I just installed a new MSD ignition, 6AL ignition box, distributor, and coil on my 69 Roadrunner. I am have a hard time finding a constant 12V wire to power the ignition box. All wires I put a volt meter on either drops to 9V or less when cranking, or show 12V when cranking then voltage drop after I stop turning it over. I can hook a jumper from the battery to the 12V on the ignition box and the engine fires right up and stays running, but won't shut off when I turn the key off (I have to disconnect the jumper from the battery) which I understand. I am not using the ballast resistor as per the instruction from MSD. I rewired the whole car with a Painless wiring harness about 10 years ago and all has been working fine. Can anyone suggest a wire that stays constant 12V thru the ignition switch?
Looking for a switched constant 12V wire
- Thread starter Middy
- Start date
With the resister bypassed you should have 12 volts on the coil feed. Some people run a jumper at the switch. Being its painless you will have to read the instructions for the correct colors.
- Local time
- 11:13 PM
- Joined
- Oct 8, 2012
- Messages
- 6,301
- Reaction score
- 2,677
- Location
- Valencia, España
it doesn't actually exist a full 12 volts source from ign switch on stock config. Just jumping out, splicing or whatever method choosen to bypass the ballast will make it and getting the voltage from the wire arriving to + lead of coil or anywhere from same wire.
my fav... a modified ballast on back removing the resistor from the ceramic piece with a jumper wire into the groove to keep the stock look on firewall is the coolest. that will allow to get back to stock if needed/whished without deal with a hacked wiring and just replacing the ballast with a new one.
HOWEVER, using a "painless" wiring harness, will need to make the job inside the cab, splicing together brown ( Ign2 ) and blue ( Ign1 ) wires coming out from ign switch into the pink "painless" harness wire
my fav... a modified ballast on back removing the resistor from the ceramic piece with a jumper wire into the groove to keep the stock look on firewall is the coolest. that will allow to get back to stock if needed/whished without deal with a hacked wiring and just replacing the ballast with a new one.
HOWEVER, using a "painless" wiring harness, will need to make the job inside the cab, splicing together brown ( Ign2 ) and blue ( Ign1 ) wires coming out from ign switch into the pink "painless" harness wire
It's possible to see the battery voltage drop to 9V during cranking especially with the original gear reduction starter and a healthy engine.
For a MSD install I would use the 12 volt side of the ballast resistor for a trigger wire for a relay. You will get full power when the key is turned on with no strain on the original electrical system.
Are you trying to keep things looking stock or not? Here's a possible solution: add a relay in a line from the battery to the MSD. Control the relay with the ignition switch. Result: full 12v when key is on, dead when key is off.
- Local time
- 11:13 PM
- Joined
- Oct 8, 2012
- Messages
- 6,301
- Reaction score
- 2,677
- Location
- Valencia, España
about the relay option... I GUESS everything will depend on the relay sensivity for the voltage. Sometimes the ballast voltage can get as low as 4.5 or 5 volts. If the relay remains active with that, cool.
There is also a diode solution between ballast terminals, to keep the low voltage reading while in run for the coil going throught the ballast and still getting 12 volts on run circuit while cranking if using stock ignition system and need to add some 12 volts on any ign stage per any reason
anyway, since OP already mentioned is using the painless wiring, everything mentioned about the ballast bypass or mod is useless and he needs to splice together brown and blue wires coming out from ign switch to the pink wire of the painless harness
There is also a diode solution between ballast terminals, to keep the low voltage reading while in run for the coil going throught the ballast and still getting 12 volts on run circuit while cranking if using stock ignition system and need to add some 12 volts on any ign stage per any reason
anyway, since OP already mentioned is using the painless wiring, everything mentioned about the ballast bypass or mod is useless and he needs to splice together brown and blue wires coming out from ign switch to the pink wire of the painless harness
Well, how do race cars overcome the issue ??
I get the splicing Ign. 1 & Ign. 2 together but the pink wires in the painless wiring harness go to lights, dome lights, etc., so that's not right for what I have. Can I splice the two together and run a single wire to the MSD box? If so should I put a fuse inline of the single wire running to the MSD box?
Commonly a switched constant 12 volts to the coil. Cranking done buy a push button switch.
- Local time
- 11:13 PM
- Joined
- Oct 8, 2012
- Messages
- 6,301
- Reaction score
- 2,677
- Location
- Valencia, España
My bad... I was thinking on American Auto wire which gets a pink wire for the ign signal...
anyway, the wire running to the + lead of coil, whichever color would be is the one which needs both wires ( blue and brown ) being spliced as soon leaves the ign switch if the dash harness you got includes fuseblock and everything to replace the stock wiring.
here is the diagram section ( for ign and charging ) I made for a member here with a 64 Fury and using an American Auto wire kit with an HEI dist with divorced coil ( similar to the MSD setup )... painless could be something similar just diff colors.
for full view, click the link
https://i.postimg.cc/50HhWz2h/Ignition-and-Charging-circuit.jpg
anyway, the wire running to the + lead of coil, whichever color would be is the one which needs both wires ( blue and brown ) being spliced as soon leaves the ign switch if the dash harness you got includes fuseblock and everything to replace the stock wiring.
here is the diagram section ( for ign and charging ) I made for a member here with a 64 Fury and using an American Auto wire kit with an HEI dist with divorced coil ( similar to the MSD setup )... painless could be something similar just diff colors.
for full view, click the link
https://i.postimg.cc/50HhWz2h/Ignition-and-Charging-circuit.jpg
Last edited:
Thanks for the diagram! I won't be able to try this until Tues., or Wed., but I can't wait!
- Local time
- 11:13 PM
- Joined
- Oct 8, 2012
- Messages
- 6,301
- Reaction score
- 2,677
- Location
- Valencia, España
well in your case, the wire running to the coil on diagram won't be running to the coil, but to the MSD ign wire. Coil on the MSD system using the MSD ign box gets its signal straight from the box on its own wires
Yes, that is correct, just needed the idea to splice Ign. 1 & Ign. 2 together! Thanks for the info.
Similar threads
