OK, here goes, am trying to find a current draw in my '49, and in my searching found that the dome light always has 12 volts going to it, even with both door switches disconnected. There are 2 wires going to the dome light and one of them is hot all them time....is this suppose to be happening, or am I just needing to be shocked back to reality? I have not done anything with the wiring related to the dome light since I put in the wiring harness years ago....
I'd ***ume that the door switches connect to ground when the doors are opened, this completing the circuit. A fused hot lead goes to the dome lamp.
Yuppers, most of the older rigs used door and the manual switch on the light as the connection to ground rather than them being on the "hot" side Meaning that when the door is open and the ****on on the switch is out the switch makes connection to ground, When you flip the switch on the light you connect to ground or when you turn the headlight switch all the way over it grounds the light on that last click. That means that the wire to the light is hot all the time.
If the dome light is off with the doors closed you do not have a problem with that circuit. Start pulling fuses and see what circuit causes a draw. Then go over all the wiring for that circuit.
OK, Thanx for those answers, thought that's how it worked, but can't find any other draw at this point so had to blame it on the dome light.....oh well back to work....
Remove the ground cable from the battery, place a test light from the cable to the terminal. If it lights up, there's a draw. Rig the light so you can see it and start pulling fuses until the light goes out. Don't forget to check the alternator/ generator and an electric choke if you have one. Which should be wired to key on anyway.
Alternator? Stereo keep alive memory? GPS? Yes, I said alternator, I’ve seen alternators cause a parasitic draw. I’m guessing your battery goes dead overnight?
Multimeter on 10A scale in between neg cable and neg battery post, with key off, door closed, pull fuses one by one (reinstalling after each one) until you meter drops to an acceptable level. Once you find out what it is trace the circuit. Don't forget to unplug the Alt or Gen/Reg depending on what you have. Lastly, if your meter shows no draw you can load test the battery.
If you have an electrical center, fuse box, you can quickly check for a current draw by measuring the voltage drop across the fuses. With everything turned off, and a digital voltmeter on the voltage scale, place the leads on each side of every fuse, one at a time. Any fuse that has current p***ing through it will have a reading in millivolts (0.001). Ones without current p***ing through will read zero. The fuse that gives you a reading is the circuit with a draw. Note that if you have a modern radio it will show a current draw for the memory, but very, very small.
Good method, ***uming the draw is going through a fuse. Could be backfeeding through a bad alternator too, for example.
You have not said how much the draw is. If you have any electronics (audio system etc) they draw from the battery continously, its tiny but still enough to get a little spark when you disconnect a battery terminal. Other permanantly live circuits can be lights, horn, hazard lights etc, but these are switched so should not be drawing current in the off position.
Before chasing your tail, have an Autozone, etc test the battery. My daily would hold the charge I gave it, be dead the next day, still showed around 13 volts. Battery was only 6/7 months old. Charged it up, drove it to AZ where I bought it, guy came out with this little handheld thing, clipped the leads on and about 30 seconds later said “yes, battery is shot, holds a surface charge, won’t take a load”.
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