I have a 1987 Dodge B-150 318 V-8 and I have a charging problem.I replaced the alternator and the voltage regulator and had the battery tested for dead cell which it was fine and recharged . I ran the van for one day no apparent problems until that evening . Went to start and battery did not have enough cranking amps to turn engine over. Any ideas ?

Did you replace belt?Is it tight enough?Do you have fusible links?Check alternator wiring,may need replacing.Check battery,old alternator could of made it bad.Check ground battery cable,follow it's other end that is screwed into block.Also check positive cable to starter.Did you have the old alternator tested?Unlikely new alternator is bad.

Did you replace the voltage regulator?

The way to check for an over or under charge is to connect your volt meter to the battery, before starting the vehicle.
You should have a reading of 12.5 to 13 volts. If it's 11.8 like you stated or less, it means battery is not fully charged, or it's bad. Now start the car & check voltage again while running the engine, the voltage should exceed 14+ volts, this means your Alternator is charging, the voltage should drop after battery has been charging for awhile. When you turn the engine off after letting it charge the battery, & if the battery is good, you should now have 12.5 volts to 13 volts.
Now to answer your question, the Voltage Regulator is inside of the Altenator, I believe you xcan take the alternator apart to replace it, or simpler to just replace the complete alternator.

I'm going to assume your meter is accurate and you have verified the 18.4 reading.
Something has to be bypassing the regulator to make the alternator charge at full power. The regulator breaks the circuit dozens of times per minute to maintain 14 volts. Does the alternator charge with the regulator unplugged ?

Bad voltage regulator. Usually built-into alternator.
Start car and unplug battery, if it dies your alternator is dead. Get new alternator. If car keeps running, get a voltmeter and check voltage coming through - should be higher than 12v but less than 18v. Any other number means your voltage regulator is dead, cheaper to get a new alternator.

Go through few Alternator related solved Solutions including replacement of alternator.Select and Click the link below:----How to replace alternator? http://schematicsdiagram.blogspot.com/2011/12/how-to-replace-alternator-on-gmc-sonoma.html
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How to test alternator on Dodge Stratus?

http://technoanswers.blogspot.in/2012/02/how-to-test-alternator-on-dodge-stratus.html

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How to test and replace Alternator on Audi A4 Car models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-test-and-replace-alternator-on.html

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How to Remove Voltage Regulator on Car?

http://vwrepairhelp.blogspot.com/2011/11/how-to-remove-voltage-regulator-on-car.html

HOW TO REPLACE AN ALTERNATOR BELT

http://schematicsdiagram.blogspot.com/2011/08/how-to-replace-alternator-belt.html

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How to monitor Vehicles charging system? http://repairhelpcenter.blogspot.com/2011/11/how-to-monitor-vehicles-charging-system.html

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Car Alternator making noise? http://repairhelpcenter.blogspot.com/2011/11/car-alternator-making-noise.html

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After replacing Alternator, the battery indicator light Comes ON dash?

http://howtobyme.blogspot.com/2011/11/after-replacing-alternatorthe-battery.html

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How to inspect Vehicles Alternator?

http://repairhelpcenter.blogspot.com/2011/11/how-to-inspect-vehicles-alternator.html

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How to Test Vehicles Alternator?

http://repairhelpcenter.blogspot.com/2011/11/how-to-test-vehicles-alternator.html

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How to Service Vehicles Alternator?

http://repairhelpcenter.blogspot.com/2011/11/how-to-service-vehicles-alternator.html

How to Replace Alternator? http://repairhelpcenter.blogspot.com/2011/11/how-to-replace-alternator.html

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Alternator testing? http://schematicsdiagram.blogspot.com/2011/12/alternator-testing.html--------- Cars electrical system is pulsating? http://technoanswers.blogspot.in/2012/01/cars-electrical-system-is-pulsating.html------ 1998 Ford F150 pickup Battery Drains overnight due to Alternator? Alternator drains car battery? http://technoanswers.blogspot.in/2012/02/1998-ford-f150-pickup-battery-drains.html------- 2002 Ford Focus sits over night and battery goes dead? http://technoanswers.blogspot.in/2012/02/2002-ford-focus-sits-over-night-and.html--------- Charging system problem on Chrysler LHS car? http://technoanswers.blogspot.in/2012/02/charging-system-problem-on-chrysler-lhs.html---------- How to replace alternator 1997 Dodge Stratus? http://technoanswers.blogspot.in/2012/02/how-to-replace-alternator-1997-dodge.html------- How to replace Alternator on Mitsubishi Lancer http://www.howtorepairguide.com/2012/10/how-to-replace-alternator-on-mitsubishi.html
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These details will help.
For more help.Keep updated.
Thanks.
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the amperage of the alternator is immaterial as long as it is big enough to run the electrics of the vehicle
what is indicated here is that the new alternator required an external voltage regulator or a properly operating regulator to regulate the output voltage
battery voltage in a new battery fully charged is 13.2 volts dc and when the voltage regulator is working the controlled voltage is 14.5-14.8 volts dc
check how you wired up the alternator and have an accredited to test the charging circuit

You need to bypass voltage regulator to be certain alternator is charging properly. When you full field alternator it eliminates voltage regulator. If it indeed is good it will overcharge. If it overcharges as it should when you bypass/full field alternator then the regulator, or its connection or the place it attaches to is rusty & wont conduct a ground.

Check your battery and check the ground wire from battery. Make sure all your wires are clean and good connections. A bad battery will not charge and a dead battery will not charge a alternator maintains a battery not charge a battery, so charge your battery completely before checking that the alternator is working. Check all the wires going to the starter for good tight and clean connections . Hope this helps...

Have you actually tested voltage output with multimeter, as this all happens ? May need new alternator to start with, it has voltage regulator built in I believe.