tach control

MSD Digital Ignition Programming & Troubleshooting, Playing with Dots, Slew and other fun toys for traction challanged racers

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zephyrc
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tach control

#1 Post by zephyrc » Sun Jul 11, 2010 11:14 am

i have an msd 7530 and the shift light is triggered from the box.. the shift light flickers very faintly when the motor is running but lights perfectly every time when needed.. the shift light is autometer led... is this a problem with the shift light or the box

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Re: tach control

#2 Post by John_Heard » Sun Jul 11, 2010 4:41 pm

If I remember correctly, the box grounds the lamp. Probably ought to check the wiring and perhaps the light to make sure it's not touching ground somewhere. If it's not, then sounds like there is an issue with the box.

Try unhooking it at the box when it's flickering and see if it stops, or still does it.

zephyrc
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Re: tach control

#3 Post by zephyrc » Mon Jul 12, 2010 11:52 am

john,, it stops when unhooked from the box,, but i thought it was because i took away the ground..the shift light is the one that came attached to the autometer playback tach,, i no longer use the tach as it was about 400 rpm wrong at 1500 rpm..when the light was on the playback tach it worked fine but was reading the wrong rpm,, i took the light off the tach and am now using it in a stand alone capacity..,, could the shiftlight be incompatable withe this way

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Re: tach control

#4 Post by John_Heard » Mon Jul 12, 2010 12:27 pm

No, it ought to be ok to use with the MSD Box.

It should have stopped when you unhooked it from the box, unless you had a bad wire somewhere and it was grounding out. What's probably going on is the MSD box has an issue leaking a tiny bit of current when that output is off. It probably doesn't affect anything but the light. It doesn't take much current to light the LED, you probably wouldn't even see it if the shift light was a incandescent bulb.

You might be able to put a resistor across the terminals on the Shift light to make it quit doing this, but to avoid any warranty issues you may want to call MSD up and discuss first.

zephyrc
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Re: tach control

#5 Post by zephyrc » Mon Jul 12, 2010 5:17 pm

john,, when you say put a resistor across the shift light terminals,,any idea what size, type resistor and where, would it go across the two wires live and ground.. by the way thanks for the help

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Re: tach control

#6 Post by John_Heard » Mon Jul 12, 2010 7:05 pm

Probably won't take much, say 500 ohm 1/4 watt resistor - yeah across both wires on the shift light. If you have a test light, you can simulate if this will work by hooking it up to the hot and the MSD shift light wire (ground) along side the LED shift light. If that makes it go out (which is should if it's what we think it is) then the resistor with one end hooked to positive and one to negative of the shift light wires will work.

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