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tomyboy67m2000
New User
Nov 5, 2011, 5:58 PM
Post #1 of 14
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Hi there, i have a 1990 dodge ram charger 150 it has a 318 motor. my problem, the the battery will not stay charged! i have a new alternator(oem) & a new battery, there are no running lights on or anything on to run battery down. i have checked battery while car is running with a voltage meter and it reads 11.75 it reads the same when car is not running. also the voltage regulator is internal i believe located in the bcm(computer). i have gone online to fine a bcm ( 200.00 dollars) should i replace the bcm?? please help! Thanks!!
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Hammer Time
Ultimate Carjunky
/ Moderator
Nov 5, 2011, 6:21 PM
Post #2 of 14
(1954 views)
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Re: charging system
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Don't replace anything until you have tested the system. A professional scan tool would be very helpful but you can find the dk green wire at the alternator and momentarily ground it while watching the voltmeter with the engine running. If the voltage spikes up, the PCM is the problem. If not, look elsewhere. Test the main fuse by checking for power at the main alternator terminal with the key off. If you have power, the fuse is good.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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tomyboy67m2000
New User
Nov 5, 2011, 6:52 PM
Post #3 of 14
(1947 views)
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Re: charging system
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thanks hammer time i will test and let you know!
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Discretesignals
Ultimate Carjunky
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Nov 5, 2011, 7:02 PM
Post #4 of 14
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Re: charging system
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The regulator is built into the SBEC (engine controller) and not the BCM.
One way to see if the alternator is even functional is to ground the dark green wire at the alternator connector for a few seconds while watching your meter connected to the battery with the engine running. This will full field the alternator and your meter will read 14-15 volts. Don't leave the alternator full fielded too long. Do not ground the dark blue wire.
If your alternator comes alive when the dark green wire is grounded, you need to make sure the dark green wire is good to the SBEC at pin 20 of the SBEC connector.
If the dark green wire is good, make sure the SBEC is sensing charging/battery system voltage on the red wire PIN 3 of the SBEC connector. If you have battery voltage on the red wire, more than likely the SBEC's regulator circuitry is the culprit. Make sure the SBEC's ground circuits are good at PIN 11 &12 light blue/red. Voltage drop the ground circuits to check excessive resistance instead of ohm checking (less than .02 volts) with the SBEC powered up. If that checks good, swap out the SBEC.
If your alternator doesn't come alive by full fielding, let us know.
**darn it...HT beat me again....**
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Nov 5, 2011, 7:15 PM)
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tomyboy67m2000
New User
Nov 5, 2011, 7:49 PM
Post #6 of 14
(1919 views)
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Re: charging system
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fuse test is good but not sure what the best way to ground the green wire, should i use another wire and ground it to the alternator bracket??
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Discretesignals
Ultimate Carjunky
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Nov 5, 2011, 7:49 PM
Post #7 of 14
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Re: charging system
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It took me 40 mins to find and read the schematics, compile the information, and write/edit that post. Getting faster...hehe 
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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tomyboy67m2000
New User
Nov 5, 2011, 7:51 PM
Post #8 of 14
(1915 views)
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Re: charging system
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thanks discretesignals.
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Hammer Time
Ultimate Carjunky
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Nov 5, 2011, 8:04 PM
Post #9 of 14
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Re: charging system
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You can either back probe the plug at the alternator or sometimes we use something called a "bed of nails" attached to a jumper wire. You can ground it on anything metal.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Sidom
Veteran
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Nov 5, 2011, 8:34 PM
Post #10 of 14
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Re: charging system
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I'll just toss this out real quick if PCM turns out to be bad. There is a bypass kit available that uses an external voltage regulator to keep the PCM from being replaced for charging system issues...
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Hammer Time
Ultimate Carjunky
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Nov 5, 2011, 8:40 PM
Post #11 of 14
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Re: charging system
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I have given instructions using an old 2 wire Chrysler regulator but I wasn't aware of a redi-made kit for that.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Sidom
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Nov 5, 2011, 8:58 PM
Post #12 of 14
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Re: charging system
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One of our suppliers use to have a kit they sold.........Pretty much the same as your instruction but it came with the reg, plug & wiring instructions........Been ages since I've had to do one............I'll google to see if there is a part # still available.........
This is a different brand but basically the same kit....
Conversion kit
(This post was edited by Sidom on Nov 5, 2011, 9:02 PM)
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Discretesignals
Ultimate Carjunky
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Nov 5, 2011, 10:09 PM
Post #13 of 14
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Re: charging system
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I never knew that existed or even thought of bypassing the SBEC. Learned another new thing today thanks to Sid.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Sidom
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Nov 5, 2011, 11:02 PM
Post #14 of 14
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Re: charging system
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I never thought about it either until I saw the kit for the 1st time.
That was always a fun conversation with the customer for the poor writers, telling them they need a new PCM cuz the alternator wasn't charging...
Those poor guys always take the heat for these manufacturing screw ups.......Like it was their fault.....
1st time I heard a writer tell a customer the 3 Bs I bout laughed my azz off
I didn't Build it!!! I didn't Buy!!!! AND I didn't Break it!!!!!!...........
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