Alternator overcharging

[87 T-top]

I have an alternator that is putting out about 50 volts. I left the key on one afternoon and killed the battery. When I tried to "jump" the car one of the wires coming to the starter relay "smoked" literally. The two wires from the alternator joined and then went to the relay, I replaced them with two wires to the relay. One of the wires I replaced has fuse inline and it has blown the 15 and 20 amp fuses and shows output of 50v. I have replaced both wiring plugs that go to the alternator, checked the wiring for continuance and grounding , checked the new alternator and it checks good, added a engine to body ground to make sure it was grounded.
Any more ideas? Do the two wires that joined, need to be together and then go the relay or would that make any difference?
Any ideas or help would be appreciated

 

[jrichker]

Diagrams courtesy of Tmoss & Stang&2birds

Notice the yellow/white wire with the fuse link. It is the voltage regulator sense wire. If it open circuits or shorts to ground, your voltage regulator will not work correctly. That means you could get a very high or very low output voltage.

Caution!!! Disconnect the negative cable from the post on the battery before making any resistance checks. Failure to do so could damage the meter or give incorrect results of any resistance measurements.

Use the Ohms function on your meter to check it out. It should show less than 1.5 ohms from the green fuse link on the starter solenoid to the yellow/white wire on the voltage regulator D shaped plug.





See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 86-95 5.0 Mustang wiring Mustang FAQ - Engine Information 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 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 94-95 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_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

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

 

[87 T-top]

OK, A buddy of mine checked the voltage regulator sense wire and it checked out good. But he did ask about another voltage. The light green/red wire from the ignition switch through "Batt" light to the voltage regulator has 12v with the regulator plug unplugged but only 2.3v with it plugged in.

 

[87 T-top]

I took some voltage measurements tonight
I circuit Key ON, wiring unplugged from Alternator 12V
I circuit Key ON, wiring plugged in 2.9V
A circuit 12V

With Car running,
B circuit 50V
S circuit 25V

 

[HISSIN50]

Your first portion looks fine.

"With car running" looks like crap. Have the alternator tested and DO NOT start the car with that alternator in place in its present condition. You take a chance on blowing up your battery, starting a fire, and frying the electronics on the car.

 

[87 T-top]

I installed a known good alternator last night and it was overcharging as well, there wasn't enough difference in voltage to call it different.

The problem came after I had left the switch on, so I pulled the wiring harness connector from the ignition switch and around the "Batt" terminals there was noticible heat damage. The connector showed signs of "melting" around the Batt terminals. I checked for continuity to ground on this connector and I had continuity on the following terminals/wires:

two yellow wires that run to the battery
gray/yellow wires that runs to the fuse panel
red/green and brown/pink that run from the switch through alternator warning indicator to the I circuit in the regulator

Should these wires show continuity to ground?
I am running out ideas in the alternator circuit.

 

[HISSIN50]

If those wires showed continuity to ground, you'd be blowing fuses and links.
If you really have 50V running through the car, I'm surprised you haven't had a fire and/or fried half the electronics on your car. You would probably not have a functional light bulb left, for instance.

 

[87 T-top]

I have a fuse holder inline from Alt to starter relay, that is probably the only reason that the car hasn't burnt to the ground. When checking from the "hot" side of the fuse holder to ground I get 50V.
When I tried to jump start the car several weeks ago it was well on its way to burning if I hadn't immediately taken the jumper cables off.

 

[87 T-top]

alternator overcharging update

After not being able to find the problem in the wiring or the parts, I replaced the wiring harness for the alternator, headlamps, park lights, turn signals, and fog lights. The charging system is putting out 14.65V.
My question is: The wiring harness came from a 90GT, is there any difference in this wiring harness? The connector for the radiator overflow bottle is different, is this the only difference or are there a few others as well

Thanks