The tach resistor is clearly pictured in Post #17, first picture of this thread... >>> https://www.classiczcars.com/forums/topic/62552-78-280z-turns-off-with-turn-signalreverse-lights/

<<<<< Off center to the right, the *BLACK* rectangular plastic housing shown here is the tach resistor.

Thanks to @Usain_Boat for uploading his picture.

Edited July 29, 20195 yr by wal280z
clarification in bold

What a great picture! … and thank you! I found the resister! It appears to be in the factory bundle still taped and still connected. Could the resistor be bad?

Since you've found it you might as well check its continuity to the coil's negative terminal.  You can do that by turning the key on and checking for voltage at the female part of the bullet connection after removing the resistor.

It's more likely that you just have a bad tach though.

Thanks Zed Head... I will check that out first before condemning the tach. Thanks for the diagram. 

 

BTW.... I don't know what this resistor does above the coil. Please see the picture I just took..... there may be no connection to my tach issue but it looks like it is coming apart.

That's not a resistor. That's the condenser for suppressing radio noise.

LOL! Well that's not an issue.... still has the stock radio!