Ground Question

I hope I'm posting this question in the right place, my apologies if this is the wrong forum.

On my 1972 Plymouth 340 Duster the power steering went out on me. I take it to a shop and had the mechanic there fix it. When I got it out it ran good but a few days later when I drove it at night I had no lights on the instrument panel. The radio lit up fine, I had all my exterior lights even the dome light works. Only the instrument panel wasn't working.

So by process of elimination and figuring that my mechanics had left something loose because everything worked prior to them getting their hands on it, I looked around the steering wheel area and discovered one of the bolts underneath that appeared to anchor it had frayed wires coming from it. Assuming what seems obvious is that there is a wire that comes from the instrument and grounds it to that very bolt. My question is which wire is it?

I figure I should fix it myself since it seems like everytime I put this car in the shop I have to take it back 3 more times after that to get something else fixed that wasn't broken before I took it. Powersteering led to a new gas tank that leaked which meant I had to take it back 3 more times and the leak is still not fixed. Keep in mind that when I say new I mean brand new. Did I mention how I all of a sudden needed a NEW radiator when the old one suddenly sprang a leak mere hours after I pulled it out of the shop?

I'll try and take a photo and post it.