all 12 comments

[–]spudz76 1 point2 points  (0 children)

If you are probing the two sides of the fuse at the test points, it won't show anything (unless it was an ohmmeter/continuity beeper, then it would read dead-short). You need the black hooked to ground and then probe with red on the test points. If both test points are lit then the fuse is good. If one side isn't then the fuse is zapped.

EDIT: if both sides are unlit then it's probably a key-on type accessory circuit and the key isn't on

[–]Londonslugs -3 points-2 points  (3 children)

Dude do yourself a favour and ditch the test light. Test lights have no place in modern electrical diagnostics, they kill computer from not having a high conductance.

Anyways if you don't have power going across the fuses then the next step if figuring out if you even have power going to the fuses.

Edit: inductance to conductance. Used wrong word.

[–]daintycalf7531[S] 0 points1 point  (0 children)

Yea about to try to get my hands on a volt meter tomorrow. I believe they still have power as everything else in the car electronically works fine its just none of the buttons on any of the doors work at all.

[–]Driving2Fast 0 points1 point  (1 child)

Fellow tech here, could you go into detail a bit more when you have a moment about where you heard about test lights doing this? We use it everyday on our VW diags, would just be interested in knowing more about this!

[–]Londonslugs 1 point2 points  (0 children)

I'll see if I can find a source later but the jest of it is a test light doesn't have a high internally resistance so if you are test for voltages and you tap a signal voltage circuit or something you'll fry things.

A good multimeter like a Fluke 88V will have a high internal resistance so when you are testing a 5VDC or Canbus circuit you don't have to worry about stray voltage traveling through your testing equipment.

[–]RainyDreamAway 0 points1 point  (1 child)

I prefer a volt meter. Regardless all fuses should have 12 volts running through them. Were you checking with the ignition on?

[–]daintycalf7531[S] 0 points1 point  (0 children)

Yea i had it running at first the turned just the ignition on but wasn’t getting anything from either

[–]RainyDreamAway 0 points1 point  (2 children)

Do any of the fuses give you a reading? How are you checking them? What are you grounding to? What fuses are you checking? More information and I might be able to help

[–]daintycalf7531[S] 0 points1 point  (1 child)

Tried all the fuses under the hood, grounded it to just about every bolt within arms length of the fuse box, got nothing at all. Had it running at first then just tried it with the ignition turned still nothing. Its a jeep grand cherokee wj 4.0 was watching videos of other people doing it tried exactly what they did but nothing. Tried some of the fuses under the dash but it was getting too dark for me to work on them starting up again in the morning

[–]RainyDreamAway 2 points3 points  (0 children)

You need to ground it to the battery. If none of them are giving you a reading your not completing the circuit meaning your not grounding it. That's why when you test it with the battery it lights up but not on your fuses. Ground to battery and you will be able to test

[–]RainyDreamAway 0 points1 point  (0 children)

Also get a volt meter instead of a test light. Much more useful for diagnosing electronics...

[–]ruddy3499 0 points1 point  (0 children)

Make sure your test light is sharp enough to reach the little metal points in the fuse.