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Transistor Module swap *PLS HELP*


Halo8u

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When you did your modification, you probably did not leave the tachometer connected to the negative side of the coil. The best way to do that mod involves leaving the stock wiring on the distributor, adding the additional wire for the HEI to trigger the spark, and disconnect the TIU from the wiring harness.

I'd offer to fix it at my house, but you're 5 hours away.

 

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When you did your modification, you probably did not leave the tachometer connected to the negative side of the coil. The best way to do that mod involves leaving the stock wiring on the distributor, adding the additional wire for the HEI to trigger the spark, and disconnect the TIU from the wiring harness.
I'd offer to fix it at my house, but you're 5 hours away.
 
Yeah, I rewired a lot of the entire area. Do you have the gm hei?

"Do it in a Datsun"

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I just hate how much the car was modified before I got it. It's been converted to Carb, and it throws a lot of stuff off. There are a lot of wires that would go to the ecu, which doesn't exist in my car. But when I get home I'll snap a pic of my wiring setup. Setup kind of shotty right now because I'm still testing. Once everything works properly I'll solder all joints and heat shrink, just to get everything neat and tidy. But being converted to carb throws me off a bit with a lot of these diagrams

"Do it in a Datsun"
 

Edited by Halo8u
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I had a tach problem with mine.  It just sat and quivered at about 500 RPM after the GM HEI swap.  I "reasoned" that the signal was too noisy and added a condenser/capacitor to the negative side of the coil.  It worked.  I'm not trained in electronics beyond a 101 course about 30 years and things I've picked up since then but sometimes my guesses lead to results, maybe for the wrong reasons.  I confirmed that the condenser was needed when the wire to the capacitor broke later and the tach stopped working.  I used a condenser/capacitor from the back of an alternator.  Worth a shot and can't hurt anything.

Forgot to say, congratulations on getting it to run.  Now you're hooked.  And you can check for voltage at the 2.2K resistor connection to see if the blue wire is connected.  It's easier than removing the tach to get to the plug.  The 2.2K resistor is a small lump in the wiring by the connection block area, down by the fuse box.  It's black and uses two bullet connectors.  Check for voltage with the key on.

Also, it might be that whoever took the ECU out also removed that wire.  Good luck.

 

Edited by Zed Head
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No, I'm pretty sure the wires are blue.

This is from a 76 diagram that a member put together.  I think that 75 is the same.  It's smaller than whatever is in that pile of tape in your picture.

Edit - wait, I see that the input wires in your picture are blue.  75 was the first year of EFI so they did some funky stuff.  That's probably it.

Edit 2 - a picture would be interesting.  The 76 and later parts are very nice, plastic covered resistors.  Almost a shame to cover them up in tape.  Yours looks clunkier.  You can measure resistance to verify.  Actually you don't even need to remove the tape, with the connectors right there.  But still...

image.png

Edited by Zed Head
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No, I'm pretty sure the wires are blue.
This is from a 76 diagram that a member put together.  I think that 75 is the same.  It's smaller than whatever is in that pile of tape in your picture.
image.png.060cc8e26157413790c975dd31b371bc.png
Gotcha. I'm not too good with colors. I'm colorblind haha

"Do it in a Datsun"

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