that POS not is only triggering abs light when breaking but i s*** you not it turns on when i put my right but only right turn signal on lol. When i turn the key for ignition to test the light it illuminates on dash for 3 sec but its not turning on on the trailer. I checked the fuse under hood and its not blown. I really have no idea wtf is wrong anymore. Miraculously i passed level 1 in CA with that but i feel like one day i won't be so lucky

Btw if anyone is planning to buy volvo do yourself a favor don't!! I've owned this pos for about 2.5 months and already spent $20k in repairs truck is not even pushing 400k miles on clock.

 

Ive tried doing that blink code diagnostic few times already but nothing happens. Do you think that even though this is obviously a problem with the truck not the trailer there would be fault codes showing through trailers bendix?

 

Maybe im doing something wrong but to my understanding blink code diagnostic goes like this: turn the key to ignition wait about 15-20 seconds for the system to cycle than apply the break for 1 sec and release, repeating it 3 or 4 times. Trailer is 2009 utility i already posted that question in another thread with trailer abs problems as i thought that's what it was. Now im pretty sure the truck is causing this bs

 

As i stated before ive checked the fuse under hood and its fine unless there's another somewhere else. What's really funny is why would trailers abs light be triggered by turning on right turn signal and like i said that only started going on after i switched to new power supply cables

 

Okey will do thanks. I have to stop somewhere and get a test light as i left one at home. Will that be fine or should i get more accurate voltage meter?