Fluxgate Compass Extension

[PetrelMarine]

I had a question regarding whether a Raymarine Fluxgate compass cable can be cut/extended. I have been asked to investigate an issue with erratic heading behavior on an autopilot system. The compass cable has been cut to within two feet of the compass and then extended approx 25ft using twisted pair shielded (foil & drain) data cable.

The uninsulated(bare) wire on the compass cable has been connected to the foil/drain wire on the data cable but I noticed the compass cable itself seem to be unshielded I was wondering if interference on the data cable could be causing an issue if the uninsulated bare wire on the compass cable isn't meant to be connected in this manner. Hope this explanation makes sense, is this an acceptable practice?

As always, thanks for your help