MSD Installation questions

Ok guys, here's the poop: I scored an MSD-5 inigiton system on eBay the other day for about half what the MSD-6A units are going for. Basically, it is the same unit except it is designed for use at 5000 RPM and under. (No problem there with a flathead! ) Well, I commenced to reading the installation instructions that came with it and they say in no uncertain terms to use a coil WITHOUT an internal ballast resistor, even though the MSD unit needs a 12-volt supply to make it work. The Pertronix setup I have in ther now also needs 12 volts at the input power supply.

What am I missing here guys? Why is that ballast resistor so derned important, and how do I get around it?

 

Ballast resistors are/were used to extend the life of the points and condensor from what I've read I seem to recall.

Get around it? Take it out, buy a Pertronix Flame Thrower, or a MSD coil with no resistor or go to NAPA and ask for one with no internal resistor.

 

Yeah, that's what I thought also. The thing that threw me is the MSD instructions that state that you MUST have a ballast resistor in the circuit.

I did manage to find a wiring diagram on the Pertronix website, and it shows how they recommend wiring up the MSD unit with the Ignitor pickup. There's no ballast resistor in their diagram. I think I'm gonna call MSD and see if I can get anything out of their tech support guys.

 

I'm confused. The MSD says to use a ballast resistor or no? Wouldn't it be AFTER the MSD before the points/condensor (in your case the Pertronix) since the MSD needs a full 12 V to operate, hence saying to use a coil with no resistor, then the MSD, coil, resistor, distributor. With the Pertronix remove the resistor from the phrase.

Seems like the Pertronix knows what's going on.

 

The MSD still needs a coil to operate Tim.

 

That's where I'm confused. They tell you in the MSD instructions that if you have a coil with an internal resistor, to replace it with a coil that does NOT. (Of course they recommend their MSD Blaster coil) The diagram then proceeds to show you tapping the (+) side of the ignition circuit BEFORE the inline ballast resistor, so you have 12v going to the MSD unit. I know for a fact that the Pertronix will not run correctly on 8-9v, so I'm thinking that I don't need to change my coil OR my wiring at all, and just put the MSD unit in as-is.

In reading the MSD installation instructions, it seems like this unit was marketed toward older vehicles in the pre-HEI era. If so, then I can see where the ballast resistor would be necessary for a point-type setup to keep from frying the points.

 

Sounds like if you have the Pertronix installed allready, drop in the MSD and go.

 

Did I have my coil and MSD reversed? I shoulda looked at the PDF. Tried to type from memory on a HEI vehicle.

 

Pertronix tech support was much, much more helpful than the MSD folks. After they got over the idea of putting an MSD unit on a 58-year-old flathead in a JEEP of all things, they told me to wire it up just like the .pdf on their site says and it will run just fine. Gonna order up a Blaster coil too, just for S & G.

Thanks guys!