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MM vs Test Light


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uglyb0b 
Copper - Posts: 55
Copper spacespace
Joined: January 18, 2005
Posted: February 08, 2005 at 7:29 PM / IP Logged  
Hello all. I was wondering if someone could take a few moments and educate me on how (technically) a multi meter is safer than a test light. A long time ago, I installed new stereos in cars. This was way before air bags, computers, etc. I simply used a test light and everything was peachy.
I understand now that using a test light can damage a circuit/blow an airbag/etc, whereas a mutli meter cannot. I am wanting to know why.
I’m not looking for an argument that you need to use a mm over a test light. I get that. I would just like to understand why for me.
For example: is a test light more of an “intrusive” or “active” way of testing, and can complete a circuit (hence blow an airbag)? Whereas a mm is more of a “passive” testing method? In other words, a mm just sits there and tells you whats going on (voltage wise) but doesn’t actually intrude on the circuit like a test light can/will?
Any clarification someone can provide would be appreciated. Thanks.
benjammin74 
Member - Posts: 24
Member spacespace
Joined: July 10, 2004
Location: United States
Posted: February 08, 2005 at 11:28 PM / IP Logged  
you answered your own question. test lights are obsolete. no clarification needed, just be safe and don't use one. its not worth the risk.
car audio pays my bills...
kgerry 
Platinum - Posts: 3,455
Platinum spaceThis member consistently provides reliable informationspace
Joined: February 07, 2004
Location: Saskatchewan, Canada
Posted: February 09, 2005 at 9:20 AM / IP Logged  

the circuitry of a MM acts as a filter, which prevents blowing things up....

the problem with test lights, even the "computer safe" test lights, is that they illuminate with anywhere from 2 volts to 18 volts..... i've been burned in the past from assuming i had a good connection/circuit because a test light lit up, only to go back to that same circuit after 20 minutes of further troubleshooting and meter it properly with a meter and find out i only have 4 or 6 volts, where i should have had 12 or 14 volts....... this whole industry is about remembering the lessons we learn along the way.... for the past 10-15 years all i use for circuit testing is a good quality digital MM ( analogue when checking for shorted speaker wires )

Kevin Gerry
Certified Electronics Technician
MECP First Class Installer
Owner/Installer
Classic Car Audio
since 1979
traitorhound 
Member - Posts: 13
Member spacespace
Joined: January 25, 2005
Posted: February 09, 2005 at 9:42 AM / IP Logged  
kgerry, why analog mm for speaker wires?  just curious
riceman 
Copper - Posts: 109
Copper spacespace
Joined: October 14, 2004
Posted: February 09, 2005 at 2:09 PM / IP Logged  

Kgerry ,what about the powerlogic II probe, is that a safe probe to use ? I've accidentallly used it when trouble shooting an RS and probe the tach wire by accident and nothing happened. I would never use a powerlogic to find a tach wire. I would use a DMM to find  tach . I've used that snap-on  hummingbird, mac , those all leak ground. I've found the that the powerlogic II probe makes my job alot easier. But I'm still very cautious when using it, when in doubt I still rely on my DMM. I think that with common sense you can use test light & logic probe. But I was wondering what are your opinions on the powerlogic II probe? thanks

kgerry 
Platinum - Posts: 3,455
Platinum spaceThis member consistently provides reliable informationspace
Joined: February 07, 2004
Location: Saskatchewan, Canada
Posted: February 09, 2005 at 2:19 PM / IP Logged  

no real reason per se, just habit... when you see the needle start to climb you know you have continuity to ground ( where you shouldnt )... i bought a couple of good analogue meters when i opened in the late seventies, early eighties and they still work fine so thats what i use.... it's actually quicker for testing than waiting for a DMM to auto-range.... 

Kevin Gerry
Certified Electronics Technician
MECP First Class Installer
Owner/Installer
Classic Car Audio
since 1979
kgerry 
Platinum - Posts: 3,455
Platinum spaceThis member consistently provides reliable informationspace
Joined: February 07, 2004
Location: Saskatchewan, Canada
Posted: February 09, 2005 at 2:24 PM / IP Logged  
i use logic probes for checking data, but never used one to check tach... any DMM with an AC setting will test tach fine....
Kevin Gerry
Certified Electronics Technician
MECP First Class Installer
Owner/Installer
Classic Car Audio
since 1979

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