Toyota Repair: how to find a short, amp fuse, continuity tester

Question
Captn. Ritter! 84 Tercel(4wd 3A-C) has a bad ground in the tail/dashlight circuit.
The 15 amp fuse blows when I turn the parking lights,and/or headlights on. I
have been doing circles around this circuit with a continuity tester and ohmeter
for three days, CAN'T FIND SHORT OR BAD GROUND IN ANY BULB OR SWITCH!
only have one fuse left, losing mind, please help. ACLUELESS PREVIOUS OWNER
HOOKED UP TRAILER LIGHTS BADLY-could this cause an invisible short?

Answer
Hi, there is not invisible short. It is there I am sorry that I can not help you much, but if you have constant short, it is actually easier. you will need wiring diagram to trace it. tell me witch circuit U have problem with.

remove bulbs and look inside socket. Sometimes people will install bulb with one connector at bottom in place where two are needed and will short the circuit.