• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech

90 mustang GT voltage/wiring troubles?

  • Thread starter Thread starter Deleted member 143610
  • Start date Start date Nov 4, 2008
D

Deleted member 143610

Nov 4, 2008
#1
  • Nov 4, 2008
  • #1
So here we go...
I have tired myself for weeks trying to figure out the problem. First, let me start off by saying that I just recently tore my whole dash apart and did all that happy stuff evolving a new a/c 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 pigtails coming off the alternator thinking corrosion was the cause of the bad voltage, and still, the same results.
i replaced both battery cables and checked the one from the starter to the relay...all good and yes...it helped....to a point...
the car sits around 13.5ish if not a little higher/lower.....starts, and dips like it should when it cranks...
when its running though, it creeps up reeeeally slow, and once it gets back to about 13.4-13.6ish voltage, that is where it sits.
granted i know that voltage is OK...but i dont like it bein OK. I would like to fix the charging problem so i know it is reliable. and if the car sits for a couple days it completely dies...

tested the new altenator and it is fine as well (brand new battery too)

I am running out of ideas...and help would be greatly appreciated!!

ps...nothing really electrical done to it except a MSD coil, autometer tach, and a head unit (no real system, just basic speakers to replace the stock ones and a new deck)
 

HISSIN50

"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
31,179
34
129
Nov 4, 2008
#2
  • Nov 4, 2008
  • #2
If all of your voltage drop tests looked ok, this might be about normal for a 2G (we dont know what idle RPM you see or if you had any load on the system).

A 3G retrofit would have been a nice alternative (next time perhaps).

For the battery crapping out after non-use, do a parasitic draw test on the system.
Good luck.
 

hotcobra03

Active Member
Nov 29, 1999
969
4
39
poteet,tx
Nov 5, 2008
#3
  • Nov 5, 2008
  • #3
My 03 cobra has read 12.8 to 13.4 since new .as to no start when car sits,i can go 3days and what ive heard from other posts its normal
 
D

Deleted member 143610

Nov 5, 2008
#4
  • Nov 5, 2008
  • #4
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
 
D

Deleted member 143610

Nov 5, 2008
#5
  • Nov 5, 2008
  • #5
HISSIN50 said:
If all of your voltage drop tests looked ok, this might be about normal for a 2G (we dont know what idle RPM you see or if you had any load on the system).

A 3G retrofit would have been a nice alternative (next time perhaps).

For the battery crapping out after non-use, do a parasitic draw test on the system.
Good luck.
Click to expand...

as of now....no load except the car engine itself...everything else is either off or pulled out (radio)

how would i go about doin that test? thus far i have found nothing visually or testing the links and crap under the hood

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

HISSIN50

"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
31,179
34
129
Nov 5, 2008
#6
  • Nov 5, 2008
  • #6
hotcobra03 said:
My 03 cobra has read 12.8 to 13.4 since new .as to no start when car sits,i can go 3days and what ive heard from other posts its normal
Click to expand...
That's not normal.


butkusjr said:
as of now....no load except the car engine itself...everything else is either off or pulled out (radio)

how would i go about doin that test? thus far i have found nothing visually or testing the links and crap under the hood

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

You need to use a DMM in series with the battery. Have every item in the car turned off and be cognizant of overloading the current rating on your meter. This link might help.

Good luck.
 
D

Deleted member 143610

Nov 8, 2008
#7
  • Nov 8, 2008
  • #7
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/images02/2/l_368050904da749d39dc7e3ec66c5f3f1.jpg

http://c3.ac-images.myspacecdn.com/images02/27/l_05638808325943858f550ea0a0914df6.jpg

http://c3.ac-images.myspacecdn.com/images02/25/l_a1bd8c4220bc4e049f5f45a7844af942.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/images02/36/l_1800b936ea1e45eba25120ba67e4ce98

http://c2.ac-images.myspacecdn.com/images02/61/l_0478155a22804f3b8fe2b4dbf5e1ac71.jpg

http://c2.ac-images.myspacecdn.com/images02/12/l_0bc7d68a903c4d88b77fe583bc3fd471.jpg

http://c4.ac-images.myspacecdn.com/images02/38/l_d0d4032bd6d34c3c825f18ed42cb2183.jpg
 

hotcobra03

Active Member
Nov 29, 1999
969
4
39
poteet,tx
Nov 9, 2008
#8
  • Nov 9, 2008
  • #8
Is it hooked to a relay.circuit 175 bk/y d fan relay?
 
