MSD 6AL Won't Stop Until I E-brake

Discussion in 'Street/strip 400/430/455' started by knucklebusted, Oct 29, 2017.

  1. knucklebusted

    knucklebusted Well-Known Member

    So, I swapped an MSD 6AL and a conversion distributor into my car late last year. Some might call it a small body HEI. I bought it off a board member and it worked great for a while but now I'm getting an oddity that is confusing. For clarification, the 6AL is wired to the battery full time and it turned on by the ignition wire that normally goes to the coil in my case.

    So, if I start it and pull out of the garage and shut it off, it turns off. If I drive it to town and shut it off, the alternator light comes on and the car keeps running. I can open the door and nothing changes. When I hit the e-brake, it will die like I turned the key off.

    Anyone else seen anything like this? It didn't do it at first and won't do it until it has been driven a while. Could this be a ground problem? It is grounded directly to the battery. Could it be a capacitance issue that the e-brake light in the dash does something to? I've not investigated too much as it something I figure I can always remove if it get too annoying but I like a good mystery.
     
  2. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    you need to Install the diode that comes with the msd. very common issue. the alternator is feeding back and keeping the msd turned on. msd even ships the diode with new boxes..
     
  3. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    X2

    MSDRunOn.JPG
     
  4. knucklebusted

    knucklebusted Well-Known Member

    So, I bought it used. I've found specs at 1A/100V for the diode but I'm unsure how it needs to be installed. Are you familiar? Does it get spliced into terminal 4 on the voltage regulator, as in cut it and solder this in? I hate to cut on my wiring harness if there is another option.
     
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Yes, and you need to orient the diode correctly so it only blocks voltage in one direction. Maybe someone knows a better way?
     
  6. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I'm not sure which where to put it on a rig with an external regulator. I've upgraded mine to an internal unit. msd has excellent wiring diagrams on their site. just about every combo imaginable is covered.
     
  7. Mark Demko

    Mark Demko Well-Known Member

    I had the same issue.
    If you still have the original electro-mechanical voltage regulator replace it with an electronic regulator.
    WAAAAAy back in the late 80's I replaced my bad regulator with an electronic one, then years later I installed an MSD 6A, no issues.
    Fast forward to today, replaced my alt. and regulator, the regulator I got was the "old style" electro-mechanical, I didn't think anything of it, installed it and ENGINE WONT SHUT OFF AND ALT LIGHT STAYS ON!
    Put a new electronic regulator on there and all is well:D
    I have no idea if there was a diode with the MSD back when I bought it new, if there was, its long gone now.
     
  8. knucklebusted

    knucklebusted Well-Known Member

    How can I tell an old style elector-mechanical (which I'm sure I currently have) from the electronic regulator? Is there some obvious external sign?
     
  9. Mart

    Mart Gold level member

    20171030_090104.jpg I had that problem also when I switched to Demon or Holley HP chokeless carbs.
    Seems the Holley 750 with electric choke I was running, was drawing enough current that let the engine shut off, not with the other two chokeless carbs.

    You can get an assortment pack of diodes at Radio Shack. Four diodes of each resistance in package.
     
  10. knucklebusted

    knucklebusted Well-Known Member

    I have the diode. I just don't want to hack up my wiring harness. I have found that Advance carries a pigtail for a voltage regulator that I could use to construct a short jumper or I might take my voltage regulator, cut the 4th terminal and solder the diode inline to it. I'll investigate further this weekend.
     
  11. Mark Demko

    Mark Demko Well-Known Member

    The electronic regulator that I have now has a shallower cover than the original, plus the cover is plastic.
    The parts store ( O Reilly's) list it as electronic, its made by BWD
    Heres a pic of it IMG_2180.JPG
     
  12. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    It's a solid state regulator. That is the replacement they sell these days. I have an internally regulated 12SI alternator. I have never experienced run on with my MSD Digital 6, and I have no diode installed.
     
  13. knucklebusted

    knucklebusted Well-Known Member

    OK, I've figured out how to tell the electronic from the mechanical. The mechanical ones have resistor wire coils on the bottom where the electronic ones are just terminals without anything on the bottom, all under the cover. I'll pick one up this weekend and see how it goes. Might even help my headlight dim at idle issue if I'm lucky.
     
    Mark Demko likes this.
  14. Mark Demko

    Mark Demko Well-Known Member

    Make sure its the electronic type, as I was sold the old style initially, so both types apparently are still available.
     
  15. sriley531

    sriley531 Buckle up, this could get rough....

    x2
     

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