What is wrong with my electricals?????!!!!!


Asked by Jul 19, 2015 at 08:20 PM about the 2008 Ford Mustang V6 Premium

Question type: Maintenance & Repair

My 2008 mustang 4.0 v6 pony/premium
packages has electrical issues and I can not
for the life of me figure it out. My
headlights, map lights, and tag light will
flicker. My subs (2 kicker twelves on a 250.1
mono class D amp) will cut out. And my
blower motor resistor (Controls the speed
on the A/C) will blow. This happens when
coming to a stop or sitting still at idle. Never
while on the pedal. Alternator overcharges
(up to 17.6 volts at times) and will spike
causing my battery needle to shoot to max
when slowing to a stop or at an idle in park
or drive, and one of the symptoms I listed
above will happen. Normally it's my A/C will
speed up like I turned it on high when it's
only on 2 and the speakers will cut out. I
pulled my aftermarket stuff out of the car.
And I still have the same problem. So I
know my aftermarket electronics are not
the cause. I have tried adding an extra
ground cable (8 guage) from the alternator
to the negative battery terminal thinking
maybe that would help. I read about the
ground on this forum on another thread,
that's why I tried it. It didn't solve anything.
Still happens. Can anyone shine some light
on what may be going on? Any ideas are
welcome. I'm so stumped as to what it
could be. I will try just about anything at this

10 Answers

Bob Beaman

Have you replaced the alternator?


I have replaced battery and alternator multiple times. Doesn't change a thing.

Bob Beaman

You running 1 battery or 2?


1. But I don't forsee that being an issue. I'm thinking more pcm or ground issues honestly. With the way it acts. It's not draining my battery. Nor killing my battery. Just spikes randomly up to 17 volts for no reason

Bob Beaman

I would disconnect the aftermarket stuff and run the car for a few days to see if the problem goes away. The high voltage the alternator is putting out is causing the issues, but it is necessary to find the cause of the alternator overcharging. Usually it is the voltage regulator, but nowadays the regulator is most likely part of the alternator. Please post what the cure for the problem is when you find it.

1 out of 1 people think this is helpful.

Will do..


Put everything stock back in the vehicle. Have drove it for a few weeks now. Same problem still persists. I will keep updating this with what I tried and what failed. If anyone has any more input please let me know. I will try just about anything at this point. I am to the point of where I'm about to order a new pcm and a new smart junction box to see if this fixes the problem.


A lot of these alternators the interior of them built in China. Have a bad diode. Will check well at the store but inside you have a bad electronic. Some people have gone through 3 or 4 Alternators to get a good one. China builds terrible interior electronic systems on their Alternators, new or rebuilds! Also check your grounds. Make sure all grounds are ok. Or you may have a parasitic drain. Mustang radios are noted to not shut down. They drain constantly. I bought a JVC radio, no drains. Made sure Alternator was gone through by a great electronic mechanic. No problems at all. I also replaced all slow box fuses to make sure they shut down after 5 minutes. Replaced all bulbs.


I am about to try having a guy around here that does great rebuilds do an alternator for me. I'm working on checking all my grounds and connections. I have already checked the easier ones. And they seem fine. It almost acts like the belt is slipping with the way it's spiking. I don't have dead battery problems. So the drain isn't an issue with mine personally.


Your SJB, smart junction box, is corroded. This is caused by a clogged drain under the cowl which allows water to pool in an area above the SJB. The cowl is the area between the engine & the cabin.

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