Battery / electrical problem

[Save-A-Horse]

Put a new stereo in. Everytime the turn signal turned on the stereo would cut out (MP3). I have a 5.0 from 87'stang w/ fuse panel. W/ multimeter the radio circuit was definitely being affected by turn signals (dipping down to 9V). I found a stable circuit and wired stereo to that. Did multiple short trips and no problems. Took 'er out for a longer ride...battery died. Put the battery on charger overnight and for 4-5 days of short trips no problems. Took 'er out for a longer ride last night same thing happened...dead. Tested battery and alternator and both tested good.
Any ideas guys? Thanks-

 

[Save-A-Horse]

More detal: lots of corrosion on the positive terminal. I recently replaced my ignition switch. But that was done after noticing that the stereo was being affected by the turn signals. Could the corroded connection be my issue? It seems like I wouldn't be able to start it if that were the case...

 

[Viperwolf1]

Corrosion is never a good thing. Get it taken care of quickly. Sounds like the battery is not getting charged. Did you have the alternator removed and tested or was it tested in the Bronco? If it was removed you might have some wiring problems that are keeping it from working.

 

[Save-A-Horse]

Corrosion issue is addressed. Alternator was removed and tested seperate as well as the battery. I checked to see if something was draining the battery when off and there isn't. I also measured Voltage across terminals when off and it is about 13.6V. When I start the engine the voltage accross the battery terminals drops to 12.5V. I have under-driven pulley so I assume that could be the reason for the lower V. ??? Or maybe that is another clue... no idea. I think I may need to go for another drive and test it out now that the corrosion is gone.

 

[RRRAAAYYY2]

Under drive pulleys actually take more power away by reducing your voltage at idle, than they save in hp required to turn them. I would put a stock crank pulley back or get an alternator designed to be able to charge a lower rpms.

The 13.6 and then dropping ot 12.5 is an indication the alternator is not turning on at idle. But since you have 13.6 your battery is getting charged. If it is on a battery charger, then I would think your alternator is simply never turning on while you are driving. If tests fine off the truck, then I would think it has a wiring issue not telling it to turn on in the truck. What alternator is it?

If you are not putting it on a battery charger, then your alternator is likely turning on, just not charging at lower rpms. Bigger crank pulley or smaller alternaotr pulley should fix that.

 

[Save-A-Horse]

You were right RRRAAAYYY2, it turns out the ignition switch contact to the alternator had become disconnected. Since connecting it back up the issue with my battery being run down is fixed. However, like you said the under-driven pulley is running the alternator pulley a little slower causing lower run-Voltage supply to the battery.
Thanks for the feedback!

 

[Save-A-Horse]

Question: Would a high output Alternator (130A) solve my issue with my electrical demand which is caused by the underdriven pulley setup?