I'm looking for suggestions on the next place to look to track down a drain on my battery. The car is '31 roadster with sbc / alternator. I put in an EZ Wiring harness and had no problems for a couple of years. Now my battery drains with a few days of sitting. I pulled the negative cable and connected a multimeter from negative terminal to the now disconnected negative cable. I get a constant negative 12V on the meter. When I hook up a test light to the same setup, I get a a very short and fairly bright light and then the bulb dims to nothing. When I touch the light again immediately, I don't get anything to light up. Back with the multimeter hooked up, I pulled one fuse at a time and the meter constantly showed the 12V draw. Another symptom that may or may not be relative: I charged the battery up to 100% and the car fires right up. I shut the car off and then started it over and over for maybe 6 to 8 times. Every time she started up fairly quickly. After 8 times of starting, I put the charger back on the battery and she was reading 50%. That doesn't seem normal to drop that quickly. Any suggestions folks? thansks
if the test light goes out and stays out, you dont have a draw. using a volt meter will mislead you. try a fused amp meter inline of the battery cable, that will give you a much better idea of how much of a draw is on the system. it does sound like a bad battery, one bad cell will drive you nuts. also, a bad alternator can cause a battery draw, and they arent fused.
Check the caharge rate at an idle...If it is low but increases with engine speed you likely ahve a bad diode allowing an unblocked path to ground. The alt will usually buzz a bit when running due to the bad diode. Voltage will increase a bit with the rpm, but not enough to charger the battery, only drain it. I also agree that a battery test is in order...a weak or shorted cell can do the same thing. Hope this helps.
I had a friend that could not find a short after many hours of looking. He disconected the Batt., Radio and alternator and then applied 110V. to the batt. cables. In 5 sec, he found the short! (It was in a connector that was under a wet soggy floor mat) Do not try this at home Do not try this on my car I will deny all knowledge of this post in a court of law.
I would bet on a bad cell in the battery. You can't go by a voltmeter because a low current draw will still show 12 volts. You would need a milli-amp tester to check or a good quality test light. The fact that the test light goes out shows that any draw goes away.
because with the meter in line you'll always see 12 volts (it's reading the whole system), you need to use the amp settings. 50mA draw is ok for an older car. testing for current draws but it sounds like you have a weak battery that holds a good surface charge.
I have found symptoms like you are getting. when you hook a load to it will show full voltage, [brite bulb]for a second and then the small amount of heat [current]will make it find a resistance connection and then show [weak bulb]. Could be a battery, diodes, dirt, moisture, connections, lotsa things,-- batteries will do that, with internal weak connection.
it will always show 12v or whatever is left in the battery, it's the current that is the drawing of power.
IMO, just the fact that the bat goes to 50% so quick [volts prob under 11?] makes me suspect of the battery..
Charge up the battery,disconnect the positive cable,let the car sit overnight and see if the battery holds the charge. Really sounds like a bad battery.As far as the 110v to a 12 volt battery,damn thats just plain ass dumb and even dumber to admit it.
There is a difference between a short and a draw. A short will let the magic smoke out. A draw will drain the battery.Less than 30 ma is normal. I would still test the battery first then the charging system. Start with the basics before you start really digging.
"As far as the 110v to a 12 volt battery,damn thats just plain ass dumb and even dumber to admit it." Although I find it interesting, and wouldn't do it, he connected to the battery cables, not the battery.
pull the fuse on each circuit one at a time and retest,as soon as you see no draw thats the circuit that has a short
i was at A-Z looking for the smoke the pro's use. treir motors and cars run great, until the SMOKE gets loose.
How old is the battery? Does the car sit for long periods? You need an ammeter in series with a battery terminal and the cable to check for current draw. Clocks, radio memory, will draw bugger all. Brake ligths (poorly adjusted at the pedal) glovebox lights, luggage space lights, usually are the suspects of current draw. If the alternatoer is suspect, disconnect it, and try the tests again. You say after a few goes at starting, the power fades away. This sounds like an old battery that has sulfated, where it can only hold a surface charge. Get it charged fully, then load tested. Alternator diodes mostly will only stuff up if some idiot gives you a jump start and buggers up the polarity between the 2 cars.
bad starter...? had a issue with my chevelle, where it would show 12 volts till you started it ....if you didn't hit it on the first or second try , you were done. charger would let it hit after a while. volt gauge would show 12 volts till you hit the button , then it went to something like 10 or so. even with the alternator charging , it still wouldn't show much past 12....
The best way is to check the draw with an ammeter. Should be less than 50 ma. There is nothing a voltmeter can tell you when checking for draws. It does sound like it may be the battery.
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