D

Deleted member 143610

Nov 9, 2008
#9
  • Nov 9, 2008
  • #9
i have no idea...they were just sittin there under the dash...along with a few others that i couldnt find matches for...
 

Saleen0679

10 Year Member
Apr 14, 2005
876
24
49
Yakima, WA
Nov 9, 2008
#10
  • Nov 9, 2008
  • #10
You sure that's not Black with a Yellow tracer? Looks like it could be one of the leftovers for the convertible top circuit breaker. It kind of just hangs there above the steering column.

Behind the radio is usually the premium sound amp.
 
D

Deleted member 143610

Nov 9, 2008
#11
  • Nov 9, 2008
  • #11
it could be yellow too....it was jsut a ****ty looking wire color so i was taking a crack at it...it does look more yellow too
 
D

Deleted member 143610

Nov 20, 2008
#12
  • Nov 20, 2008
  • #12
HISSIN50 said:
That's not normal.




You need to use a DMM in series with the battery. Have every item in the car turned off and be cognizant of overloading the current rating on your meter. This link might help.

Good luck.
Click to expand...

weeeeellllll....it passed...yea
 

90topdown

Member
Feb 16, 2006
138
1
16
Philadelphia, PA
Nov 21, 2008
#13
  • Nov 21, 2008
  • #13
I just went through a little wiring/voltage drop nightmare on my 90. It may not be your problm but mine turned out to be a ground problem. Make sure that all 4 ground wires are there and the connections are clean

- engine block to firewall
- motor mount to frame
- battery to engine block, radiator support and dash harness ground point.
- dash harness ground point to frame

If you do a search, J Richker has a good write-up on it. Good grounding is essential with our cars. They are very sensitive to it.
 
D

Deleted member 143610

Nov 21, 2008
#14
  • Nov 21, 2008
  • #14
90topdown said:
- engine block to firewall
- motor mount to frame
- battery to engine block, radiator support and dash harness ground point.
- dash harness ground point to frame
Click to expand...

i know for sure where the battery to engine

the other ones i am kindof up in the air on...
 
D

Deleted member 143610

Nov 24, 2008
#15
  • Nov 24, 2008
  • #15
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
 
D

Deleted member 143610

Nov 26, 2008
#16
  • Nov 26, 2008
  • #16
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?
 

Mr. Rustypwnz

Advanced Member
Jun 1, 2005
1,761
63
69
indianapolis/ valdosta ga
Nov 27, 2008
#17
  • Nov 27, 2008
  • #17
butkusjr said:
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?
Click to expand...

what did the ecu drink last night? Has it smoked weed lately? your computer just might be asleep?
 

HISSIN50

"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
31,179
34
129
Nov 27, 2008
#18
  • Nov 27, 2008
  • #18
butkusjr said:
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?
Click to expand...

What scanner or reader were you using?

Use the test light or paperclip method to help rule out an issue with an additional device.
 
D

Deleted member 143610

Dec 5, 2008
#19
  • Dec 5, 2008
  • #19
well...finished up the wiring for the new alternator conversion and still the same results...
 
D

Deleted member 143610

Aug 27, 2009
#20
  • Aug 27, 2009
  • #20
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)
 
You must log in or register to reply here.

Similar threads

Alternator not charging
  • SchwarzStock
  • Jul 6, 2026
  • 1965 - 1973 Classic Mustangs -General/Talk-
Replies
2
Views
84
1965 - 1973 Classic Mustangs -General/Talk- Jul 19, 2026
SchwarzStock
E
2007 GT Stalls when lights or a/c turned on
  • ejscarfo
  • Jun 22, 2026
  • 2005 - 2009 Specific Tech
Replies
2
Views
138
2005 - 2009 Specific Tech Jun 29, 2026
ejscarfo
E
C
Electrical HELP! 1989 5.0 Stick, Voltage Bleed onto Ignition Trigger wire
  • ChickenDeluxe
  • May 14, 2026
  • Fox 5.0 Mustang Tech
Replies
7
Views
239
Fox 5.0 Mustang Tech May 24, 2026
ChickenDeluxe
C
Electrical Ron Francis Headlight / Alternator Harness
  • dan50
  • Apr 30, 2026
  • Fox 5.0 Mustang Tech
Replies
0
Views
228
Fox 5.0 Mustang Tech Apr 30, 2026
dan50
C
Stock 1993 charging issue at idle
  • Charlie1
  • Sep 21, 2025
  • Fox 5.0 Mustang Tech
Replies
7
Views
335
Fox 5.0 Mustang Tech Sep 24, 2025
Mustang5L5
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?