Welll assume your tailight is O.K. becaus the extra wires lit them. Is this correct?
By the way: One does not use a "sweep-meter" to measure Volts DC. You can use a Multi-Meter or Volt-Ohm Meter. Saw one for $7.00 in Menards a few weeks ago. I am assuming this is what you mean.
With the engine running, what voltage do you have at the battery terminals or Jumper wire terminals?
You may want to take out each of the fuses and check for continuity (zero Ohms) across each fuse. (Same meter, different setting) If you get infinity (a lot of Ohms) you have a bad fuse. Visual checks can sometimes be worthless.
If you put in new wires to the taillight from the battery, did you add a fuse at the battery? If not, you could burn the thing down.
Also, if you have a bypass on the Starter Solinoild flopping' around in there, could that possibly short out and again burn the thing to the ground.
If you have > 12.8 VDC at the battery, when the sled is running, then the sled is charging. Then, remove the fuse in the affected circuit and look for voltage on the circuit on one side of the fuse block. If you have power there and the fuse to be reinstalled is good, then your problem is down-stream of the fuse.
You said things looked O.K. at the tail light. Did that mean that it looked good or did that mean that you checked for voltage and found voltage. You probably did not find voltage, which casued you to add new wires. Is this correct?
Could it be possible that the origonal wires to the tail light got pinched between the seat and tunnel and shorted or mice chewed on them? If YES, that still brings you back to the fuse, if you have power to the imput of the fuse.
When you checked the fuses, did you have to replace any?