Looking for a short can be maddening not doubt.
Id disconnect the battery and start checking each wire with an ohm meter to ground on the lowest scale you have. You should not get even a quiver on the meter is a line is good.
Quickest way to isolate the issue is at the fuse block. Pop each fuse up and check each side. If you get no zero reading (direct short) then you will have to come up a scale or two and repeat the test until you find the circuit that is giving you the problem as shown by getting a reading.
If the issue turns out to be a multiple connection cluster, pull them off and check each one. That procedure will at least get you to the right circuit that is giving you the problem. I would start on the power side of the fuse block rather than the item side.
You may just find its going to be easier to run a second wire to repair the bad one rather than trying to find the physical short and fixing that.
DVM's are super for working on vehicles as they are more than accurate for us, the are quite durable and best of all for a good working tool, they are cheeep. They are readily available on our favorite auction site for under $10 delivered.
I cant seem to post the same pic twice so here is a link showing the meter I am talking about.
A good place to find a 12v Always live source