[xtreme2own]

hey guys! first post here. looking for a few answers,

I have a 1990 Mustang GT 5.0 and i purchased last week. When i bought it the guy had a brand new in box alternator for it, and said that, that was the reason the check engine light would illuminate about 30 minutes after normal driving. I took it to a shop (before purchase) and they said that the trouble codes were not listed in the computers memory. So, i bought the car, thinking it would be an easy fix.

I bolted in the new alternator. Put in a new optima battery (800CCA, 1000 CA). After four days, the battery amps on dash kept getting lower and lower, until today, when it actually would not start. My question is, what could this be? Where should I start? What should I look for...

Some things that have changed in the past few days:

Ive installed, pullys, including alternator pullys. I dont believe that this would lower the charging ability to where it kills the battery however. Especially when im not running a big stereo system.... yet..

New alternator. There are three wires to attach. You must cut out the harness and hard wire it, per aftermarket alt. instructions. There are three wires, a small white one, and two bigger black ones with orange stripes. I got the white wire right, but when connecting the two black ones i MAY have mixed them up? Instructions said just to connect them.... giving me the impression it did not matter.

The refurb alternator i purchased may be bad? Lifetime warranty so i doubt it.

These are the things ive changed. Also, the car had a rigged electric fan that is wired funny and needs to be cleaned up a bit. I plan on taking it to a shop but maybe you guys would know where to start touble shooting this issue? Or give me some ideas of what may have gone wrong?

Let me know, thanks in advance for all the help!!

[TheUNZippee!]

Load test the battery and test the alternator. Just because it's a new alternator doesn not mean it can't be defective. Start with those basics and go from there.

[superman5.0]

do you think it might be the electric fan and the pullies? and might need bigger altinator? i am doing these upgrades soon and wandering if i will need a bigger one

[neverfastenough1]

What amp is the alt.? Zip is right about the just because its new thing. If I had to take and uneducated guess (because I am so uneducated it ain't funny), I am going to have to go with the fan. Depending on which fan it is it could be drawing a lot of power at start up and frying the alt.. I would check all that funny wiring. If you can tell me how it is wired I can educatedly try to help figure out if it is right. Also, check all your connections for corrosion and looseness. A bad connection will cause it to not charge properly. I will do some research on the alt. in a few, but gotta go rebuild a helicopter right now. Also, check the cables for bulging or cracks. Bulging is an indication of corrosion.

[superman5.0]

my altinator is stock ampage

[TheUNZippee!]

And ud pullies cetainly affect alternator output. By the very nature of how the ud's work, it's reducing the output of the alternator.

[superman5.0]

yea i got that, so should i just forget the pullies? i havent baught them yet but i was about to in about an hour.

[TheUNZippee!]

Personally? If you are going to be running a serious stereo system, which you seemed to hint about in your other post, I would forget them. I have a large stereo in mine, and it draws over 150 amps alone when it's cranked. I wouldn't think of putting ud pullies on. I'd rather get those few horse somewhere else.

[skid6]

check the grounds

[04silversnake]

I think it is the electric fan. My 91 Gt as soon as I installed the electric fan, it did not charged the battery. If I shut the engine off, there would not be enough charge to restart. I switch to a 130 amp alternator from a SN95 from Autozone and problem solved. Hope this helps.

[Tony_90fox]

i just got done with the same problem..I thought it was because i added a "few" things..so i put another ground on the other cylinder head, put a new ground on the driver side as well, and cleaned up the battery cables...Helped a bit...

If you have underdrives, just put the stock pulley back on the alt...I had to get a new belt (83.5" without smog and stock alt pulley)...Charges AMAZING just with the stock alt pulley on...

Trust me, my car would run fine, go to start it and nothing....Change to the stock alternator pulley and tell us what it does.

[JBIGBOOTSY]

electric fan+pullies+alot of idleing+stock amperage alt=bad battery drain

[patwrecked]

i dont have underdrive pulleys or an electric fan and at idle with my lights on the volt meter is at ten and the rpms start getting a little lower

[Tony_90fox]

Did you put the volt meter on the battery at idle, or is that 10 on the gauge?...Either way, that is WAY too low...

Make sure all the lights are off...Visor mirror lights are bad for that!

Clean up the battery cables..The stock battery ground cable is LONG....Try getting a 36" cable to shorten it up some.

Check the ground at the back of the driver side head...Replace that and see if it does anything...Also, add one to the passeger side.

See if that helps any.