Battery light / idle voltage

Yellow00Stang · Jun 15, 2023

I have a 2000 GT that has had the battery light on since I bought it 1.5 years ago. Got it checked out at Ford when I bought it. They said the electrical system checked out fine and it could be the aftermarket alternator. Drove until a couple of weeks ago and battery died. Alternator seemed to be issue per check at auto parts store. Replaced alternator with 130 amp instead of lower amp one installed. Also replaced battery as it was dead also. Battery light now kicks off just over 1700 RPM but comes on below that. At idle I'm still only reading 12 to 12.5 V. I have the Mach audio system and saw a thread on the amps creating a drawl on the battery. Pulled both plugs on amps but still same voltage. Have cleaned up battery terminals and ground connections. Alternator wire was spliced also. I cleaned that up with butt connectors. What am I missing? Corrosion somewhere? Fuses? Appreciate and thoughts or ideas.

07GtS197 · Jun 15, 2023

If you hold the throttle open to where the battery light turns off, what voltage is it at? I don’t think it’s a wiring issue since it sounds like it charges just not at idle. Do you have underdrive pullies?

Yellow00Stang · Jun 15, 2023

07GtS197 said:
If you hold the throttle open to where the battery light turns off, what voltage is it at? I don’t think it’s a wiring issue since it sounds like it charges just not at idle. Do you have underdrive pullies?

Still at about 12.1 to 12.2V. Not certain if it has underdrive pulleys or not. I haven't put any on if it were stock. Bought it off of a flipper who got it from the grandson of original owner. I don't think he drove it long or did much to it after he got it from grandpa. Car had 56k when I found it so I suspect much of it is stock. Only thing noticeably aftermarket was wheels, exhaust, and some interior billet hardware. Made me wonder if it had them though when I saw the light disappearing with the increased RPM.

07GtS197 · Jun 15, 2023

Yellow00Stang said:
Still at about 12.1 to 12.2V. Not certain if it has underdrive pulleys or not. I haven't put any on if it were stock. Bought it off of a flipper who got it from the grandson of original owner. I don't think he drove it long or did much to it after he got it from grandpa. Car had 56k when I found it so I suspect much of it is stock. Only thing noticeably aftermarket was wheels, exhaust, and some interior billet hardware. Made me wonder if it had them though when I saw the light disappearing with the increased RPM.

I’d have this alternator tested too. It doesn’t sound like it’s working. And make sure the harness is plugged in and the pins are making contact.

cobrajeff96 · Jun 16, 2023

General advice is to stay away from the insulated crimp butt connectors and do a direct solder, ideally with heatshrinkable solder sleeves.

Yellow00Stang · Jun 16, 2023

cobrajeff96 said:
General advice is to stay away from the insulated crimp butt connectors and do a direct solder, ideally with heatshrinkable solder sleeves.

When I bought it, one of the previous owners had installed a new alternator plug. They had it installed by just twisting the wires around each other and throwing electrical tape on them. I figured the crimp butt weld connectors couldn't be too much worse than that Was being lazy on the soldering. I wouldn't think that would be shorting anything still using them but could be wrong. I'm definitely no electrician.

Yellow00Stang · Jun 16, 2023

07GtS197 said:
I’d have this alternator tested too. It doesn’t sound like it’s working. And make sure the harness is plugged in and the pins are making contact.

Yeah I plan to get it all checked out again. This is actually a new one I put on from American Muscle just yesterday. I did have a 105 amp O'Reilly Auto Parts one on there when the previous one failed. When the battery light was still on, I upped to the 130 amp. Forgot to mention that originally. The 105 amp kept the battery light on regardless of rpm so I saw some other threads noted going to higher amperage.

07GtS197 · Jun 16, 2023

Yellow00Stang said:
Yeah I plan to get it all checked out again. This is actually a new one I put on from American Muscle just yesterday. I did have a 105 amp O'Reilly Auto Parts one on there when the previous one failed. When the battery light was still on, I upped to the 130 amp. Forgot to mention that originally. The 105 amp kept the battery light on regardless of rpm so I saw some other threads noted going to higher amperage.

I’ve read about those alternators being bad right out of the box. It seems that alternators for these cars are hit or miss in general. If you can find one, an 05+ p71 alternator is an upgrade and is I think 200 amps but has a bigger case so fitment can be an issue.

ttocs · Jun 17, 2023

Is that the stock pulley for the alt or do any of them look like they were replaced with under drive pullies? They are normally aluminum and look a little cooler than the stock pullies and can cause voltage problems.

As mentioned above uninsulated crimps are not good outside of the car/under the hood. It is probably better than what you had, but still not good enough.

Yellow00Stang · Jun 20, 2023

Problem solved! Was going down the list in the fuse box and came across an empty slot labeled "Generator". Popper a new fuse in, battery light gone, charging at 14.1 volts on the posts and 14.2 coming off the alternator!! Very glad this wasn't a grounding issue. Not sure how I drove a year and a half without a fuse in the generator port without having issues sooner. I found the missing fuse sitting two blocks down in a spot labeled for "A/C pressure 3.8L only". It doesn't even allow you to connect in. It was just sitting there. I'm assuming last owner moved it there temporarily or something and forgot to put it back or maybe pulled it and didn't know which place it went back to. Who knows....back in business though!