ok, so I bought a used boat and I want to replace all of the gauges to upgrade the look and because more than half of them do not work. Well upon inspection, the ones that arent lighting up, they all have a faulty ground. If I test with multimeter and use the ground of a good gauge and test the 12v connection on the faulty one, it shows power. If I test that same faulty gauge and use its ground and power, it shows nothing...so the ground is bad. The problem is all the wires are in their factory sleeves and harnesses...it would be a pain opening up all that.

Would it be ok, if i just daisy chained off the ground wires that come through to another gauge that is a good one?

That will work fine.. Ground is ground, as long as you have clean secure connections.. On the other hand, cable harnesses are not a big deal to get into, tie-wraps and wire loom are pretty cheap.

Wiring, itself, seldom is the issue. Look at points of connection on the wiring. Most boats have a fuse block/distribution block. It routes 12v+ through fuses and 12v- through 1/4" male spade terminals. Remove the female ground terminals from the male spades and clean each connection. Also check each male spade terminal for a clean, corrosion free attachment to the distribution block. The usually are attached with rivots. Sometimes they use screws and nuts.

Your problem is likely at this fused/distribution area.