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Car dies when lights are switched on

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kayosfrawg

Proven Member
47
1
Feb 8, 2013
Gainesville, Florida
I have been having a problem with parasitic drain from the electrical system for months. It has been running fine as long as I drive it everyday, and when I go out of town or don't drive it for a few days I stick a maintainer on it and it works well. However today was a little different.

I started the car, after checking voltage since it has been about a week since I ran her, let her run for a minute then switched on my lights, and immediate death. I switched off the lights started her again and drove her around for a bit to charge the battery back up. Pulled into the driveway and turned on the lights, again died immediately.

Have you guys heard of anything like this before? Any clues where I should start to look? This is a new one for me.
 
I would say the alternator is going out. Do you have a power steering leak by any chance? It is very common for the ps pump to leak on the alternator and ruin it. When mine went out I was still able to drive it, but any sort of electrical draw would make the idle drop and the car want to die.
 
If the alternator is shot, the battery will drain so low without the possibility of recharge and thus killing the battery when put under a greater load!
 
Take a multi meter and measure battery voltage with the car off. It should be around 12.6V (6cells-2.1v each). If its any lower than, or even around, 10-10.5v, replace the battery.

Then, with the car running check voltage again. With the car running you should have around 14v, some cars are around 13.5, some around 14.5. If its not within .5v of 14v, then replace the alternator. This means the voltage regulator has gone bad and can no longer supply the proper voltage to the battery to maintain a charge.

I recently had a problem that I noticed becuase my radio would shut off while accelerating and would come back on around idle. Well, my voltage regulator was bad and was trying to charge at over 18v.
 
If you want you can swing it by your closest autozone or advanced. They can do a free in car battery, starting and charging test. It will check cranking amps and voltage in the battery as well as starter draw amps, voltage regulator, total output, and diode ripple. All with one machine. I would then check grounds. 12v DC needs a continuous path in one direction to be able to charge. If there are missing or corroded ones it wreaks havoc with stuff. Ive even seen corroded grounds be responsible for taking out the ECM. Electricity takes the path of least resistance. Lastly, theres no aftermarket anti-theft system or alarm in it is there? Ive seen similar symptoms if the wiring to do with one of those goes teats up...
 
OR you have a short in the lighting circuit since it dies when you turn them on. Does it die when you just turn the dash/taillights on or when the headlights on? Remove the relay for that one to see if it still dies (to help identify where the short is).
 
Just a small note if you have an AGM battery (like an optima) voltage isnt a reliable way to tell if they're bad. An Optima can be discharged as low as 1.5v and still be able to take a full charge just fine. Mine was down to below 8v and charged back up just fine. Just in case you have one ;)
 
Okay the battery did need to be replaced. I'm taking the alternator in to be tested as soon as I get back in town. I'll let you guys know what happened next weekend when I am back. Thanks so much for all the replies.
 
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