MSD 6AL install on '77 911

[npresley]

I have a '77 911, that from factory had a Permatune CDI box with a 3 pin connector. The Permatune worked fine, but I apparently had to spend some money, so I decided to install an MSD box. I got an older MSD 6AL box (pn#6420) from ebay. I then got an MSD 2 Blaster coil, one of the vibration resistant ones, and a set of Clewett Engineering wires. I had previously installed a Pertronix unit to replace my points. Thanks to Timmy2 (fellow Pelican) I was able to get the thing wired and going. So, per the MSD install instructions and many bits of information for MSD box installs into a 911, I ran a wire to the battery connection on the starter solenoid. That's the big red wire from the MSD, and the big black wire I landed under one of the screws for the plate that holds on the electrical goodies in the engine compartment. I then wired the orange wire to positive on the coil and the black on the negative (both from MSD box), and removed the 2 wires from the factory harness. There are only two wires on the coil, both from the MSD box. I then terminated the thin red wire to the red in the 3 pin connector. The red is the middle terminal. Now pull back the rubber boot on the 3 pin connector; there is an index in the plastic housing. The white wire opposite the index gets the white wire from the MSD box. That's it. I hope others can use this information.

[cfassett]

I'm in the middle of this installation, myself. My car also had a PermaTune box, though it was non-functional. However, the wires on mine appear to have been messed with back in the 90's when this car last moved under it's own power.

You'll see in the photos, there are 2 plugs that were in the PermaTune. the red runs from one to the other. The white wires going into each plug were spliced together. The set on the larger plug has a black wire also spliced in, and this went into a separate inlet on the PermaTune. Confused? I am.

Do I have the small red from the MSD in the right connection? What about these splices? Should I eliminate them? And, one more question, just to confirm since the aluminum plate is mounted onto the body rubber mounts. This plate is what the MSD is grounded to?

[cfassett]

Or is this female the plug that the small red wire plugs into?

[juanbenae]

ive done this twice and suggest fusing the hot line from the starter as soon as it enter the motor compartment. it'd really be better closer to the starter, but having it visible in the motor compartment is a reminder if there are starting issues to trouble shoot. lots of hot power running through that line.


couple other things. the coaxial line from the distributor can get complicated and is easily switched and will cause havoc with the tach operation. in my 78 no tach adapter was needed when going to the MSD unit, but my 75 chassis with an early 3.oL transplant did require the tach adapter. you may want to consider adding the tach adapter in the initial wiring efforts because it's dam frustrating to get the thing completely wired up only to find the tach will not operate. lacing one in after the fact is a pain as you have to undo a bunch on the wiring you've just completed.

regarding the black wire from the MSD. I landed that on the ground stud just forward of the OE box location. I suppose since the aluminum mounting plate is secured to the body one of those studs would work, but the MSD box gives you plenty of wire slack to run it to the stud ive suggested. it also is a bit cleaner as you can gather it with the harness running toward the fire wall very tidy like.

[cfassett]

Thanks Juanbenae! Can you recommend a fuse size for the big red line?

What about these white lines that are spliced together. Are they supposed to be that way?

[juanbenae]

as best I can recall a 15 or 20 AMP. id go out and pull what's in there to confirm, but im in the last throws of a move and the car is 150 miles away at the new place already.

regarding the wires you ask about I have no clue. im wiring & electrical impaired and when doing my installs I went line by line with the instructions checking and rechecking the layout. both times I also thinned out and removed nearly all of the motor compartment remote fuse box stuff including the heater blower motor and rear defrost wiring. also removed all of the CIS & other wiring from the 14 pin connector that was no longer needed as I moved to carbs both times.


removing the items I alluded to it really simplified things because it cut the amount of wiring down to bare necessity making things easier to identify and kept me from becoming more confused than I was as it was. ive glanced at my notes here and see no mention of a white wire, although my notes mostly identified what was removed. does the white wire come from the large harness bundle from the fire wall? where does it terminate?

there are plenty of guys much smarter than me here that could likely be of more help. best of luck

[timmy2]

Two white coax wires are used in the ‘77 for points, tach and coil. (Same for 73.5 to ‘77)

Porsche CDI wiring: with 2 white coax wires:

One white coax wire runs from the 3 pin connector to the coil. Center white goes to positive, shield goes to negative. Shield also goes to the mounting base of the coil. (Soldered connection of brown wire to the coax shield wire near the coil)

The other white coax center wire comes from the points (shield attached to a ground terminal by the dizzy) to the small white T connector and then jumps over to the 3 pin CDI connector. (Points input to CDI and tach input to tach wire)

The shields of all 3 coax wires are soldered together near the 3 pin and T connectors (as in your photo) and they go to the CDI case ground via the soldered black wire.

The red from CDI connector to T connector runs switched power to the CDI.

The red on the body side in the female T connector in your photo is switched power for the CDI. The other wire in there runs directly to the tach. (Black/purple)

Install MSD:
Disconnect and tape off wires to CDI, coil and dizzy.

Thin red and “tach out” (grey?) to white T connector.
Run the 2 coil output wires to the coil.
Run points input wire to dizzy. (Points)
Run fused fat red to battery constant. (Most go to starter)
Run big black to a body ground.

Run and see if tach adapter is needed.

[cfassett]

Thank you all for the guidance! First there was no spark, then moved the ground from the aluminum plate to a bar attached to the engine, and then...

Ignition! First time since like 1994!

I need to locate that ground stud Juanbenae indicated, and bolt it there. Right now its grounded with a set of clamps.

[timmy2]

Ground stud is behind fuel filter/accumulator area.
Should be a strap from the CDI panel to it.

[cfassett]

Found the stud. Found a strap too, but it was only attached to the stud. Other end was loose.

It's supposed to be attached to the aluminum panel?

[timmy2]

Originally Posted by cfassett

Found the stud. Found a strap too, but it was only attached to the stud. Other end was loose.

It's supposed to be attached to the aluminum panel?

Yes, to the rubber mounting stud on the panel side. Makes contact with Aluminium.
You could double up the fat black to that stud at the panel with the strap if it is in good shape.
Or run to the body stud.

[cfassett]

That makes total sense. That's why an aluminum panel on rubber mounts would serve as a ground. But not mine, because the strap was off.

Thanks for taking the time to help.

[timmy2]

No problem with the help.
I like to help diy guys figure it out and then build harnesses for those that won’t or can’t diy.