I need help from you MSD guys

[Car #4]

With the key in the on or run position I have no power on the positive wire on the coil. There is power going from the switch to the MSD box, it’s the top red wire on the left side of the plug. Is the box shot or could there be something else? This box doesn’t have very many miles on it. I think it’s two years old, maybe three, but I haven’t driven the car much.

 

[Car #4]

I should maybe add that about three weeks ago the car died on the road and I waited about an hour for a tow truck. After waiting a while I tried it and it fired up then died. Wouldn’t restart. Five or ten minutes later the same thing. After we got the car home and the truck left I tried it and it started and ran. The next morning the same thing, it started and ran. Didn’t get back to it until today. I wouldn’t start at all. Then I started troubleshooting.

 

[tonysrt]

I have a light on my MSD box and it flashes when I turn on ignition for a few seconds and then goes off. This is without engine running. Sort of like a little trouble shooting.

 

[Curiousyellow71]

First thing make sure the large black wire is grounded good and the large red is going directly to the battery. Go directly to the battery w both if you have to to test it. When it randomly runs or dies that usually says there is a bad random connection.
Also check to see if the small red wire is getting power to turn the MSD on.
What distributor?

 

[Car #4]

I’ll check that. Thanks. I know there’s a light there. I’ll pull out the MSD book too. I ran out of time today, it’s wing night.

 

[Car #4]

First thing make sure the large black wire is grounded good and the large red is going directly to the battery. Go directly to the battery if you have to to test it. When it randomly runs or dies that usually says there is a bad random connection.
Also check to see if the small red wire is getting power to turn the MSD on.
What distributer?

MSD distributor. The large red? The one coming from the switch? Is the small red second from the bottom? It had power. Sorry, I’m not at the car right now, or even at home to run out and look.

 

[Curiousyellow71]

There are two red wires. One large wire should go directly to power. Not switched..power all the time. It needs all the voltage in can get.
Then their is a smaller red wire probably 16 gauge that goes to keyed power.
The large black ground if it isn't a good connection will also cause the MSD to randomly die or not start.
I just had a MSD do the same thing as yours and it had a bad ground.
With the MSD distributor the white wire is not hooked to anything, unless it is a "ready to run" distributor with a control unit in it. But their should be two (violet and green) wires connecting to the distributor from the msd if it is the typical style that just has a magnetic pickup.

 

[Geoff 2]

You have a MSD box, such as a 6A? These do NOT have 12v to the [+] side of the coil.
They have a thick red & black wires which connect direct to the battery. The thinner red wire goes to the ign switch.

 

[DanielSlocum]

MSD is great; unless it fails on the road somewhere. Then you are stranded/screwed.

 

[Rebelrouser]

With the key in the on or run position I have no power on the positive wire on the coil. There is power going from the switch to the MSD box, it’s the top red wire on the left side of the plug. Is the box shot or could there be something else? This box doesn’t have very many miles on it. I think it’s two years old, maybe three, but I haven’t driven the car much.

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View attachment 1691910

MSD is a capacitive discharge type ignition. The two wires that come from the box to the coil will have a lot more than 12 volts, more like 450 volts when running. When not running zero volts. See this video https://www.holley.com/blog/post/how_to_troubleshoot_an_msd_6a_6al_ignition_control/ go to 5.11 into video on spark testing.

 

[Car #4]

You have a MSD box, such as a 6A? These do NOT have 12v to the [+] side of the coil.
They have a thick red & black wires which connect direct to the battery. The thinner red wire goes to the ign switch.

Yes, it's a 6AL.

 

[Car #4]

@Geoff 2 @Curiousyellow71 The black ground wire runs to the battery and I cleaned up that connection although it looked good to begin with. There's a red wire coming from the switch and going to a post on the alternator and another wire from that post to the box. That's the big red one. It does not go to the battery.
Also, with the key off that post on the alternator is live. Should it be? Then there's always power to the box. Is that ok?
And, with the key on, the red light on the box is not on.

 

[Car #4]

I will reroute the power source from the alternator to the battery as recommended but could having it wired that way have damaged the box? I hope I haven't fried it. When this car was restored before I bought it it was wired with a Quik Wire kit and not all things were done as good as they could have been. The power source for the MDS a case in point. I'm still working out gremlins, this being one of them.

 

[Curiousyellow71]

I don't quite follow where the small red wire is getting power from in your description. It has to be switched power, It activates the msd when you turn the key on. It is what turns the car off/on. Usually it goes to a wire that would have been where a ballast resister was.. that would give the points power or the original ecu power. It should not run through the ballast resister if its still in place. The alternator post is live all the time and not switched.
Unfortunately a digital MSD does not have a great reputation for being durable.

 

[Car #4]

I don't quite follow where the small red wire is getting power from in your description. It has to be switched power, It activates the msd when you turn the key on. It is what turns the car off/on. Usually it goes to a wire that would have been where a ballast resister was.. that would give the points power or the original ecu power. It should not run through the ballast resister if its still in place. The alternator post is live all the time and not switched.
Unfortunately a digital MSD does not have a great reputation for being durable.

The small red wire goes to the fuse box and also supplies the electric choke. There is no power on that pin in the MSD plug with the key off but there is with the key on. That's the way it's supposed to be, yes?
I used my phone to video the box when I turned the key on and the red light came on for two seconds. The book says it should come on for one long flash. Maybe two seconds is their version of a long flash, I hope so. Can anyone verify that please.
I rigged up my test light to the positive side of the coil and it flashes like crazy when I go to start so power is getting to the coil.
Next I'll test for spark at the plug but that will take two of us and that won't be until this evening. If I have spark there then it must be a fuel issue I guess.
All comments are welcome.

 

[Curiousyellow71]

Do you have a timing light to check for spark?

The troubleshooting guide... says light should flash 5 times.???
If you have a 2nd set of hands to help.. check the voltage of your small red wire during cranking.
This should be helpful if you havent found it yethttps://www.holley.com/blog/post/ho...ext=With the key in the,as well as the ground.

 

[Car #4]

Ya that flash 5 times is if you haven't set up the rev limiter. I have done that so it should only give one long flash.

 

[Car #4]

Thanks for your help guys.

 

[ynst]

@Geoff 2 @Curiousyellow71 The black ground wire runs to the battery and I cleaned up that connection although it looked good to begin with. There's a red wire coming from the switch and going to a post on the alternator and another wire from that post to the box. That's the big red one. It does not go to the battery.
Also, with the key off that post on the alternator is live. Should it be? Then there's always power to the box. Is that ok?
And, with the key on, the red light on the box is not on.

"That's the big red one. It does not go to the battery."

That's you problem. Bite the bullet and buy another 6AL 'cause yours is fried. Most likely, the fusible link inside the 6AL is melted.
Connect the heavy red wire directly to the positive battery cable. Connect the heavy black wire to the engine block (or to the battery). DON'T connect the power wire to the (electrically) noisy alternator or the ground wire to the body sheet metal or you'll be buying yet another MSD in the future.