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Discussion Starter #1
Hello again. :(

New random issue started the other day.

When I accelerate, volts drop and battery light goes on... When I stop accelerating and just continuing at a even pace the volts regulate and light goes off.

I got a quick vid with my iphone.
‪Voltage decrease‬‏ - YouTube

Any idea what could cause this?


Thank you


(v6 supercharged with vortech v1)
 

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Any Check engine DTC's?

Any Belt slipping (my front runner vote).

Have you had the alternator tested for correct output and excessive AC ripple?

Are the battery terminals clean, tight, and corrosion free?

Is the battery strong and holding a charge?

Check the ground strap from the motor mount to the frame rail.

Also suggest measuring the battery voltage with a proper volt meter. The cluster gauge is not accurate.
 

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Discussion Starter #3
Belt is tighter than a 12 year old...

I cleaned the terminals....

if i accelerate hard the volts go back up haha but if its just a general acceleration they dip until i come to a steady speed (rpm drop) so the belt does seem like the most likely...

car hasn't died or stalled due to this, and the car doesnt seem to be acting different at all even... so im not sure
 

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It sounds like either the alternator is bad or the alternator is not getting a good voltage reference. This could be from a dirty supply connector or ground.

Take it to your local autoparts store and have the alternator tested for correct output and excessive AC ripple. It's free. Don't waste time looking for a problem unless the alternator is tested and known good.

Check where the battery cables connect to the main battery box in the engine bay. Ensure that the stud is clean and tight.

Check the small electrical connector on the alternator. Is the connector clean and tight?

The cluster is grounded at G203. G203 is located behind the center console. G203 is shared by multiple devices including the radio. G203 is frequently messed up during a radio install.

Measure the resistance from cluster pin#2 (BK/W) back to battery negative. Should be low. Post.

The cluster voltage meter is driven from I/P fuse 15. Put a VOM meter on the R/Y circuit from I/P fuse 15 so that the voltage can be monitored while driving. Trying to confirm that the voltage is actually changing.
 

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It sounds like either the alternator is bad or the alternator is not getting a good voltage reference. This could be from a dirty supply connector or ground.

Take it to your local autoparts store and have the alternator tested for correct output and excessive AC ripple. It's free. Don't waste time looking for a problem unless the alternator is tested and known good.

Check where the battery cables connect to the main battery box in the engine bay. Ensure that the stud is clean and tight.

Check the small electrical connector on the alternator. Is the connector clean and tight?

The cluster is grounded at G203. G203 is located behind the center console. G203 is shared by multiple devices including the radio. G203 is frequently messed up during a radio install.

Measure the resistance from cluster pin#2 (BK/W) back to battery negative. Should be low. Post.

The cluster voltage meter is driven from I/P fuse 15. Put a VOM meter on the R/Y circuit from I/P fuse 15 so that the voltage can be monitored while driving. Trying to confirm that the voltage is actually changing.
I know this is an ancient thread, but what is G203.. and what should one look for?

My mustang is having a problem (1 week after installing a Ipod fm modulator, wired into the cigar lighter) that the Alternator is only putting out 12.8 volts max.

I uninstalled the FM modulator completely, but still having the same problem.
 

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Varnco, what about all the "other" very good tests called out in this thread? Have you done any of them? What were the results?

Trouble shooting isn't like a book. You can't just skip to the last chapter. It rarely works for everybody.

Trouble shooting works best when you "follow the steps".
 

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I just messed with the radio, installing a fm modulator, and then this problem crept up... just figured they were related and a good place to start.
 
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