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I recently acquired a 1979 dodge ram 150 from a family member. I have been plagued by a charging problem. The batter consistently charges at 11.88 volts DC. The alternator puts out around 20 or so volts DC. I've replaced the alternator twice, and same for the Voltage Regulator. For the life of me I cant find what could be causing the problem. Any help would be greatly appreciated. Thank you.
 

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Try bypassing the ammeter.  Also, check the connections at the bulkhead.
 

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The bulkhead is the harness connectors on the firewall where they pass through.  A very common place for corrosion on the terminals and therefore, resistance.
 

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You can disassemble the connectors or there are some spray electrical cleaners that do an ok job.  Mostly I use trimmed pieces of emery board fingernail files or sandpaper wrapped around a small flat bladed screwdriver.  Once clean, pack the connectors with dielectric grease to prevent future corrosion.
 

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Matthew853 said:
I recently acquired a 1979 dodge ram 150 from a family member. I have been plagued by a charging problem. The batter consistently charges at 11.88 volts DC. The alternator puts out around 20 or so volts DC. I've replaced the alternator twice, and same for the Voltage Regulator. For the life of me I cant find what could be causing the problem. Any help would be greatly appreciated. Thank you.
If you're putting out 20 volts at the alternator, you do not have a charging problem, you have a power transmission problem (the current isn't reaching the system). 11.88 volts means no charge is reaching the battery, that is the voltage of a drained battery.

Make sure you have done the ammeter bypass correctly. Then, install a large gauge wire from the alternator charging stud to the battery positive. You will now have a working system if everything is as you've described. Test battery voltage with engine running, and it should be about 13.5-14.5 volts. Let us know if it isn't.
 

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'79 Macho 360 Magnum, Comp 480 cam, Hughes springs, 650 Thunder AVS, Pertronix Flamethrower ignition
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Matthew853 said:
How would you clean the corrosion off of the prongs in the connectors? I doubt I could get a wire brush or anything to get the corrosion off.
You can use a tiny flathead screwdriver or pick and gently scrape the terminals to get a clean contact. It's tedious work but works well especially when nothing else does. Plus, make sure that "New" alternator is good. Just cause it's "new" doesn't mean its good. And check the wire and connector at the alternator and the wire that runs to the firewall. The wiring junction (bulkhead) is a problem area especially if an amp gauge bypass was done as the alternator wire passes through there. If a melt down has occurred it usually melts the plug and heavily corrodes the metal connectors at the junction (bulkhead) also. Use dielectric grease on all contact points to help prevent future problems. And if you or someone has done a bypass, make sure you run the proper gauge fuseable links on both new wires going in and out of the firewall. You don't want to burn down your '79!
 

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Placing your multi meter leads at the battery posts revealing the 11.8 vdc is the most telling part of this. Corrosion within battery cables is common and can cause a voltage drop. As stated before you should have a large gauge wire from the alternator positive shunt to the battery positive terminal. Dodge used the bare minimum gauge wire for grounding IMHO. That being said the easiest way to determine where the issue is as follows. Using jumper cables place the negative cable  on the negative terminal of the battery and the other end to a known good engine ground. Check your battery voltage. If acceptable replace the ground cable or add another. For the positive side, hook to the positive post and to the charging shunt on the back of the alternator. Ensure it doesn't ground out or you will have larger problems. Check your battery voltage.  If acceptable then remove just the ground side and recheck. This will isolate a bad cable.
 
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