I have a 1997 ford expedition eddie bauer. the speedo is not working and it sent it into limp mode. i had it at the shop for about a week. they called and said come get this thing i cant figure it out. this is what my issue is. i started checking everything and found that the wire that is supposed to carry power to the vss is acting as a ground. also 7 of the fuses in the fuse box in the cab are grounded but not blown. i unpluged the pcm and checked them again. still grounded. unpluged the g.e.m. and still grounded. what could cause this?