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1976 M880
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Discussion Starter #1
Hello all! I've read multiple posts about wiring in these vehicles and have had much success in tracking certain problems but am at a standstill. I bought this truck from a fence row and after it had sat for 6 years previous rotting away. I figured for 300 it wasn't a no brainier. After a new starter and fresh fuel I drove it home and began to bring it back to roadworthy condition. I did the amp bypass, ditched the ballast resistor since no points ignition. New BBD carb, new 100 amp alternator and voltage regulator. I replaced the starter relay and all battery wires with 2/0 gauge I use on all our heavy equipment. Overkill but it's not going to fail me. I ran the same gauge wire for grounds such as Neg to frame, frame to head and head to frame. Alternator is also grounded to frame with same gauge wire. Voltage regulator is grounded with original ground strap and a 8 gauge wire from Neg terminal on battery. Alternator puts out 15.8-16.7 volts to battery. I pull green field wire off and it goes to battery voltage 13.2. Pull off red wire and goes to 13.2. I checked ohms on voltage regulator ground and it's .02. Battery voltage is 12.8 at the red wire terminal on voltage regulator plug and connections seem right. Everything is packed full of dielectric grease. One more problem is ignition switch harness is a complete hack job. The only wires present is big yellow and a small orange. It starts with the key but firewall harnesses are in poor condition but there. My questions are 1, Why after all new parts it's still over charging? Lots of big grounds and all mating surfaces are polished and covered in grease plus battery protection spray. #2 is how would I know if the previous owner connected the wires correctly using crimp connectors? I don't have to use a factory harness and have no problem soldering them together but, what colors connect to what? I can see how and why it had a melted amp, gauge cluster. Trying to preserve it considering it has all it's records and documented 64,379 miles. Any and all help is very appreciated. I plan to use this in a veterans day parade hopefully next year providing the pandemic is under control. Thank you!
 

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One thing that I learned is that the aftermarket voltage regulators are up to par. I had the same problem with a few VR's. I found out about an adjustable one. Tried googling to find the part number and BAM found this YouTube video! He's got the part

Here's a screenshot.

Watch the video and you'll see the adjuster on the backside of the VR.
Brian
Screenshot_20201017-183415_YouTube.jpg


Sent from my SM-N960U using Tapatalk
 

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My suspicion is that if you're getting 16 volts out then your voltage regulator might not be working at all. You sure is isn't shorted or somehow bypassed?
 

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1976 M880
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Discussion Starter #4
I received an adjustable voltage regulator from alternatorman and installed it today. Voltage is at 15.2. I traced the ign wire from regulator plug in and disconnected it and jumped straight to the positive side of the battery. Voltage is at 14.3 now. I noticed a little wire on side of the radiator support and ran a jumper from Neg terminal to radiator support and the difference is very noticeable. Battery voltage is at 12.3 not running and believe it to now be a bad battery since I had it trickle charge for a week. With the key on and not running, voltage at factory compression splice at ballast resistor is 11.2. Voltage regulator is reading .02-.03 ohms even after another firewall cleaning and two grounds, one strap and the other a 10 gauge wire to negative terminal. Not exactly sure what I am doing, but a digital multimeter is worth every bit of money. Thank you for your patience and look forward to suggestions!
 

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I received an adjustable voltage regulator from alternatorman and installed it today. Voltage is at 15.2. I traced the ign wire from regulator plug in and disconnected it and jumped straight to the positive side of the battery. Voltage is at 14.3 now. I noticed a little wire on side of the radiator support and ran a jumper from Neg terminal to radiator support and the difference is very noticeable. Battery voltage is at 12.3 not running and believe it to now be a bad battery since I had it trickle charge for a week. With the key on and not running, voltage at factory compression splice at ballast resistor is 11.2. Voltage regulator is reading .02-.03 ohms even after another firewall cleaning and two grounds, one strap and the other a 10 gauge wire to negative terminal. Not exactly sure what I am doing, but a digital multimeter is worth every bit of money. Thank you for your patience and look forward to suggestions!
15.2 is high, but not dangerously high. Cold weather will cause voltage to rise on these old mechanical regulators. I've seen old cars hit 15 under very cold conditions. If your battery is really bad, the charging voltage might be being pulled higher than normal by the high current load. Just a theory, but at this point I'd try a new battery. Another possibility is that something is just wired wrong. 14.3 would be a very normal running voltage.
 
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