Shoutout to the old timer who showed me the real way to test a coolant fan switch

I was helping my buddy with his overheating Civic and we were about to order a new fan. This retired mechanic at the parts counter told me to just ground the switch wire to the chassis with a paperclip. The fan kicked right on, so the switch was fine. It was a bad ground connection at the sensor itself, fixed it in ten minutes. How many of you still use that simple trick before throwing parts at a cooling problem?

2 comments

2 Comments

campbell.max17d ago

Saw a video where a guy used a test light to check for power at the switch connector first. That extra step confirms you're getting voltage before you even start grounding things out. It's a solid method to avoid chasing a bad wire from the fuse box.

nora_chen17d ago

That video method skips a key safety check. If the switch connector shows power, you still don't know if the ground path is good. I always test for a complete circuit first. A multimeter checking voltage drop under load tells you more than a test light just seeing if power is present. It adds one more step, but it finds problems a test light will miss.