Help, electrical something...

You were running on battery voltage and the load was dropping the voltage down to 9 volts.

Either the alternator died or the fuse link for the alternator burned up. The fuse link for
the alternator is a dark green wire up next to the starter solenoid.

Most auto parts stores will check the alternator for free on or off the car.
Diagram courtesy of Tmoss & Stang&2birds


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif




If the fuse link didn't go bad, the alternator did. It is time for a 3G conversion. The 3G is a 130 amp alternator commonly used
on 94 and later 5.0 Mustangs. Mine came off a 94-95 Mustang.

Here's websites with pictures of the 3G installation...

See http://www.geocities.com/smithmonte/Auto/3G_130A_Alternator_Upgrade.htm -
all the tech data you could ever want to know
OR
http://www.mustangcentral.net/tech/alternator.html - excellent pictures of installation

Use these sites for information on the right way to do the wiring. Some people will tell you
that you can skip the wiring upgrade, but it will catch up with you sooner or later. A fire in
the wiring harness is ugly and expensive.

Under no circumstances connect the two 10 gauge black/white wires to the 3G alternator.
If the fuse blows in the 4 gauge wire, the two 10 gauge wires will be overloaded to the point
of catching fire and burning up the wiring harness.

The secondary power ground is between the back of the intake manifold and the driver's
side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor
clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator
needs a 4 gauge ground wire running from the block to the chassis ground where the battery
pigtail ground connects.

Electric fan = 3G alternator if you want long life & reliability from your car.
The electric fan saves some HP. The stock fan's parasitic drag runs from 7-12 HP depending on
who you talk to. The electric fan uses about 1/2 HP of power from the electrical system.

Figure this:
Ignition system & computer = 12 amps
Fuel pump = 12 amps
Exterior lights = 15 amps
Fan (heater or A/C) = 15 amps (can run between 5-25 amps depending on setting)
Radio & instruments = 10 amps
Wipers = 10 amps

That's grand total of 74 amps from a 65 amp alternator. Talk about overdrawn at the bank!

See WWW.partsexpress.com for the fuse & fuse holder.
Fuse @ $3.90 each (need one) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=071-952

Fuseholder @ $5.80 each (need one) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=263-630

4 gauge black wire @ $1.25 a foot (use string to lay out routing & determine length) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=100-196

4 gauge red wire @ $1.25 a foot (use string to lay out routing & determine length) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=100-194

4 gauge ring crimp terminals (package of 5) $3.25. http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=095-584

3/4 “ Black heat shrink tubing, 4ft length, $3.56
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=082-058

3/4 “ Red heat shrink tubing, 4ft length, $3.56
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=082-064

Pre-fab 4 gauge cables with lugs already on the ends are available in most auto parts stores.
Look for the starter switch to starter cables.

I am very careful to maintain backwards compatibility, so I did things a little different. The
white/black stator wire gets the insulation stripped back about 1 1/2" in the middle of the
wire & cut in the middle of the stripped area. Then a short length of white wire with a 1/4"
slip on female spade connector gets spliced on to the white/black wire. Slide on enough
1/4" heat shrink tubing on the white wire to cover the solder splice you are going to make.
Next all 3 wires get soldered together & the heat shrink tubing gets shrunk. When you finish,
the white/black wire looks like a "Y" with 1 white arm and 1 white/black arm. I left the
black/orange wires connected to the original plug and did not do anything to them. When you
are done, the original plug still has all the wires connected to it and they are still functional.
The extra white pigtail wire that you spliced, soldered in & covered with heat shrink tubing
is just long enough to plug into the 3G without much left over.

I ran the 4 gauge wire under the front of the engine next to the 4 gauge wire for the starter power feed.
It came up the same
path as the fuel injector supply lines, and gets bolted to the power output lug of the 3G alternator.
The 125 amp fuse is mounted on a plastic panel bolted to the stock ignition coil mounts.
One of side of the fuse has a 4 gauge wire connected to the battery side of the starter solenoid &
the other to the 4 gauge power feed wire for the alternator.

