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?

3 comments

3 Comments

campbell.max1mo 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_chen1mo 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.

kelly.parker21d ago

Man I still do that paperclip trick and half the time I end up shocking myself because I forgot the key was on. My buddy called me MacGyver once and I burned my thumb so bad I couldn't work on cars for a week. Now I keep a cheap test light in my glovebox specifically so I don't have to be a hero with a paperclip anymore. But yeah that old timer's method saved me from replacing a perfectly good fan on my old Pathfinder last summer.