Motorcycle Repair: 85 VT500, vt500, loose connection

Question
How do I check to see if an electronic tack is working , the bike I purchased had on tack so I picked up a used one , i installed it and nothing , I checked the fuses and replaced it ,  I am guessing that the previous owner took the tack off thinking it was faulty , any tips on what I should look for ?  I would like to restore the bike back as much as possible . with out the tack on wires are hanging out

Answer
Paul, the tach gets it signal from the spark boxes under the seat.  You need to check the wires from the spark boxes to the tach to make sure they are connected.  There could be a loose connection or a broken wire somewhere.  If the bike runs, the spark boxes are okay so it has to be in the wiring somewhere.  The tach also needs power from the battery so make sure the brown and white wire has 12 volts on it.

Regards
Rich