I would suspect that it is picking up the ground from the shield of the video cable. It would still be best to connect a fixed power ground at the camera too.
+1 This.
I would also expect for it to fail prematurely if not properly grounded.
on a similar side note, had some dude come in to the shop the other day. he is a self proclaimed "wire guy". he says that he has "fixed up" in tons of radios. he has a chysler cirrus, mid 90's and he fixed up his own radio, the problem he is having is that the radio works fine when the volume is below 5 (it goes up to 35) but when turned up to 5 or above, it instantly shuts off and then turns back on and will repeat this loop until turned down below 5.
he then proceeds to tell me that the reason its doing this is because he has fixed up some legacy 500 watt speakers all the way around and dat dem be so thuursty, dat dey sucking the radio dry... and then wanted to know if i had a 2000 watt 4ch that could feed them properly #RollsEyes
well i've got all the info i need at this point, and tell him that i will trouble shoot it an mostly likely can fix the problem in 15 min for $20 (standard shop rate is $80/hr), we usually have a 30 min minimum but i know what was wrong and it was a pretty easy fix and i had already wasted over 20 min listening to him try to tell me what is wrong...
guy hears this and just flips out, telling me that i should just fix it for him cause he has already done the install work for me.
after another 10 mins of this he tells me to go ahead. pop the radio out and exactly as i thought, the only ground the radio had was through the shielding of the antenna wire! since all chrysler vehicles before 2000-2002 dont have a ground in the harness, they usually have a ground strap or wire clipped on separately. (the crazy part is that on that entire generation of cirrus/stratus that is actually how the factory did that) works find for the small amp in the oem radio, but as soon as the current draw picks up, the shield cant keep up.
best $20 of my week!