I am hooking up a MSD 6AL and the small red wire that is to go to switched 12v, most people hook to the brown positive wire at the coil.

That brown wire runs to the ballast resistor.

Could I hook onto the ballast? Does it matter what side?

With MSD you bypass the ballast so the small red wire gets fire in "crank" and in "start" which means the coil will get full voltage. this is good if you are using a MSD compatible coil designed for this. this is as far as my MSD knowledge goes and with the fast rise time of the MSD system a regular coil not designed for full 12V may or may not be OK with full voltage/no ballast & not sure if the small red wire needs full 12V which if so means you could not power it thru the ballast. here's a BTT for ya & wait for someone who knows MSD to chime in

Do NOT wire it like that. If you don't have the paperwork, you can download it from MSD. The ONLY wires that go to the coil are from the MSD box. You eliminate the ballast resistor altogether. That small red wire, as Robert stated, is to be hot during crank and run. If you don't wire it exactly as MSD says, you will let the smoke out

I just installed an MSD, and connected both the run and start leads to the small red wire so it would fire during cranking and run. Works fine. I looked at the instructions, and basically they want you to hook to a 12+ switched wire, so it turns on and shuts off the ignition system. I assume all there is is an internal relay which then supplys the juice to the ignition components. If you can find a switched 12+ that is still hot during cranking, fine. Call MSD tech and ask about using both start and run wires, just to make sure. I was willing to chance it, but don't want to advise you to unless they give the green light. I don't see a problem, but you just never know.

Discussed much through the years.....definitive answer is you don't HAVE to use the ballast with an MSD6A, but you CAN if you want to. All that signal is providing is effectively a logic level - 6V, 12V, it doesn't care, the coil supply is not routed from there.

Those who leave out the ballast do so because it is one less failure point, they don't have a ballast, or just don't want it there.
Those who leave it in do so because it is an easy source of a start/run signal, and/or they want to leave the ballast in so they can revert to a stock system easily if required (eg if the MSD fails)

Choose your preference, but the MSD does not care.
(yes, this is verified by MSD themselves)

It's true that the MSD signal voltage isn't important but how can you run the ballast and still have a signal signal in both Start and Run?

"and connected both the run and start leads to the small red wire so it would fire during cranking and run"

Gotta do that or you'll spin your wheels wondering why the car starts when cranking but dies as soon as it fires up and you let go of the key. Been there... Connect the run and start together any where convenient. I do it on the back of the ignition switch and then run only one wire out the firewall connector.

Thats right as you dont need the ballast with MSD so you just take it out. You do need a 12 volt key on (ign 1) and the 12 volts while cranking (ign 2). If you dont hook the ign 2 circuit up it wont start while cranking until you let go of the key. And since ign 1 and ign 2 are seperate circuits on the ign switch you wont have any backfeed from the ign 1 the 12 volts at key on so it wont crank when the key is turned to the run posistion. Ron

I joined the blue and brown wires out of the bulkhead and took to the MSD. Easy peasy

By using the factory wiring - it supplies voltage to the coil during crank AND run, if you use that as your input to the MSD (small red) that's all you need. IMO, another advantage of keeping ballast - no recreating a supply that the factory already has...

As covered just connect the two circuits at the ign sw or bulkhead or bypass ballast or hide wire in or behind ballast. The other unaswered Q (to me) is can you run a "regular" (non MSD type) coil with full voltage (bypassed) ballast in ign1 (run) & I ain't talking about an E coil (which iirc you can with that type) but a regular coil like if you were doing a conversion. So if you convert to MSD do you need a MSD coil or an E coil to avoid burning the coil out?

"So if you convert to MSD do you need a MSD coil or an E coil to avoid burning the coil out?"

Depends on the coil resistance. Most of the breakerless ignitions call for a specific coil resistance or narrow range of resistances to work with their box. Too high a resistance coil and the spark looses energy (not enough current through the primary side of the coil to charge it fully), too low a resistance coil and the coil can fry or the output transistors in the ign box can fry due to too much current. The current that used to run through the points to charge the coil is now unimpeded through the output transistors and goes directly to the coil with no ballast. The "start" and "run" wires were to bypass the ballast resistor when starting the engine for a hotter spark and then run through the ballast to limit coil current in the "run" mode.

Alright, got it, thank you!