Charging System Failure

[erik70rt]

I recently replaced the engine wiring harness in the Challenger and also removed some aftermarket gauges.  Now the charging system is failing and draining the battery.  I tested the battery and it was at 12.6 volts on my multimeter.  When I started the car, it dropped to 11.8 volts.  I had the alternator tested not too long ago and it was fine, but who knows now.  The alt gauge I removed were directly wired to the battery, so I did not take out any splices and such. 

It looks like a bad alternator to me, but thought I would ask to see if there are any other ideas before I go spending $$.

Thanks!

[Tunis]

What kind of alternator are you running? Internal regulator? Otherwise check your ground on your voltage regulator on the firewall.

[erik70rt]

Voltage regulator on the firewall is grounded ok. 

[RUNCHARGER]

Check the field wires attaching to the alternator.

[erik70rt]

The field wires are part of the new harness.  I have the blue lead attached to the lower terminal on the alternator and the green to the upper.  When I saw it discharging, I switched them to see if that was the problem.  No change. 

[1 Wild R/T]

There are three wires attached to your alternator... The big fat one, that should be 12V all the time... The small blue one should have 12v when the key is on.... And the green wire goes to the regulator & the regulator grounds it to cause the alternator to charge....  So... With the engine running unplug the regulator & ground the green wire while checking battery voltage.... Charging?  Check the regulator & it's connections.... Not Charging? Look at the alternator & it's connections.....

Regulator has two wires, the green one that goes to the alternator & the blue one which is keyed 12v power...  The regulator also needs a very good ground because A) it needs to be able to ground that green wire... And B) it uses the 12v from the blue wire & the case ground to reference your charging voltage.....

Alternator, cheat.. Run a 10 ga wire from the big post to the positive battery.. That eliminates the resistance from going through the bulkhead connector twice plus the Ammeter......

[erik70rt]

The 12V lead is hooked up properly.  I pulled the green wire from the regulator and ran it to a ground - no change.  So then I pulled the green wire off the alternator and ran a direct ground off of the alternator - no change. 

I'll pull the alternator and have it tested again. 

[1 Wild R/T]

Do you have 12v on the blue wire & the big wire? 

[erik70rt]

I have 12 at the blue wire and 0 at the big wire.

[1 Wild R/T]

And there you go.....  Either the two connections at the bulkhead connector or the two wires the attach to the ammeter.... You mentioned eliminating an ammeter, the wires from that need to be connected to one another..

The other option, run a 10 ga wire from the Alternator output stud to the battery stud on the starter relay....

[erik70rt]

That doesn't make sense to me as the ammeter I removed had a wire running from the positive terminal on the battery directly to the gauge, and the return from the gauge went right to the starter relay.  When I took it off, I ran a wire from the positive side of the battery to the starter relay per the wiring diagram.  The ammeter in the dash still works.

[1 Wild R/T]

Well humor me & add a wire from the Alternator output to the battery post on the starter relay...

[erik70rt]

I get 15.5 volts at the battery when I ran that wire.  Alt gauge in the car still showed a discharge as well.

[1 Wild R/T]

Well, the voltage regulator isn't seeing the voltage so it's full fielding the alternator looking for maximum output.... And the Ammeter doesn't see it either...  Take the bulkhead connector apart & check the two battery leads....   Cavities 16 & 18

16 is in the headlight harness connector, it's the big blue wire...

18 is in the engine harness it's black

They are the two big 12 gauge wires....

[1 Wild R/T]

Look at both sides of the connectors, I've seen more than a few times where the new harness had wires in the wrong cavity & if that happens with the main alternator feed you get what you have now....