Need help with my 66 mustang

auto electrician test for power drain would have saved you lot of money than guessing and replacing parts

bad ground.

check for faulty ground wire both chasis ground and engine ground for damage looseness and corrosion

03 Mustang GT (Parasitic) Battery Drain Fix

Hello,
I am seeing a lot of mustangs are having battery draining issues and I wish to share some simple solutions found while working on a friends 03 GT 4.6ltr.

In a quiet area, key switched off, hood up, Listen carefully close to alternator. I heard a high pitched hissing/whistle sound at low volume, came from back of alternator. This sound was the voltage regulator/rectifier staying on when key is off due to faulty diodes inside the voltage regulator/rectifier circuit, can cause battery to go dead after car not ran in about 2-7 days.

After having the alternator tested free at a parts store, test showed alternator was good because the faulty diodes in the alternator did not show up on the test, the machine did not test for faulty drain back issues that were present.
Alternator on-car-fix:

There was battery voltage running at all times through the two-wire connector on back of alternator. Disconnect the battery first for safety and to reduce chance of short circuit. The yellow wire/with white stripe is hot while car is off so I traced this from the 2-wire connector on the alternator then closer towards driver side front fender. Next I cut the Yellow/White Stripe wire, spliced a good connection wire to it and ran it through a hole in the fire-wall to the fusebox(under dash), connected it to a 15a fuse that does not get used but has power when key is turned on but no power when key is off.

The purpose for re-routing the hot wire to the alternator, is to turn off the alternator charging circuit when the key is turned off so it may not run down the battery. I am seeing good results with this fix(or patch) so far. No More Parasitic Battery Drain!

Another fix can be to change the small pulley on the alternator to a larger pulley so the alternator does not spin too fast, putting too much energy through the diodes can cause a charging system to act a fool. So if you have charging issues and have an alternator changed, putting a larger pulley on can make sense turn into saved dollars(especially on high revving engines).

I hope this info helps to solve some draining battery and/or alternator issues.

for reading,

TyBorg1

There is a voltage draw from your battery while engine is not running.to prove this loose any one of your terminals.with all switches turned off including engine, disconnect and re-connect the loose terminal.if you get a spark then there is a voltage draw, find the wire and replace it

Either you have an open wire somewhere that needs to be taped off, or your leaving something on. ALSO your alternator could be overcharging your battery B/C your voltage regulator is out on your alternator. I bet thats what your problem is. To fix, you have to tear your alternator apart, and replace the regulator in it, or just replace the alternator itself. Hope this helps, James Booth Please Rate This :)

The voltage regulator is built into the Alternator. Take out the Alternator and have it
tested at your local Auto Parts store (they all do it free). This will tell you if the Alternator
is your problem or if you need to check elsewhere.

It's called a CVR, constant voltage regulator, to keep all gauges with same voltage all the time, regardless of spikes. They seldom fail. I did not think we used one back in 66, but I did not start working for Ford until 1975. I would replace it and seee what happens. Let me know.

battery no good??? check the voltage regulator it may have fried the battery

Check the Battery and Connections. Not a lot of Guess work on the Old Mustangs. You may need to Clean the Cables to the Battery, Could be a Little Corroded. Please rate my Response, I need all the Help that I can get! Thanks!