Serious Electrical Question....
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
Serious Electrical Question....
When testing a "hot" wire in my Vette with a multi-meter, I'm getting a 12.4 volts reading, BUT when I check the same wire (and the same ground) with a test light, I'm not getting any light from the test light..WHY???? I checked the test light on the battery (ground to the negative post and the test light on the positive post) and I get a BRIGHT light...so I know the test light is working properly. I also checked the multi-meter on the same battery...works perfectly. What is this telling me????
Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
It's telling you the hot wire is a high resistance circuit. When measured with the high impedance meter which places almost no load on the circuit, you get 12.4V but not with the lamp that draws significant current. You can verify this by connecting the meter and while it is connected, connect the lamp next. The voltage will drop from 12.4V to almost zero. Let me know if this helps. (an understanding of Ohm's law is useful)
Joe
Joe
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
It's telling you the hot wire is a high resistance circuit. When measured with the high impedance meter which places almost no load on the circuit, you get 12.4V but not with the lamp that draws significant current. You can verify this by connecting the meter and while it is connected, connect the lamp next. The voltage will drop from 12.4V to almost zero. Let me know if this helps. (an understanding of Ohm's law is useful)
Joe
Joe
If that's the case, what do I need to do it fix it?
Racer
Joined: Sep 2014
Posts: 429
Likes: 29
From: Brooklyn, MI
When testing a "hot" wire in my Vette with a multi-meter, I'm getting a 12.4 volts reading, BUT when I check the same wire (and the same ground) with a test light, I'm not getting any light from the test light..WHY???? I checked the test light on the battery (ground to the negative post and the test light on the positive post) and I get a BRIGHT light...so I know the test light is working properly. I also checked the multi-meter on the same battery...works perfectly. What is this telling me????
2026 Loser of the Year
Joined: Sep 2013
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From: New Or-leens Loo-z-anna
"Fixing" the wire could fry a component or cause a fire when it is plugged in and left alone.
So.....you/we really need to know what the wire "does".
Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
I've had them installed for about a year and this morning they quit working. Man, I hate electrical problems! The "hot wire" is to the switch in the dash that I installed. It's a toggle switch. Any suggestions on how to fix it? I changed out the relay with a new Hella Relay...still no go. The chances that both lights went out at the same time is highly unlikely...so I don't think it's the bulbs. Could it be a bad ground?
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Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
OK, We need to know how the switch and relay is wired. For example it could be used to ground the relay coil or it could be supplying 12V to the relay coil and the other side of the coil is grounded.
Can you sketch how you think it is wired or a picture of the Hella wiring diagram?
Joe
Can you sketch how you think it is wired or a picture of the Hella wiring diagram?
Joe
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
OK, We need to know how the switch and relay is wired. For example it could be used to ground the relay coil or it could be supplying 12V to the relay coil and the other side of the coil is grounded.
Can you sketch how you think it is wired or a picture of the Hella wiring diagram?
Joe
Can you sketch how you think it is wired or a picture of the Hella wiring diagram?
Joe
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
Sounds like there is a bad connection on that connector shown in the picture for the red wire, perhaps the other two as well. Where is the connector located and is it a location that could be prone to oxidation? What does the yellow wire do? Must be a lighted switch.
Last edited by JimLentz; Mar 27, 2015 at 04:06 PM.
Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
Agree should check connector both sides with test light if not the fuse.
Might also be a corroded connection at the battery if wired like picture.
Joe