# Ohms

Because I can turn my blinkers ON with the key OFF in my 1997 chev. pickup, I have been wondering if there is a electrical draw on the battery. I disconnected the negative & positive leads from the battery. I tested for Ohms between the negative lead & the positive lead. It read 0.00. I also flipped the meter to milivolts, staying in the Ohms selection. It also read 0.00. Is that test worthy? Does it prove that I do not have an electrical draw on the battery?

It read zero or infinite? If it read zero, I think that means it’s a short and will suck up power. To find electrical draw you need an ammeter that you run in the completed circuit, including the battery. It will tell you how many amps or milliamps are running in the circuit while off.

I won’t take time to explore what you are doing to your meter but just put your meter on amps and put it in series with the negative battery terminal and the negative battery cable. You may want to put a real low value fuse in this circuit to protect your meter (the fuses for my Fluke DMM are over 10.00 each). Ohms and milivolts don’t come in play when looking for a draw, its amps, and of course some amps will be flowing if the light is blinking.

Does your meter have a 1 amp position? How about 500ma? (1/2 amp). That’s where to start. What YEAR is your truck? When they started putting computers in them (81??) there will always be a little draw, 50-100 ma.

If your multimeter reads 0 ohms resistance between the negative and positive terminals, you either have a dead short, or Ohm’s law was repealed as part of the new health care legislation. Since there seems to be quite a bit of resistance to the new health care bill, my guess is that you aren’t on the correct scale of your multitester.

Reading the resistance between the positive and negative cables is completely invalid and tells you nothing. Testing for current drain, as suggested above, is the way to check for this problem.

No, he doesn’t have a dead short. Due to the fact that the ohm meter only sources a very tiny amount of current, and the electronics and capacitors in them are reactive, you will get a false reading of nearly zero ohms. This is the same reason that the battery cable will spark a little bit when you first connect it. A rush of current flows to charge the capacitors in the electronic modules and to initialize the units. After the brief start up surge, the current falls off. After another ten to thirty minutes, all the electronics go to sleep and the current should fall to less than 0.05 Amps.

Yep, it tells you nothing of value, the OP simply is using his meter wrong, this is not so hard to correct.

Checking for a short this way is like measuring the ocean by staring at it from the beach.

Use the 10-amp range on your meter, making sure you connect the leads to the meter in the correct ‘holes’. Put the meter in series with one of the battery leads. Do NOT open the car door, use any electrical accessories/turn the ignition on while trying this test. If you get less than an amp drawn, you may CAUTIOUSLY use the milliamp range on the meter. (reconfigure the leads) I’d guess that more than 300mA (.3 of an amp) at rest and you are running the battery down.

But a better test is—does the battery run down when the truck sits for a few days? On any car, you can run the hazard flashers with the ignition off. They wouldn’t be very useful if you couldn’t. Turn signals though? Unusual. I wonder if someone rewired the system.

The test is not meaningful.

let’s get to the real question. Have you been having indications of a parasitic drain? Has your battery been draining overnight? Or is this simply a learning adventure you’ve set out on (not a bad thing at all)?

The test is not totally invalid or meaningless. It’s far too complicated to be used in any qualitative manner, but quantitatively, there is some merit. The easy example is the one in which the car in question is one that you know, along with the typical resistance between hot and ground battery leads (disconnected battery). If the reading is very different from what is typically seen, all else equal, then a problem exists. Likewise, if the Ohmmeter shows just an Ohm or two across the entire harness for more than a few minutes, you likely have a problem. As was mentioned, there’s a lot of capacitors in the electrical system, but there’s also inductors (and resistors) in parallel. This all works together to reach a number that should change, at least slightly, and has no relevance whatsoever in an absolute sense due to the complexity and uncertainty of the system, unless it stays exactly at zero ohms, which would likely indicate an immediate and very dangerous short. I agree it’s not a very useful test, especially in relative terms, but not sure it deserves the disdain everyone has for it. Lol