The following is just my 2 cents, based on work experience-

When I was building an instrument that was to operate in a vacuum of 10^-11 torr (That is about 1 hundred-trillionth of an atmosphere) I looked long and hard at how to insulate the wires... Most common insulators outgass in a vacuum- One common way of doing it was with glass beads around the wires, or beads of Alumina ceramic... of course this was clumsy, and made the system tougher to pump down due to all the small volumes created by the beads.... Then I found out about Kapton coated wires...

Kapton is an excellent insulator that is extremely vacuum compatible... It makes wiring up vacuum compatible systems simple and clean...

At my last job we used Kapton wires - it was exposed to HARD UV, and so I looked up how it handles UV radiation- there were MANY studies on kow it handles space environment- it apparently holds up well....The fact NASA had so many studies on it suggests they use it...

Finally, and this is just my opinion, the wires in the picture taken of the lander by the rover looked like Kapton wrapped wires....

So I think wires themselves are unlikely to short, and I think the microcircuits would be Very well isolated and protected...I would bet on
1) software (yeah engineers always jump on software)
2)Electronics glitch due to energetic particles(I actually doubt this, since we have so much experience with that)
3)Who the hell am I kidding- any cause we propose is nothing more than S.W.A.G.*

All we can do is cross our fingers..

* S.W.A.G.: Some Wild Ass Guess