I just got my 427 put all put in and after running the car for a while, it won't shut off when I turn the ignition to off. However, if I unplug my alternator, the car then shuts off when I turn the ignition to off. Do I need a new alternator, or is my ignition switch bad in my column?

Thanks,
Matt

 

It sounds to me like your ignition switch is bad. Turning off the ignition should shut off power to your coil. You may want to unplug your coil when the car isn't running for now as it isn't good for them to have power for a long time when the car isn't running.

-dath

 

 

Ya, know, somthing tells me we had this same issue when we swapped a Vette engine into my '57....

It's been 25 years...but as I remember, my dad cut a resistor wire and shortened it, or bypassed the ballast resistor somehow..and it allowed voltage to stay on the coil.


I spoke with him about this not too long ago as we were shooting the breeze, and he seemed to recall the problem was mis-wiring on the starter solenoid.

I know my reply sounds confusing, but he remembers it one way, and I the other.

 

mine did that when I installed my MSD ignition box, there was enough voltage to keep the box energized. had to install a diode at the alternator

 

Haven't seen that one in a while.....

Yes, the MSD sometimes has that issue and needs an external diode installed.

If stock type ignition, it's very possible you have a diode trio bad within the alternator. It's easy and cheap to replace and check if you have an ohmeter.

Let me know if you need help checking it out


JIM

 

I am running a MSD with a 6AL box. Where can I get an external diode? Are they hard to set up?
Thanks,
Matt

 

Hi Matt...you have mail,,but I figured I'd post this here for anyone else that might have this issue someday.

Do you still have instructions that came with MSD? If so look on page 8 for a diagram.

Usually they come with the diode in the little parts bag just in case.

I forget...what year is your car? If it's an external regulator you install diaode in the wire going to the #4 terminal on regulator.

If internal regulator, install it on the littlest (brown) wire coming off alt plug.

If nothing else, you can put it inline to the smallest red wire going to the MSD.

The issue is the current going to the charging light on the dash. The bulb actually acts as a controlled resistance and as long as current is the same on both sides, it stays off...when it changes it "realizes" it is discharging and turns on. The design of that sytem will allow current to "backflow" to MSD to keep box turned on. You need a diode installed to keep it from being able to do that.

Remember. a diode is a "one way" switch, and must be installed correct direction to work right. There is a color band on one end and it should be installed that band facing either the regulator or alternator or MSD box.

If you don't still have instructions, ck MSD site..I think you can download them from there.

If you need to get one, go to Radio Shack....you need a 100V/1amp diode. Should cost about 25 cents or so. Who knows, at Radio Shack..maybe a buck.

Hope this helps.



JIM
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Jim,
I didn't recieve a diode with my MSD for some reason. In your reply you said I can use a 1A-100V diode...I can get a 1A-200V locally, but in the intsruction manual diagram it shows a 1A-400V. Can I still use the 1A-200V?
Thank You,
Matt