My son’s 69 is draining the battery when it sits. Sometimes this can happen over night. Sometimes it stays charged for days. Had the alt checked it’s OK but the drain problem continues. I’ve gone through 3 batteries. Any ideas?
Dave, You can disconnect the negative battery cable and take a 12 volt test light and hook one end to the battery cable and stick the pointed end in the negative battery post or hold it there with your son's help.
If the light goes on you have a drain.
If the light is off verify the test light is good and hooked up correctly (good contact) by turning on something on like the parking lights. The test light should glow.
If he has a radio that requires a 12 volt power source all the time (for a clock or station presets) you will have to disconnect that wire because that will light the test light.
Now that the test light is hooked up and illuminated and everything you can see is turned off as far as you know, start pulling fuses one by one to isolate which circuit is causing the draw. The light will go out when there is no load on the circuit and that will be your battery drain.
If the fuses don't turn the test light off you may have to start disconnecting wires.
The brighter the test light is the heavier the load (drain) is.
This test will also work on computer controlled cars but there is a milliamp draw from the PCM so the test light will illuminate but it will be dim.
99' GMC P/U
69' Camaro X-11 350/T350,AC,PS,PB, 12 Bolt
96' 17' CC KEY WEST w/85 Yamaha (has shark fins on the sides like the 69')
First check all of your grounds for good contact. If they are all ok then the problem may be time consuming to track down (eg lots of tracing wires and checking each circuit with a voltmeter). Most likely it is a short in a component or circuit.
I had a similar problem that seems to have stopped since I capped some cut wires hanging loose under the dash. Somebody (or several somebodies) butchered my dash harness for radios etc. and didn't bother to cap or tape up anything. I think there was a drain from one of the uncapped wires.
You can also test for a draw by disconnecting the battery cable and putting a multi-meter in line. Set it on amperage. You shouldn't have much more than 15-20ma for a radio memory. Any more than that you have another problem. Start pulling fuses till the drain goes away to isolate the problem circuit. Remember to hold in the interior light jamb switch so you don't have a false drain.
If you use the multimeter on the amperage scale be careful. I have the Fluke 77 & 88 DVOM and the fuse rating is only ten amps. I believe Sears Cratfsman has a DVOM that is 20 amp fuse protected. You could blow the fuse in your meter, check your meter before using. A blower motor for example can exceed a 20 amp draw.
Well I finally got around to doing all the ideas posted and none of them worked. But I did unplug the Alt. Thinking that it may be the diode and the trouble light dimmed a lot but not completely out. So I unplugged the Voltage reg and the light went out. Any Ideas?
By the way the car has been in storage with the cable disconnected as my son drives the car and he went off to school so we haven’t been driving the car. However we took it out of storage last week and alas a new battery had to be put in. Sears is getting a little leery about giving us another one.
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