When checking fuses ...

When checking for blown fuses under the dash panels, side panels, and under hood.... Is using a test light safe not to cause damage to the cars sensitive equipment such as BCM .. or other .... about how many amps does a test light uses if anyone might know.

what does BCM stands for by the way ?

Think if it like this would you add a resistor to a wire you had no idea what it does ,or maybe what if if it was on an ecu(car computer)?? Probably not, i know i would not, well a test light adds a lot of resistance to a circuit compared to a dmm wich is a verry small resistance,now ifyou were testing a sensitive piece of equipment that cannot take the added draw then you will hurt something with a test light, so being that a meter adds a lot less resitance  there is less chance if any to harm anything. Bottom line use a dmm because test lights are no good in newer computerized vehicles and you cant do anything more than test voltage with a test light you can do a lot with a dmm.

Thanks guys, that makes sense.

Depends on the test light. The Snap-on test light I use only draws 40ma from a +12 volt source which is the same as 3 leds drawing current or from a 5 volt source would draw about 17ma which is the same as 1 led current draw.

Now i have a friend who HAD a test light from a auto parts store and i showed him the difference from a Snap-on one from his. He argued with me saying test lights are all the same until i showed him how much more his test light would draw current compared to the Snap-on one. Well his test light had drawn way over 1amp. Now he uses a LED test light and also bought a Snap-on comparable one.

OK, so if you were working on a ford vehicle, lets say a 94ish Explorer. There are about 5 different yellow wires for 12v in the ingnition column. How would you test with a test light to find which one was correct. All of the wires with test voltage but sometimes only 2 of them will read a true 12v. This is why it is very important to use a DMM. "We always say look twice, drill once" we should take the same care with wires and circuits. It's worth it to do it right the first time.

Brent, Car Audio Manager, Generation Sound

I think kparkk was asking about testing for fuses and not testing wires in ignition column with a test light.

 go2pac,

but aren't some of the wires in ignition column connected to some of these fuses?  If not ... then do you mean thats its ok to use a test light?

After reading what other replied .. it made sense.. now I am confused again.

Thanks for your clarification in advance.

go2pac,

but isn't some of the wires under the ignition column connected to fuses that I might be testing?  If not, then u think its ok to use a test light on fuses?

I understood what other guys have replied .. but you got me confused again

thanks in advance for your clarification.