12stepvette

The wiring instructions for the MSD 6A say to use 12 volts from the ignition switch....will the existing positive resistor wire work?...or do I need to run a new wire ?

Garrett1972

run new wire, box needs 12 volts to run correctly, with resistor wire you might get 8 to 9. It might run, but not correctly.

lostpatrolman

The 12 volts from the ignition switch is just a trigger to turn the msd on and off. The thick red wire usually goes to the battery but ours it too far, so go to the starter. It should always get power. The thick black wire is ground, go to the engine or frame. If you are running an electronic distrib, the small white wire does not get hooked up. If it is ground out, the system will not start. The 12 volts from the ignition switch is just a trigger to turn it on and off. If you are using electronic distrib, then a good place to take the 12 volt switched is from the old positive wire that used to go to the coil. The coil does not use the old wires in electronic applications, it only uses the wires that come off of the msd box.

12stepvette

Thanks for the replies, I`ll run a new wire to the 12 volt trigger and terminate the resistor wire and tape it up to the engine wire harness....

71coupe

I used the factory resistor wire in my 71 with no problems via MSD's instructions. You have to remember that the resistor wire is now just a signal wire that sends and open/close.
Download the most current instructions from MSD and follow them exactly & you will avoid problems.
:cheers:

12stepvette

It`s confusing when you get conflicting information :crazy: :crazy:

lostpatrolman

71 coupe is right. There are 6 wires on teh MSD. 1 white which doesnt get hooked up. One big black, ground that to body or engine. One big red, constant hot, go to starter peg. Thin red wire, switched 12v, only used to turn msd on and off, similar to a relay. You can splice that small red wire into anything that turns on and off by the ignition. A good source for that is the old positive wire that used to hook up the the coil. Then there are 2 wires in a separate bundle that go to the coil. These 2 should be the only ones hooked up to the coil. Im not sure what wire you are refering to as resistor wire, i am guessing you mean the hot lead to the coil.


[Modified by lostpatrolman, 11:24 PM 5/5/2004]

i885744

where do you guys have your msd boxes mounted? I'm trying to fit one in my engine compartment, looks like i might end up building my own bracket to hold it somewhere near the passenger hood latch on my 73. Does anyone have any pictures?

12stepvette

I guess I didnt make myself clear enough, I`m running a stock tach drive distributor with a pertronix unit...I dont have a problem at all with the wiring on the box...the only wire hookup I am questioning is the small red wire that hooks up to the 12 volt ignition switch. I have 2 options there....use the original lead from the positive side of the coil which is a "resistor" wire....or run a new one from the fuse box which is not a resistor type wire.
I understand its just a "turn on" signal to the box, but concerned that the resistor wire only puts out about 9 volts.

I mounted my box on the drivers side firewall under the fender....had to remove the wiper fluid container to drill the holes...its away from direct engine heat and really cant be seen with the master cylinder and wiper fluid container hiding it.

thanks for all you help!!! :cheers: