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Weird Electrical Issue

15K views 12 replies 5 participants last post by  LeShadow 
#1 ·
First time poster here, and I am glad I found this site. I have a 2004 Elantra with about 68,000 miles on it. The car has never given us any problems until a few weeks ago. While driving down the road, the radio started cutting in and out, then the gauges, then the windows didn't work, etc... Got home parked the car, tried to start the car and discovered the battery was dead. So I figured the alternator was bad. I took the alternator out (thanks to help from this site) and went and had it tested. It tested fine. Charged the battery, put the alternator back in, metered the battery and everything was fine. The car battery was getting charged. Figured the problem was just something loose that I fixed putting the car back together.

One week later, I metered the car while running before heading on a trip and the battery was being drained. So this time I took the battery to get tested and it was fine.

So...anyone have any ideas?
 
#3 ·
Hey ! Bienvenue !!!

- Remove the Neg wire from the pole and look at the AMP drain. U should have something between 0.040 Amp and maybe 0.080 Amp.
More than that, u have something draining the battery.

- Verify if the ALT is giving u 14V.

- Verify the wire and the terminal on the ALT.
Personally, I had to change the wire from the ALT to the Battery Pos pole on My J2, with a similar issue... Upgraded for 2AWG wire !
:D


Hope this will help !
 
#7 ·
The wires look good, everything looks fine, which makes this all the more confusing. Looking in the Haynes manual, does anyone know where the 'excitation resistor' is located?

Looks like there are also some fuse links between the battery and the alternator. Does anyone know where these are located? I guess just somewhere in the shielded cable between the alternator and the battey? Has anyone blown one of these?

I had a fuse link go bad on another car I had. Took forever to figure it out so I am always skeptical of them.

Thanks for ideas and help!
 
#8 · (Edited)
Alternator fuse is the 120A fuse in the fuse box under the hood. Think 120A was for the 90A alts, and 100A was for 80A alts.

Pre-excitation resistor is on the back of the interior fuse box. (Top row right, second from the right) The Pre-excitation resistor is used to start the charging process in the alt. If the alt fails to charge, your battery indicator light should be on. (battery icon in the gauge cluster)

Does the voltage increase on the battery when the car is running from when the car is off? If so the charging system on the car is fine. It's the battery not holding the charge.
 
#10 ·
While the car is running, it is pulling juice from the battery. So if the battery is like at 12.7, when it runs it will be at 12.3. The battery is about a year old, and I took it to Autozone and had it tested along with the alternator and both tested fine. Cables look good, so it has to be something strange. I did check all of the fuses with a voltmeter (just checking via the tabs on top of the fuse) but I should probably pull them out and inspect them closer, especially that pre-excitation resistor fuse.
 
#11 · (Edited)
When it runs, the reading should be something like 14V.

Take booster cable, connect one on the ALT, and the other one on the POS pole of the Battery.
By that way, u'll see if it's a cable failure somewhere.

If Still 12V, disconnect the POS from your car and Connect the Pole on the pos of an other car. Start the second car. Y still should have 14V.
 
#12 ·
Well, took it to the dealer again, and they swore it was the alternator. Took the car home, took the alternator out and took it to Napa and it failed on the 'pre light test', before it even started spinning. At Autozone, I don't think they test as well as Napa (if I am wrong let me know). So got a new alternator at Napa, cost 140, with a 3 year warranty and things seem fine now. All the drama and it was just the alternator the whole time. Thanks for all of the tips.
 
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