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.

 

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"

No, but I know how the tachometer gets its signal from the ignition circuit.

I left my wiring completly intact and bridged over the resistor block. Kept it as retro as posible.

The tacho is connectd to the blue wire through a resistor under the dash. Are you sure its connected properly and the rssistor is ok?

 

TIU280Z1976_REV2.pdf

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 April 12, 20186 yr by Halo8u

Basically the negative side of the tachometer connects to the negative side of the coil through a 2.2K Ohm resistor. The stock wiring has the resistor built into the circuit at a connector.

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 April 12, 20186 yr by Zed Head

Gotcha. Will definitely look into that. And thank you. Hearing it crank was such an amazing feeling. It sounds amazing.

"Do it in a Datsun"

https://drive.google.com/file/d/173O2wGRXimaOVfmhbjCkzBm8E5NG1l-_/view?usp=drivesdk

 

This is the exhaust clip of it running. Not really important to the thread but exciting and would like to share it with the people who helped me to get it started.

 

"Do it in a Datsun"

 

 

 

 

Is this what you were talking about?

"Do it in a Datsun"

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...

Edited April 13, 20186 yr by Zed Head

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.

Gotcha. I'm not too good with colors. I'm colorblind haha

"Do it in a Datsun"