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Discussion Starter · #1 ·
Are your wiring diagrams handy right now? If you would please, look at the "trigger" wire going to the tachometer and tell me if it's connected to the coil + or the coil - terminal. Thanks! I may have wired my MSD tach adapter using the wrong diagram....

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Gregg Haskin
72 Chevelle SS
ZZ502 Crated RAT
Muncie M-20 4 speed
TEAM CHEVELLE #726 ACES #4486
"PROUD TO BE AN AMERICAN!"
“What the heck are all these extra nuts & bolts for?”

My 72 Chevelle SS Restoration Website: www.wcvt.com/~ghaskin
 

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Gregg
It's always the - side. The - side is (or was) the side the points go to. The + side of the coil (transformer) has a constant DC voltage to it. The open-close or on-off operation of the points or hall element generate the pulsed signal for the tach and create the AC input to the coil.
Lots of words (maybe too many) but I hope that was clear enough for you.
 

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Discussion Starter · #3 ·
Now I'm REALLY confused! I unhooked the MSD tach adapter box, and connected the brown wire coming out of my wiring harness to the negative side of the coil. The tach stopped working all together. It had been connected to the + side of the coil all along, although the tach operated erratically. I then installed the wires from the tach adapter box per the installation diagram for cars using + side of the coil, the tach would not work at all.

Then, to top it all off, the pink & yellow wires in my engine harness began to get very hot to the touch. These are two wires that are bonded together at their ends with a "coil style" spade connector. So far, I've not connected these to anything because the car starts & runs without doing so. I had posted a topic months ago asking if anyone knew what these two wires did, but no one had input. I didn't have time to check if there was voltage present in the wires, but why would they get hot without voltage? HELP!!!

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Gregg Haskin
72 Chevelle SS
ZZ502 Crated RAT
Muncie M-20 4 speed
TEAM CHEVELLE #726 ACES #4486
"PROUD TO BE AN AMERICAN!"
“What the heck are all these extra nuts & bolts for?”

My 72 Chevelle SS Restoration Website: www.wcvt.com/~ghaskin
 

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Gregg
Not an MSD expect and somebody hopefully will correct my errors. On page 10 of the MSD instructions it shows the wiring for a points style set-up. Diagram shows a separate output for the tach on the side of the box. With the MSD the tach output should not go to the + coil. Even though the tach originally when to the - coil, MSD shows a separate output for it out of their box.
MSD's red wire should be a full 12 volts. Have you run a separate switched 12 volt line for it?
The pink and yellow wires sound like the original + coil wires. With your MSD box this connection is not needed and should be sleeved and tied back. All this is assuming you ran a new wire to the MSD red wire. If this is getting hot, disconnect the yellow wire off the starter, sleeve that and tie it back. Does that stop the burning.?
 

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Discussion Starter · #5 ·
John-

I've wired my MSD 6AL box & coil as per instructions on page 11, top diagram, for use with an MSD magnetic pickup distributor. The heavy red is to the Batt, the small red is to my fuse block terminal marked IGN. I'll attempt the removal of the yellow starter wire tonite & post results. If I remember correctly, I believe I did try hooking the brown trigger wire to the MSD tach output port with no results. Thanks for hanging in there with me on this!

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Gregg Haskin
72 Chevelle SS
ZZ502 Crated RAT
Muncie M-20 4 speed
TEAM CHEVELLE #726 ACES #4486
"PROUD TO BE AN AMERICAN!"
“What the heck are all these extra nuts & bolts for?”

My 72 Chevelle SS Restoration Website: www.wcvt.com/~ghaskin

[This message has been edited by riskyvt (edited 03-07-2002).]
 

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"I then installed the wires from the tach adapter box per the installation diagram for cars using + side of the coil, the tach would not work at all."

Maybe I see your problem. If you bought the 8920 adapter you should be wiring it up according to page 2 of the 8920 downloadable instructions. Your tach is a voltage triggered tach that originally went to the - side of the coil not the +. Since you have the magnetic pick-up, the 6L box does not use the white wire. This is the points input. Sleeve this wire back. Also look at the red and violet wires on page 2 of the tach adapter 8920 downloadable. They are wired differently that page 1. From what I can tell page 2 of this downloadable is your set-up. Again no expert. I'm just reading all this stuff.
Points Forever!
 

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Discussion Starter · #7 ·
I just got back from the shop. Let's cover what I believe you solved with my "hot" wires. As you suggested, I disconnected the yellow wire at my starter solenoid, pulled it back & taped it off. The yellow & pink wires in my engine harness are now cool to the touch. Just to check, there is voltage at these wires, running at the alternator's output #'s of +/- 13.8V.

Now onto the tach problem. Just out of curiousity, I have wired the MSD 8920 tach adapter using one wiring diagram, then the other. Neither solved the problem. The ONLY way I get the tach to read any RPM is if I connect the brown trigger wire to the + side of the coil. I agree with you that it SHOULDbe connected to the coil - side, as I checked my wiring diagrams last night. Is it possible the tach is messed up? I assume that's not the case because I can get it to work on one side of the coil, then not work on the other....


------------------
Gregg Haskin
72 Chevelle SS
ZZ502 Crated RAT
Muncie M-20 4 speed
TEAM CHEVELLE #726 ACES #4486
"PROUD TO BE AN AMERICAN!"
“What the heck are all these extra nuts & bolts for?”

My 72 Chevelle SS Restoration Website: www.wcvt.com/~ghaskin
 

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Well from all the stuff I read, you should be able to get your tach to do something if you hook it directly to the MSD box output. The filter is only there to kill some of the noise. It's not a great idea to keep hooking it back up to the + coil. Not sure if the MSD box output is going to like that. It's the wrong spot anyway.

I have a thought. It's probably a bad thought and I have never tried it. If you try it you may want to ask around to see if there's a flaw in my idea before you do. Here goes.
What would happen if one takes another Chevy points distributor car and moves it next to yours. Jumper both cable the battery terminals between the cars so they have a common circuit. Same as jumping a car.
Jumper your brown tach wire (tape the connection) to the negative (-) coil connection on the second car. Running the second car should make the tach move if it is functional (key ON in your car but not running. Just a thought, nothing more.

If disconnecting the yellow wire from the R terminal stopped your wire from heating up, think I would look into a new solenoid.


[This message has been edited by John_Muha (edited 03-07-2002).]
 
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