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Discussion Starter · #1 ·
Another electrical gremlin for ya’ll.

Reminder, I have a 1978 W200 with 440.

A few months back I replaced my alternator due to mine not charging. At the same time, I took superburbans advice and added a dedicated charge wire that ran straight to the battery to take the load off the dash.

Well my alternator seems to be charging at 15.4 volts and my battery boiled over. Is this a problem with the alternator? Or a voltage regulator? I thought the voltage regulator on the firewall cut voltage going to the coil down or something similar, and has nothing to do with the charging system correct? Is there a second voltage regulator?


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Did you run the wire from the alternator straight to the battery, or did you run the wire straight from the regulator to the battery?  You can't bypass the regulator on the firewall unless its an internally regulated alternator.  The regulator has a lot to do with the charging system, it makes sure the alternator cannot overcharge the battery and boil it over.
 

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Discussion Starter · #3 ·
Straight from alternator to battery. I had another thread a while back where my aftermarket voltage gage was bad and one thing led to another in the discussion and one of the things reccomended was to run a 10 gage wire direct from alternator to the battery to take charging load off of the amp meter in the gage cluster.


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I would not run it that way, you will kill your battery and alternator.  When trouble shooting you can run a wire from the alternator straight to the battery to see if you alternator is bad.  The regulator regulates the voltage in your system. 
 

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the heavy wire off alt IS a battery + positive wire , 2 smaller wires = 1 is hot only when key is ON the other goes back to regulator , yer overcharging ? is either a bad or an un-grounded ( AT ITS bolts ) regulator .
running the heavy wire straight to battery is a good thing and has NOTHING to do with how much the alt puts out .
 

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Ditto.

Over charging, can be a few things. Bad regulator, bad ground at the reg, bad ground between the body and engine, or even bad battery ground.
 

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Well, I learned something new today.  ::)
 

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Discussion Starter · #8 ·
dodge82273 said:
the heavy wire off alt IS a battery + positive wire , 2 smaller wires = 1 is hot only when key is ON the other goes back to regulator , yer overcharging ? is either a bad or an un-grounded ( AT ITS bolts ) regulator .
running the heavy wire straight to battery is a good thing and has NOTHING to do with how much the alt puts out .
This is the way I understood it the first time. From what I gathered from the FSM, it seems I have a grounded out field wire. It seems you all think the same, am I reading these replies right?

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15.4 volts is not a grounded field. That would put out 18+ volts. You have either a bad regulator or resistance in the regulator circuit. This makes the regulator think system voltage is lower than it actually is and starts increasing voltage to make up the difference.

You can try a new MOPAR brand regulator. Do NOT get ANY aftermarket regulators - they all suck now.

To check resistance problems, pull off the regulator plug and test voltage (engine off). Compare this to battery voltage (engine off). Ideally it should be within 0.1 volts, but realistically up to 0.3 is alright. At 0.5 or more different, you will see overcharging by the same amount.

Also check the regulator to firewall surface and make sure there isn't rust/corrosion reducing a proper ground.

Look at the harness connections on top of engine heading to the alternator and along firewall for corrosion of the terminals. If your voltage is off despite clearing all of those, you have to check the connections under the steering column and then consider a failing ignition switch.

All this assumes you have the ammeter bypass. The ammeter in pre-81 trucks is a serious failing point. Although the wire straight to the battery should reduce this risk.
 

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W200'78 said:
Another electrical gremlin for ya'll.

I thought the voltage regulator on the firewall cut voltage going to the coil down or something similar, and has nothing to do with the charging system correct?
Nope.
Your confusing the voltage regulator with the ballast resister.
The ballast resister is the one that drops the voltage to the coil after the engine starts.
 

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Discussion Starter · #11 ·
KurtfromLaQuinta said:
Nope.
Your confusing the voltage regulator with the ballast resister.
The ballast resister is the one that drops the voltage to the coil after the engine starts.
Ok. Thanks for the clarification.

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Discussion Starter · #12 ·
ToxicDoc said:
15.4 volts is not a grounded field. That would put out 18+ volts. You have either a bad regulator or resistance in the regulator circuit. This makes the regulator think system voltage is lower than it actually is and starts increasing voltage to make up the difference.

You can try a new MOPAR brand regulator. Do NOT get ANY aftermarket regulators - they all suck now.

To check resistance problems, pull off the regulator plug and test voltage (engine off). Compare this to battery voltage (engine off). Ideally it should be within 0.1 volts, but realistically up to 0.3 is alright. At 0.5 or more different, you will see overcharging by the same amount.

Also check the regulator to firewall surface and make sure there isn't rust/corrosion reducing a proper ground.

Look at the harness connections on top of engine heading to the alternator and along firewall for corrosion of the terminals. If your voltage is off despite clearing all of those, you have to check the connections under the steering column and then consider a failing ignition switch.

All this assumes you have the ammeter bypass. The ammeter in pre-81 trucks is a serious failing point. Although the wire straight to the battery should reduce this risk.
I have not done a full ammeter bypass. I have bypassed the factory ammeter but did not drill out the bulkhead connector because mine is perfectly fine. Figured adding the charge wire straight to to battery and physically bypassing the ammeter, I would alleviate those problems.

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W200'78 said:
I have not done a full ammeter bypass. I have bypassed the factory ammeter but did not drill out the bulkhead connector because mine is perfectly fine. Figured adding the charge wire straight to to battery and physically bypassing the ammeter, I would alleviate those problems.

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As long as your bypass wire stays intact, it will work. The only risk would be if your bypass wire ever came loose or burned out etc, all the current would revert back to through the ammeter again. Maybe not likely, but a risk nonetheless. If the bypass wire is the only wire, any failing and you'd know it by loss of voltage/charge.
 

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W200'78 said:
The ammeter is not connected at all.

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then you're safe there. Either your regulator is going or you have resistance in other places as mentioned previously.
 

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Discussion Starter · #16 ·
ToxicDoc said:
then you're safe there. Either your regulator is going or you have resistance in other places as mentioned previously.
Appreciate the help. It'll be this weekend before I am able to mess with it any. These 12 hr work days eat up alot of free time. Ill update what I find when I get a chance to do some checking.

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Discussion Starter · #17 ·
I got a few free minutes to do some tinkering. I bought a new mopar voltage regulator, ground some paint off the back of it and some off the firewall to make sure it grounds good. I tested for voltage at the voltage regulator plug and got nothing, well like .5 so basically nothing. But the plug itself is not in the best shape, and I discovered one of the terminals was broke inside while I was messing with it so that is probably the cause of the no voltage. So now I am waiting on a new voltage regulator plug to arrive. Rock auto had them in stock for like $5.


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one pin of reg gets and sends to 1 field terminal ,  battery voltage when key is ON , the other pin GIVES an amount of ground TO the other field terminal ,around 7 volts worth ,  about 1/2 of what it wants alternator to PRODUCE .
 

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The plug has 3 points - one has no terminal btw. The other two should have one receiving power from a switched source and the other is the return from the alternator.
 
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