Electrical stuff
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Racer
Joined: Nov 2004
Posts: 319
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From: Sunnyvale CA
Electrical stuff
Ok so I am going to check out my electrical system tomorrow by pulling fuses to look for "leaks" and I've hear all around the forum that the thing to use is this little light or something that glows when a load is being put on the battery. First off, do you have to use one of these, or can I use a multimeter instead? If I do have to use one of these, what exactly does it look like? Thirdly, I just installed a new sony stereo (DIN style, used with custom bezel). Could I be experiencing a power drain there? Should I install a kill switch for it?
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
You can use an ammeter, but you risk killing the meter if you hook it up wrong or exceed the limits of the meter. Use a 12 volt test light in series with the load. Pull off either battery terminal. Hook 1 end to the terminal, the other to the connector. Any time there is a draw, the light will be on. Pull fuses till the light goes off. The fuse that made the test light go off is the offending circuit. If a small draw..<200 ma, you may need the ammeter. G/L
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
You can do the same with the voltmeter but then you have to read it.
The bulb just glows.
Really you can do this with an ammeter since there shouldn't be any large current flow without something like a fan running or starting the motor.
If something is shorted the fuse would be blown and no power drain. Or a wire melted.... Your looking for a short but not that kind of short. A switch that is on instead of off.
Some meters still don't go high so take that with a grain of milliamps.
I have one that goes to 20 unfused but found out not all are constant use even if they go that high.
The bulb just glows.
Really you can do this with an ammeter since there shouldn't be any large current flow without something like a fan running or starting the motor.
If something is shorted the fuse would be blown and no power drain. Or a wire melted.... Your looking for a short but not that kind of short. A switch that is on instead of off.
Some meters still don't go high so take that with a grain of milliamps.
I have one that goes to 20 unfused but found out not all are constant use even if they go that high.
Racer
Joined: Jan 2005
Posts: 492
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From: Birmingham AL
Originally Posted by big_G
You can use an ammeter, but you risk killing the meter if you hook it up wrong or exceed the limits of the meter. Use a 12 volt test light in series with the load. Pull off either battery terminal. Hook 1 end to the terminal, the other to the connector. Any time there is a draw, the light will be on. Pull fuses till the light goes off. The fuse that made the test light go off is the offending circuit. If a small draw..<200 ma, you may need the ammeter. G/L
There is another way and that would involve a connection of one lead directly to ground. But that's NOT what you're testing. You are looking for small draws with the car OFF. Keep the meter INLINE with the battery terminal by removing the batt terminal from the batt and then put one lead of the meter on the post of the batt and the other lead on the terminal itself. Just don't let the terminal lead hit the gnd anywhere or again you will melt you're meter. The same is true of the light bulb method as well, you will blow out the bulb instantly if you do the same things. 
Race Director
Joined: Nov 1999
Posts: 10,643
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From: Foxfield CO 1970 Convertible
Originally Posted by steves_77vette
The same is true of the light bulb method as well, you will blow out the bulb instantly if you do the same things.
Racer
Joined: Jul 2005
Posts: 499
Likes: 1
From: Winnipeg Manitoba
Big_G's suggestion of a lamp is a good one for finding "leakage".
1) You can see it go on and off from a distance if your fiddling around.
As you pull fuses you can see which one is conducting current by the intensity of the bulb.
2) Its a potential short your hunting down, there could be big current if it turns into a dead short. Enough to kill a meter.
3) Your radio shouldn't need a kill switch. It off state current draw should be VERY low if its even 15 years old. (10's of micro amps)
4) You won't kill the bulb if one end is connected to battery plus and the other end gets shorted to ground. That's 12 volts, its a 12 volt bulb!
1) You can see it go on and off from a distance if your fiddling around.
As you pull fuses you can see which one is conducting current by the intensity of the bulb.
2) Its a potential short your hunting down, there could be big current if it turns into a dead short. Enough to kill a meter.
3) Your radio shouldn't need a kill switch. It off state current draw should be VERY low if its even 15 years old. (10's of micro amps)
4) You won't kill the bulb if one end is connected to battery plus and the other end gets shorted to ground. That's 12 volts, its a 12 volt bulb!
