Did you know this about Fuses and testing in circuit?
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Did you know this about Fuses and testing in circuit?
Guys, I love it when something so simple humbles me. I've been working on electronics most of my life, never thought I knew it all but wow this one is about as simple as they get and I just realized/learned it today I wanted to share (if there's anyone who never realized this too).
Today I strarted to trouble shoot why my front fog lights don't come on. It's fuse 17 in the engine compartment BTW. Checked the fuse, she's good. Now I wanted to check for 12 volts under different conditions. Darn, the access to the contacts in the fuse block are restricted so I thought to myself "I'll have to fashion something to get my probe in there." Then I looked at the 15 amp fuse I just pulled out - and it hit me: On top of each fuse, the side that reads current capacity and faces you when you look at the fuse box there is a tiny rectangular cut out exposing access to the left and right blades of the fuse.
Sure enough it is unrestricted. You can easily just touch your multi-meter probe to the metal connected to each "leg" of the fuse, whether it is plugged in or not. IOW, you can test for continuity (is it open or not) with the fuse plugged in. Furthermore you can read voltage with the things plugged in (one probe on your meter touches ground, other touches one of these 2 points). I've been looking at these things for years (actually decades) and never even realized it.
Hey this is so darn obvious that I may be the only one who never realized it, but just in case it slipped by you - here you go. Hope it helps.
FWIW, I've just proved that the fog lamp fuse gets no significant voltage if the running lamps are not working. Hope its just a simple blown fuse for them, my next step.
John
Today I strarted to trouble shoot why my front fog lights don't come on. It's fuse 17 in the engine compartment BTW. Checked the fuse, she's good. Now I wanted to check for 12 volts under different conditions. Darn, the access to the contacts in the fuse block are restricted so I thought to myself "I'll have to fashion something to get my probe in there." Then I looked at the 15 amp fuse I just pulled out - and it hit me: On top of each fuse, the side that reads current capacity and faces you when you look at the fuse box there is a tiny rectangular cut out exposing access to the left and right blades of the fuse.
Sure enough it is unrestricted. You can easily just touch your multi-meter probe to the metal connected to each "leg" of the fuse, whether it is plugged in or not. IOW, you can test for continuity (is it open or not) with the fuse plugged in. Furthermore you can read voltage with the things plugged in (one probe on your meter touches ground, other touches one of these 2 points). I've been looking at these things for years (actually decades) and never even realized it.
Hey this is so darn obvious that I may be the only one who never realized it, but just in case it slipped by you - here you go. Hope it helps.
FWIW, I've just proved that the fog lamp fuse gets no significant voltage if the running lamps are not working. Hope its just a simple blown fuse for them, my next step.
John
Lol john john john. Did you also know that you can test certain fuses and they test good but can be back fed circuits showing power on both sides too even when bad. Soemtimes best to pull out fuse and look 
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Joined: Apr 2018
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From: Hampton Roads, eastern Virginia
Though to be sure, some fuses are sealed so these access holes don't give contact. Others have access holes so tiny none of my meter probes can actually contact the conductors.
It's something worth considering when buying new fuses. Buy the ones with open holes and you might save some frustration down the road.
It's something worth considering when buying new fuses. Buy the ones with open holes and you might save some frustration down the road.
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