90 Mustang GT voltage/wiring troubles?
 

So here we go...
I have tired myself for the past 3+ days trying to figure out the problem. First, let me start off by saying that I just recently (last week) tore my whole dash apart and did all that happy stuff evolving a new heater core, so if that info helps...here we go.

My car died just recently and I thought I just exhausted the battery on the car trying to fix and tune some stereo and miscellaneous parts on the car. I figured it would be a good investment to by a good battery, so I did. After the new battery installation, I ran the car for a while to see if everything was ok. It wasn't, my battery gage was around 12 volts and testing the battery with a volt-meter, it was running at about 11.5, and the gage wouldn’t really move at all when running the car. I thought it was a bad connection with the wires behind the instrument panel. I tore the IP apart again and checked the connection, which was good. So then I thought it was my alternator. I took my old one off and inspected it, and it caught when it was spun freely in a small spot. I thought what the hell, I should get a good alternator for the car too, so I bought a new one (which I kind-of regret now cause the old one tested fine). Hooked the new one up and still the same results as before. So then I went and tested all the connections on the alternator, battery, coil, and found nothing out of the ordinary. I also tested all the battery cables, wires to and from battery and alternator. I replaced the pigtail coming off the alternator thinking corrosion was the cause of the bad voltage, and still, the same results.
I am running out of ideas...and help would be greatly appreciated!!

Hey man dont feel alone because i am have the same problem, mine seems like it kills the battery when i drive it, but i too posted about this ame problem so maybe one of us will get an answer soon

when the flashers are on my battery gage goes up and down with every click of the lights if that helps at all...i've tried pullin fuses to locate the draw and it didnt help

...and it never did it before the heater core transplant...it would run in the 14's-15's

Do you have a wiring diagram for the car? My roommate had and 83 that didnt charge. Replaced the alternator still had the same problem. Found a wire had burnt at the starter solnoid. Check for charging voltage on the back side of the alternator. Where the wire connects with a nut. If you have power there keep following that wire back until you see 0 volts. If you dont have power at that wire at the alternator you have a bad alternator. Also do you have a ammeter or a voltmeter on the dash? As far as the gauge dropping with the lights flashing that is normal. Every older ford i have ever been in does it.

yes, i have a repair manual with LOTS of diagrams. did his car die after sitting a while?

are you talking about the two screws on the regulator on the altenator?

in the dash there is a volt meter.

it never dropped when the flashers were on before...say it were normal...should it drop a volt or so and back up?

His car died after sitting for a unknown amount of time. Ran okay for enough time to clean the cats out of it after he bought it. The posts on the alternator . Should be stamped B post. It will also have the biggest gauge wire running to it.

sorry for the quality of the pics...all i have is my phone for pictures....

i was wondering what these two wires were on the left side of the steering column behind the dash...they are black with a white tracer
http://c2.ac-images.myspacecdn.com/i...ec66c5f3f1.jpg
http://c3.ac-images.myspacecdn.com/i...a0a0914df6.jpg
http://c3.ac-images.myspacecdn.com/i...a7844af942.jpg

i also was wondering if anyone knew what this was? it is behind where the radio would be and i am thinking of a slight chance antifreeze leaked into/onto it?
http://c1.ac-images.myspacecdn.com/i...5120ba67e4ce98
http://c2.ac-images.myspacecdn.com/i...dbf5e1ac71.jpg
http://c2.ac-images.myspacecdn.com/i...83bc3fd471.jpg
http://c4.ac-images.myspacecdn.com/i...ed42cb2183.jpg

the way i was trained to find problems like this is to look at the diagram and trace the problem to the last known source of power...and once you find your last point jump the relay, solenoid, switch ETC whatever it may be and replace or clean the connections.

thats the only insight i can share as i never had a problem like this on a vehicle. im used to having charging issues on the equipment i work on.

i have not fixed it yet...i am looking at everythign again...grounds seem ok and clean...dash is out again and no bad wires or anything, no metal/wire connections causing shorts, altenator is fine, battery fine, all wires at coil stuff tested fine, fusable links tested fine, checked all fuses...fine...i just cant figure the darn thing out!

also adding that now that i have changed the battery in my multimeter (it was reading voltage like crap cause of bad/dieing battery) the car runs around 11.85ish to 12.40ish volts...low end with lights on and high end with no load what-so-ever

your alternator should be putting out 14 volts

yea...i know

i actually forgot to re-read the first post

ripped the dash apart and now the car isnt charging...it could be a lot of things like a push pin on a wire harness is loose and slipped out...you could have corrosion because of the heater core that recently went out. lots of variables

i dont have schematics and i also hate looking at them but what you know and what you shared here is telling us you have a charging issue so stick with that circuit and start tracing wires with continuity checks (ohms check) and voltage checks....dont do guess work you will probably just make more problems.

trying to find out what the ECU would say what was wrong with the car, and it said there was no communication with vehicle?
any thoughts?

Bro it sounds to me like you have a short.

well...finished up the wiring for the new alternator conversion and still the same results...

Here is the wonderful story now.
I sold it, pratically giving up on the problem. The guy that bought it from me found out that a ribbon cable at the computer under the dash was fried. He replaced the cable solving the problem. He then sold it to someone i kind of knew. This guy that got the car then proceeded to take the car around a corner too fast, into a ditch, and into a pole. Now i am reunited with my car with a resto project on my hand with the front end all jacked up.
Now let the fun begin...(and the money fly away)

I have a picture of an engine light on my gages that stays on all the time. What does this mean?