gfci on 2 wire branch circuit

[electricalist]

Plug had 2 wire plug. Changed it to a gfci..line in , load out.
Now when the hall light is turned on it trips the gfci.
With the bulb out it doesn't trip if switch is turned on, its a 3 way wired with 12/2 as travelers.
I'm only guessing, when 12/2 for travelers were used, the hot and neutral could easily be from diff phases. So my gfci keeps tripping.

 

[iwire]

The neutral for the light is from another circuit.

Forget using the load side, just splice the line to the load and pigtail to the GFCI.

 

[electricalist]

That's what I was going to do.
They call me weekly to fix something.
They never complain,and when I spend hours working on something , they always say you can come back tomorrow.

Yes its the in law service call:weeping: