66-67 Dodge Charger Source Guide

Stop light / Flasher Circuit

Posted by Don Dodson on 0/24/05


Posted by Harry on 07/24/05  :

I have a 67 charger and when I apply the brakes at an idle my charging system drops  from  13.7 volts  down to around 11 volts.  
The charging system works  fine,  has  a  75 amp  alternator  with the newer style elctronic voltage regulator,  I can turn on my headlights, stereo, and electric pump all at the same time and my voltage barely drops at all, so it seems the  alternator is charging well at  idle speed.    I'm assuming there has to be some kind of short in
the brake light circuit  but don't see  where or how???    The car does have a new  rear electrical  harness  from Year One and all connections appear to be installed correctly.    
It's especially bothersome while driving at  night causing  the  headlights and dashlights to dim really bad at a stop.     


Posted by Don on:  07/24/05

If you look at the emergency flasher part of the schematic, you will see that the emergency flasher uses the same components to blink the rear tail lights in addition to the front parking blinker lights.  When you press on the brake pad, the stop lamp switch bypasses the emergency flasher blinker, and 12 volts goes straight to the turn signal switch and from the turn signal switch it goes to the rear brake lights.  Remove ALL of the rear brake light bulbs and then see if the voltage still acts the same way by going to 11 volts with the engine running.  You are trying to isolate to where the problem is located.  In any case, with the car
at idle speed, the voltage regulator should regulate the voltage to around 14.7 volts at the battery + or - .7 of a volt without any load seen by the charging system. 
Pressing the brake pedal shouldn't cause the voltage drop you are experiencing.  You have 6 lamps in the
rear brake lights and the current required for those bulbs is nil for what the alternator/regulator will see.  I have a 67 Charger and my system is the stock system that came on the car, and when I press the
brake pedal, the ammeter immediately reacts by the needle dropping toward discharge, and recoving toward a charge condition.  That is the regulator kicking in and providing the charge condition as the system sees the load from the 6 stop lamps coming online.  You will need to use some common sense when removing the rear tail lights and testing your system.  If the discharge still occurs, then the turn signal switch is in the middle of that scenero.  You just might have a shorted tail light lamp in your system that can create your
condition, and this tactic would find that fault.

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