3g alt ground


May 18, 2010
Cleveland, OH
i put my 3g alt in and it is not charging the batter. had alt tested and it is good. i am assuming it is because i have not grounded it yet. i have gathered from jricters posts on this subject that the groun goes from the back of the intake manifold to the screw in between the washer fluid fill tank and battery.

well i have two wires there now, one goes to the computer and the other is just dangling there. so if i run a 4 guage wire from this point were does this connect to the intake manifold? and is there anywhere else i can conncet it?

would the lack of this ground cause my alt not to charge the battery?

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SN Certified Technician
Mar 10, 2000
Dublin GA
See http://www.stangnet.com/mustang-forums/646825-3g-alternator-install-how.html#post6673702 for correct 3G installation instructions

2.) 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 or high output current alternator needs
a 4 gauge ground wire running from the block to the chassis
ground where the battery pigtail ground connects.

The 3G has a 130 amp capacity, so you wire the power side
with 4 gauge wire. It stands to reason that the ground side
handles just a much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery & extra 3G
alternator ground wire as described above in paragraph 2. A screwdriver
points to the bolt that is the common ground point.
The battery common ground is a 10 gauge pigtail with the computer ground
attached to it.

Picture courtesy timewarped1972

Correct negative battery ground cable.

3.) The computer has its own dedicated power ground that comes off the ground pigtail
on the battery ground wire. Due to it's proximity to the battery, it may become
corroded by acid fumes from the battery.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness.


May 18, 2010
Cleveland, OH
thanks, sorry for such obvious questions but would i just attach the new 4 guage ground wire to any bolt on the back ot the intake manifold?

also, is this why my alternator is not charging the battery?

thanks again


"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
The alt should charge without the additional power-ground.

Is the alternator powdercoated or painted? If so, that can interfere with the grounding plane (through the alternator mounting points).