I can't seem to find a 12Volt switched power lead to hook up my MSD inginition wire. All the leads either cut off voltage while cranking or drop to 8 volts. Is there a resistor or bypass that is reducing the power? I guess I will have to run a wire to the battery and put a on/off toggle in the dash. Any ideas?
12volt switched power?
- Thread starter doogie67
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Hack
15 Year Member
On my '70 there is a pink resistor wire in the key on voltage source wiring. When I wired up my Duraspark ignition I tapped into the pink wire right at the ignition switch. Right at the switch it's 12V.
I would say take the column cover off and probe at the ignition switch for 12V. You should find a switched source there.
edit: don't forget to put a fuse in the line and a grommet to protect the wire at the firewall! I'd hate to see you burn down your car.
second edit: D. Hearne was too fast! Beat me!
I would say take the column cover off and probe at the ignition switch for 12V. You should find a switched source there.
edit: don't forget to put a fuse in the line and a grommet to protect the wire at the firewall! I'd hate to see you burn down your car.
second edit: D. Hearne was too fast! Beat me!
65fastbackresto
Active Member
I kinda like the toggle switch idea
Could add a degree of antitheft to your car rather easily. Even if you goofed and left the keys in it, they`d have to know the switch was there to start it.
Could add a degree of antitheft to your car rather easily. Even if you goofed and left the keys in it, they`d have to know the switch was there to start it.
Rusty67
Dirt-Old 20+Year Member
The coil should have a resistor wire in it somewhere that limits its voltage at certain times. Thats the resistor for those external resistor coils like we have...
Not to mention, if it was 12 volts keyed then when you draw more juice you might starve teh coil... I've done that before, wired in a new device and then couldn't figure out why the darn thing wouldn't start anymore!
Not to mention, if it was 12 volts keyed then when you draw more juice you might starve teh coil... I've done that before, wired in a new device and then couldn't figure out why the darn thing wouldn't start anymore!
BullittStangV8
Founding Member
MSD's instructions is to wire the "red wire" on the ignition box to the old + coil wire. (I assume this means switched 12v) Am I right now in that what you guys are saying that the old + coil is not 12v switched in this case? As of right now, and I have not started the car, I have the red msd ignition wired to the old + coil wire.
http://www.msdignition.com/pdf/6 series/6series.pdf
Under dash, I do have a tap into the 12v part of the ignition switch, I just havent used it, as I was going to use it to power a tach. But, since I went with a new fuse block, I dont need it. Should I then simply just use that tap as the 12v source? What about the old ignition wire (+ coil?). Just leave it un-used?
http://www.msdignition.com/pdf/6 series/6series.pdf
Under dash, I do have a tap into the 12v part of the ignition switch, I just havent used it, as I was going to use it to power a tach. But, since I went with a new fuse block, I dont need it. Should I then simply just use that tap as the 12v source? What about the old ignition wire (+ coil?). Just leave it un-used?
Rusty67
Dirt-Old 20+Year Member
BullittStangV8
Founding Member
S-Car-Go
Member
The "I" terminal on the starter solenoid will give you a switched 12v source. I ran a wire under the radiator (followed the voltage regulator wires) and mounted the MSD by the radiator overflow.
Rusty67
Dirt-Old 20+Year Member
Don't run too many things off of this. If you want to run a lot of items off of this source you can use it to send signal power to a relay and get the power from the relay instead.
Tim65GT
Active Member
The + coil wire and the I terminal on the solenoid are the same. They get their voltage from the resistor wire off the Ignition Switch C (coil) terminal.
When cranking though, the solenoid provides the full voltage to the coil through the I terminal. Once running the coil receives 6-9 volts because of the voltage drop across the resistor wire.
You may measure 12v at the coil or I terminal with the key on and the engine not running. It depends if the points are open or closed. If the wire is removed from the coil, same thing, there is no load on the resistor wire, so there is no voltage drop. Get it?
For the MSD the main current draw is through the heavy red wire. The smaller red wire goes through the switched source (coil +) and does not draw alot of current, so leaving the resistor wire in is fine. It's just a "turn on" signal.
If you are wiring an electric choke (or other high current device) however, you would have to go through the firewall directly to the "C" terminal on the ignition switch. I would use a relay to prevent excessive current draw from that terminal though.
When cranking though, the solenoid provides the full voltage to the coil through the I terminal. Once running the coil receives 6-9 volts because of the voltage drop across the resistor wire.
You may measure 12v at the coil or I terminal with the key on and the engine not running. It depends if the points are open or closed. If the wire is removed from the coil, same thing, there is no load on the resistor wire, so there is no voltage drop. Get it?
For the MSD the main current draw is through the heavy red wire. The smaller red wire goes through the switched source (coil +) and does not draw alot of current, so leaving the resistor wire in is fine. It's just a "turn on" signal.
If you are wiring an electric choke (or other high current device) however, you would have to go through the firewall directly to the "C" terminal on the ignition switch. I would use a relay to prevent excessive current draw from that terminal though.
S-Car-Go
Member
Learn something every day. I would swear I saw 12v with the car running, but it wouldn't be the first time I was mistaken.
So with the car running you should see a 3-6v between the pos battery terminal and the I terminal (and 6-9v I to ground)? I need to check this as soon as the car is on the road again.
So with the car running you should see a 3-6v between the pos battery terminal and the I terminal (and 6-9v I to ground)? I need to check this as soon as the car is on the road again.
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