HELP!!! WIRING ALTERNATOR MASTER DISCONNECT SWITCH

For a battery cut off switch, see http://www.moroso.com/catalog/categorydisplay.asp?catcode=42225
is the switch http://www.moroso.com/catalog/images/74102_inst.pdf is the installation instructions.
Use the super duty switch and the following tech note to wire it and you will
be good to go.

Use the Moroso plan for the alternator wiring and you risk a fire. The 10
gauge wire they recommend is even less adequate that the stock Mustang
wiring.

There is a solution, but it will require about 40' of 18 gauge green wire.

Wire the battery to the two 1/4" posts as shown in the diagram.

The alternator requires a different approach. On the small alternator plug
there is a green wire. It is the sense lead that turns the regulator on when
the ignition switch is in the run position: look for a wire marked 904 on the
lower RH side of the attached diagram. Cut the green wire and solder the
40' of green wire between the two pieces. Use some heat shrink to cover the
splices. See http://fordfuelinjection.com/?p=7 for some excellent
help on soldering & using heat shrink tubing.

Run the green wire back to the Moroso switch and cut off the excess wire.
Try to run the green wire inside the car and protect it from getting cut or
chaffed. Crimp a 18 gauge ring terminal (red is 18 gauge color code for the crimp
on terminals) on each wire. Bolt one ring terminal to each of the 3/16" studs.
Do not add the jumper between the 1/4" stud and the 3/16" stud as shown it the
Moroso diagram.

How it works:
The green wire is the ignition on sense feed to the regulator. It supplies power
to the regulator when the ignition switch is in the run position. Turn the
Moroso switch to off, and the sense voltage goes away, the voltage
regulator shuts off and the alternator quits making power.

See the following website for some help from Tmoss (diagram designer) &
Stang&2Birds (website host) for help on 88-90 wiring and lots more…

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

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

Diagram courtesy of Tmoss and Stang&2birds.




Rear mounted battery ground wiring. Follow this plan and you will have zero
ground problems.

One 1 gauge or 1/0 gauge wire from battery negative post to a clean shiny spot
on the chassis near the battery. Use a 5/16” bolt and bolt it down to make the
rear ground. Use a 1 gauge or 1/0 gauge wire from the rear ground bolt to a clean
shiny spot on the block.

One 4 gauge wire from the block where you connected the battery ground wire to
the chassis ground where the battery was mounted up front. Use a 5/16” bolt
and bolt down the 4 gauge engine to chassis ground, make sure that it the metal
around the bolt is clean & shiny. This is the alternator power ground.

The computer has a dedicated power ground wire with a cylindrical quick connect
(about 2 ½”long by 1” diameter. It comes out of the wiring harness near the
ignition coil & starter solenoid (or relay). Be sure to bolt it to the chassis ground
in the same place as you bolted the alternator power ground. This is an
absolute don’t overlook it item for EFI cars

Picture courtesy timewarped1972

Crimp or even better, solder the lugs on the all the wire. The local auto stereo
shop will have them if the auto parts store doesn't. Use some heat shrink tubing
to cover the lugs and make things look nice.

I used the above method to wire my cut-off switch and it worked great!

jason89gt said:

OKAY SO WHAT YOUR SAYING IS I CAN'T USE MY MOROSO SWITCH #74101! I WOULD HAVE TO GET THE MOROSO SWITCH 74102 WITH THE 2 EXTRA TERMINALS. CUT THE GREEN WIRE ON THE ALT AND THE WIRE THAT GOES INTO THE ALT GOES BACK TO THE SWITCH. THE OTHER HALF OF THE GREEN WIRE THAT IS THE HARNESS ALSO GOES BACK TO THE OTHER SIDE OF THE SWITCH. AM I CORRECT ON THIS? DOES IT MATTER WHAT SIDE OF THE SWITCH THE GREEN WIRES GO TO? THE ONE FROM THE ALT AND THE ONE FROM THE HARNESS. SO THE WIRES ARE MAKING A BIG LOOP THROUGH THE MASTER SWITCH. HOPEFULLY THIS IS CORRECT PLEASE EMAIL THANKS JASON

Click to expand...

You are correct. Easy to do and works good.

jason89gt said:

SO IT DOESN'T MATTER WHICH GREEN WIRE GOES TO WHERE ON THE DISSCONECT SWITCH. ONE GREEN WIRE ONE SIDE OTHER GREEN WIRE OTHER SIDE. CORRECT? THANKS JASON

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Correct, it doesnt matter.

Voltage spike? From what? Your cutting power, thats it. Mine works awesome, shuts the engine right down. Just make sure you dont follow the Moroso switch directions and put the little jumper wire from the big terminal on the switch to the little terminal on the switch. If you follow jrichker's method to the "T" you'll be all set.

And by the way, theres not power to those small terminals, they're simply an "open" and "closed" circuit.

I hate to hijack this thread but I have a similar problem. My master disconnect switch only has the two big terminals on it. Where does the alternator get wired to? I asked before and someone suggested the constant power side but when I try to crank the car the fuse pops. What could be the problem here? Thanks

NJCstang said:

I hate to hijack this thread but I have a similar problem. My master disconnect switch only has the two big terminals on it. Where does the alternator get wired to? I asked before and someone suggested the constant power side but when I try to crank the car the fuse pops. What could be the problem here? Thanks

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Read the ENTIRE post - everything you need is in here.