'73 Charger not charging

[Triple Black 73]

I took the Charger out on Easter Sunday for the first time since November. It started to run really rough and the tach was jumping all over the place. So I pulled over and checked a few things. I found the battery had drained to 11.8 volts while the alternator was putting out 14.2v. I measured 0.5 OHMs between the battery post and the alternator post. I study the manual and checked the wiring and I'm lost.

What could be the issue? I can't confirm if I ever verified the charging system ever worked. However, both the alternator and voltage regulator are 20+ years old.

Also, at point in the near future I would like to upgrade to a 180 amp alternator, relocate two batteries in the truck, and add at least 2000 watts of speakers amps in the trunk. I want to do away with the ammeter and replace it with a volt meter. With that in mind what's the best was to upgrade the system?

 

[Triple Black 73]

Also, with the engine off, there was 12v at the battery and 10v at the alternator post.

 

[Triple Black 73]

Looks like the 0.5 ohms reading is enough cause the 2.3v drop. Great.

 

[YY1]

If you can't get it fixed, you will have to change the name of the car.

Couldn't resist.

14.2 isn't really enough, should be closer to 14.7 IIRC.

Quick test is to see if the car runs with the battery disconnected.

If not, something in the charging system is amiss.

Regulator is usually the first thing people suggest, but I've only ever had one bad one.

I've a a car eat diode in the alternator, and that gives a very slow, and hard to diagnose discharge condition.

 

[PurpleBeeper]

Here's my best guess....
1. Charging
a. At the battery terminals, you should get about 12V with engine off & 14+V with engine running.
b. It "sounds" like you have resistance in your factory wiring somewhere between the alternator & the positive post of the battery OR a really, really bad ground issue.
c. I suggest you clean your grounds really, really well (including the metal they attach to) - battery terminals, block, body & cable ends.
d. I suggest you track down your wiring problem, maybe disconnect different sections and check for resistance (meaning it's grounding somewhere). The bulkhead disconnect is a good place to start.
e. As a temporary fix, I suggest you run a big (2-gauge or 4-gauge) wire directly from the big post on your alternator to the positive post of your battery. TEMPORARY. fyi-I have mine setup that way with two 40-amp fuses in parallel to take the load off my electrical system with the amp meter still hooked up.
f. I'm not sure how to test them, but you "might" have a voltage regulator problem.... I just swap them out when I'm not sure since they are cheap.

2. Stereo upgrade:
-I'm no stereo expert, but your factory wiring is only designed to handle about 1/3-1/2 of that much power, so you might want to run a totally different, fused circuit, right off the battery (or batteries)....someone else on FBBO can help you more I'm sure.

 

[Triple Black 73]

Thanks man! Yeah, finding where this 0.5 ohms is coming from won't be fun to resolve. I think I'll pull two harness at the bulkhead and test across the black wire and red wire. That will let me pretty quickly if the issue is inside the engine bay or under the dash.

About the 4ga cable from the alternator to the battery, I will need to do that to run the amps. Do you also have the original black wire hooked up at the alternator? Do you have any fuses or diodes on it? I was reading that Mother Mopar ran 10ga cable through the firewall for fleet vehicle with 100 amp alternator

 

[Triple Black 73]

Just check the wiring on the car.

• Battery to starter relay (new 10ga cable) - 0.01 ohms
• Fuseable link (45 year old) - 0.05 ohms
• Engine harness plug to alternator (20 year old) - 0.03 ohms
• Red cable from fuesable connection through the bulkhead to black cable pin (45 years old) - started at 4.0 ohms settled at around 1.0 ohms.

Time to take at the instrument panel and test to the ammeter. Fun. But hey, don't we just love these old cars?

 

[rlem1977]

On the 'started to run rough and tach began jumping' - might be the coil, ballast resistor, or could be faulty grounds. Also, how old is the battery? I agree with PurpleBeeper, need to go over all of the wiring. That engine compartment stuff gets brittle from age and heat, can have strands broken that reduce effectiveness, plus other peoples mods and hack jobs. This stuff was never, ever, meant to be in service for 45 years.

 

[Triple Black 73]

The battery is a two year old 1000 cca red top optima. I think that's why i didn't notice the charging issue. It is overkill for the stock system since these cars came with a 300 cca battery.

I think I resolved it. For now. The red and black leads going to the ammeter was corroded and the nuts were rusted. I cleaned everything up with sand paper then put it back together. I tested 0.1 ohms from the alternator to the batter and 14.3 volts at the battery with engine running. Runs way better now.

 

[rlem1977]

The battery is a two year old 1000 cca red top optima. I think that's why i didn't notice the charging issue. It is overkill for the stock system since these cars came with a 300 cca battery.

I think I resolved it. For now. The red and black leads going to the ammeter was corroded and the nuts were rusted. I cleaned everything up with sand paper then put it back together. I tested 0.1 ohms from the alternator to the batter and 14.3 volts at the battery with engine running. Runs way better now.

It's not rust, it's patina!

 

[wyrmrider]

And removing patina ruins the antique value- do you not watch "Ann Tigues roadshow"
seriously do the wiring upgrades, ampmeter bypass etc B 4 new alternator
relay on the headlights- use the 5 prong one

 

[rlem1977]

And removing patina ruins the antique value- do you not watch "Ann Tigues roadshow"
seriously do the wiring upgrades, ampmeter bypass etc B 4 new alternator
relay on the headlights- use the 5 prong one

I agree on upgrades. Many want original, but new technology can bring increased reliability and efficiency, which translates to more enjoyable ride.

 

[Triple Black 73]

And removing patina ruins the antique value- do you not watch "Ann Tigues roadshow"
seriously do the wiring upgrades, ampmeter bypass etc B 4 new alternator
relay on the headlights- use the 5 prong one

Can you give more information and details about the ammeter bypass? The power windows and the 'batt' on the fuse block splices off the alt side of the ammeter.

As far wiring upgrade goes, the positive battery block is gold plated with two 4ga holes and two 10ga holes. I want to run a 4ga from the alternator directly to the battery (with a inline fuse) via one 4ga hole and the other one to 4ga/4 position fuse & distribution block with a digital volt meter that feeds the rest of the system. The 4 pos being: directly to the starter, the starter relay, fans/headlight relays, and the amps (when I add them).

The ground side is very solid. I ran a single 4ga off the battery to a 200 amp cut off switch that splits to a 4ga to the frame rail, engine, and to the core support that provides ground to the headlight, electric fans, and a factory ground location.

 

[rlem1977]

I believe you should not run from the battery directly to the alternator, fuse or no fuse. I have not seen an electrical diagram where that is depicted. Be careful, you could end up with a bigger headache.