Could Testing Trailer Wiring Pins with Circuit Tester Cause Fuse to Blow

Published 10/27/2021

Question:

I installed a 4 pin wiring harness using in a Rav4. Didnt have a trailer yet, so tested it with a multimeter on continuity mode by touching the probes to alternate pairs of pins. Two pins led to a steady beep on pace with turn signal when turn signal was on. Two pins gave a steady beep with the head lights on. Together, suggested things were working. A short time later, plug in actual trailer and nothing. Plug same trailer into buddies truck and lights work. Check my setup and the fuse is blown: Question: Could toggling the multimeter among the plug pins have shorted the fuse?

asked by: Joel

Helpful Expert Reply:

The only way the multimeter could have possibly blown the fuse is if one of the probes ended up touching the ground pin and one of the active pins at same time as that would create a short. Otherwise the short is on the trailer wiring which is probably the more likely situation as this is a common problem that takes out the converter boxes.

So I'd recommend going over the trailer wiring looking for any cut or exposed wire and fixing as needed.

expert reply by: Jameson C