I had some 1" silicone aircraft heat shield tubing that I fed the 4 gauge alternator power
feed wire through and tie wrapped & clamped it in place with some aircraft cushion clamps.
That provided the wire extra protection from road debris and rocks. Some heater hose
could be used to do the same thing.

I have an additional 4 gauge ground running from the power steering pump mount to the
common chassis ground being pointed to in the photo.

Apart from the grinding I did on the mount bracket, there wasn't much to it. Rather than
just grind a notch, I ground the whole web back to the thick part of the bracket. It looks much
more factory that way.

jdium said:

Wouldn't 20 miles of driving with the headlights on kill the battery, or atleast drop it enough to make the voltage gauge dip from 9?

I'll check the fuse link once I can see outside.

The rest of the post is a bit overkill for troubleshooting...

Click to expand...

The point of the rest of the post was to illustrate the fact that your present alternator isn't up to the job and provide an alternative.

Did you check the fusible link as previously suggested ?


When the alt went out, it may have taken out the link.

jdium said:

I did not check it. Is the selanoid seperate from the starter on these cars? I'm still new to this. Also, would this fuse being blown just hinder the voltage?

Click to expand...

yea the solenoid is on the drivers side. follow your ground cable from the battery and you will see it its kinda near the battery

looks like this

did you look at your dash volt gauge when the other car was hooked up? are the lights still dim? if you had a mutimeter you could check at the battery how many volts are there. with the car off with ignition on, running . it sounds like you should install a capacitor (sp?) after you fix the problem so this does not happen again.

Since you admit that you're new, be sure to go back and re-read Jrichker's post about converting to a 3G.

BTW, do you still feel his post was overkill? If not already known, he is the resident wiseman here.

I will say that stuff like this happens - the wiring in these cars sucks in general. You really might want a reliable DD if you do not have the inclination to spend a few mins doing diagnostics and a little more time for retrofts and repairs. I say that not to be a jerk but so you are not surprised by something acting up. We'd hate to hear that you rolled the car off a cliff because it was so aggravating (instead of being a source of enjoyment).

Good luck.

I definetely agree about the 3g alt. upgrade.. in my opinion that it is absolutely neccessary especially with your stereo and amp... and you can pick up a capacitor pretty cheap for your amp.. the capacitor stores enough power for when the loud bass kicks in... that can be too much load.. especially for a old alt to keep up with... just replacing your old alt.. is kinda a waste of money in my opinion.. why wouldn't you just have done the 3g alt. upgrade.. it is a really easy upgrade.. only big thing other than following the instructions is to upgrade the main power wire... you don't even need to take the old wires out.. you just cut off the ends and tape them up... then just run the new power wire ... 4gauge is smart.. to the solenoid.. if you ever get underdrive pulleys.. or a electric fan... the upgrade is a must especially with that 300w amp. If you are dead set on not bothering with the upgrade.. consider picking up a overdrive pulley... that could help a bit. 18.95 from summit racing.

jdium said:

Didn't look at the gauge with the jump car hooked up. The weird part is it is running great, lights seem a little below where they were normally, but not terribly so. It's like the alt just decided to half-ass it now...

Click to expand...

An alternator that does so-so until you create a decent accessory load has often dropped a diode. The alt gets by till a big load is created, where it shows that it cant keep up anymore.

If you can, keep your existing 2G around since it kinda works. You can use it for a spare if your new (3G ) needs repair work in the future (some of us order them from online sources, and thus have no alternator for a couple weeks if the new alt needs warranty repair).

Good luck.

I've posted once before but get a Aerostar van alt. The vans with all the rear a/c have stock 180amp, AND!!! they bolt right into a fox not mods needed, WORKS AWESOME! I have one in mine.

Matt