Alternator not charging battery (HELP)

cthalite3 · Jul 1, 2015

I have a 70 Roadrunner I named J.R. (not junior) with a mild built 440(wasn't matching numbers when I purchased so I did a pro touring look)with a lot of mods. Music, Halo lights, HID lights, etc. I had my factory alternator rebuilt to 200 amps. I have a battery for the car and a battery(both in trunk) for the music but for some reason the alternator is not charging the battery. I have a 4 gauge hot wire running from both batteries to back of alternator. I have replaced the regulator twice and just replaced the ballest resistor. I know the regulator is notorious for going out on a regular but is there a way to eliminate the regulator and ballest resistor? I'm sure i'm missing something but I have to start somewhere. Is there an expert out there that can help?

GetX'd · Jul 1, 2015

Sometimes it's as simple as tightening the belt. What else have you tried....?

cthalite3 · Jul 1, 2015

bought new battery, tested alternator, checked for loose connections. changed regulator, changed ballast resistor. found out the ballest resistor was .8 so guy at auto parts store said the biggest he had was 5 ohm. that's about it.

resq302 · Jul 2, 2015

First, I would start by pulling the alternator and bringing it to a place to test it. If that tests out good, I'd back track the wiring as maybe there is some corrosion in a connection somewhere which isn't allowing the power to go the way it should.

Hemi Rebel · Jul 2, 2015

The ballast resistor has nothing to do with it.
You need to check the voltage at the field terminal at back of alternator. How much voltage is being supplied to the field circuit? You can test the alternator yourself, its called full fielding.
Dont over think this. The alternator is simple. The field citcuit is 2 wires. Power in, and ground. Current flows through and it makes electricity when its spinning.

PurpleBeeper · Jul 3, 2015

Yeah, I'd have to vote it's a field wire. It should be 12volts. It's probably not the 4-gage power wire, but you could check continuity and short to ground just in case. The last thing would be a good grounding (alt/block, block/body, body/frame, etc.) which can be a PIA sometimes, but you could start by cleaning the ends & attachment points for all the grounds. Bench testing the alternator is a good idea to for sure....that's about it. Good luck!

Icecobra · Jul 3, 2015

Your going to hate this but two batteries tied together will discharge just sitting there. They have had this problem on diesel engines forever. Get a battery isolator this would help you bunch in the long run. Your right now problem as stated check the alternator if it is working then move to testing field wires and grounds etc. You could also to answer your question eliminate the regulator and buy a single wire alternator and you can get them pretty cheap nowadays.. Check fitment and look for things like where everything comes out the back and make sure its not going to hit any connections after installation. You did not state what kind of ignition you have electronic aftermarket etc.. If you have aftermarket ignition you can eliminate most everything down to hot wire to distributor and coil and one wire alternator would clean it up nice. No need for resistor, regulator, field wire this cleans up wiring a ton...

gtxno1 · Jul 4, 2015

check that big red wire that goes to to the bulk head connector they burn once in a while and to the gauge that gauge must operate for the system to charge

383man · Jul 5, 2015

Is the car charging at all ? Have you put a voltmeter across the battery to see what the charging voltage is while its running ? Also make sure the larger wire on the alt which is the main hot wire that it charges the battery through is hot all the time. In other words with the car not running and the key off not on make sure the large wire on the alt is hot and has 12 volts all the time even with the key in your pocket. If its not hot all the time it may have a fuseable link bad. Ron

Alternator not charging battery (HELP)

cthalite3

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GetX'd

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cthalite3

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resq302

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Hemi Rebel

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PurpleBeeper

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Icecobra

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gtxno1

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383man

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