MSD ignition power shortage?

[Calgary351GT]

Has anyone ever ran short on power for their MSD ignition (6AL) to the point where their car sputters on the track at high rpms?

First of all. I've upgraded to a 3G alt. on my 351W, 90 GT. (carbed). I've checked the output of the alt. and it is fine until I turn everything on (fan,lights,stereo and elect fan), then the output drops to about 12.5 volts.

I had a situation once where I had ran the stereo for awhile with the car off. It started fine, but when I gunned it the tach jumped to like 7000 rpm and the rev limiter kicked in and out with the car really only reving at about 3000rpm.

Once the battery charged a bit it settled down.

Last night, at the track, as I was staging I could see the tach jumping around like it did before every time I touched the brake. As well, I was gettting some sputtering at 6000 rpm. (not usually a problem-I shift at 6500).

I think it's the ignition. Also, not sure if this is related but the ignition was hotter than hell after a few passes. And no, its mounted on the fender, nowhere near anything hot. In fact, it's mounted right under the original air intake so it gets cool air blown over it.

 

[jrichker]

Do you have a 4 gauge power wire and an additional 4 gauge ground wire for the 3G installation? There is no reason for the voltage to drop off to 12.5 volts with a 3G alternator and normal load.

 

[Calgary351GT]

I used the stock harness that came with the 3G alt.

 

[jrichker]

Here's how a 3G alternator should be wired into an 86-93 Mustang.

Old alternator power plug

Rear view of 3G alternator

Starter solenoid wiring 86-91 5.0 Mustangs with standard starter

Starter solenoid wiring 92-93 Model cars and earlier models with high torque mini starter.

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 & alternator

Picture courtesy timewarped1972

 

[Calgary351GT]

Well I'm just using the stock ground strap from the block to the chassis.

I also talked to an MSD tech. He told me to make sure I didn't having any power wires or spark plug wires running near the ones between the ignition and the distributor....And funny enough, my coil wire is RIGHT there. That might be bad

I also heard a bad battery might be the problem. Mine is one from Costco that came with the car when I bought it!