The biggest problem here is that if it is electrical....it will be hard to find as it appears to be intermittent.
So doing static measurements are not likely to find the problem if there is a wiring issue that only shows up when hitting a bump in the road!
I was fortunate with my problems in that although they started out as intermittent they became solid so that I could make all my measurements in the garage!
Electrical problems are a pain but years of fixing them put food on my table and a roof over my head and helps me fix issues that the local Dealers merely scratch their heads at