I have a 1984 hurst olds, the tachometer is the stock rally cluster pack tachometer and the RPMs are reading wrong, how would I go about fixing this? I've heard about soldering a switch in the back of the cluster somewhere.... The gauge reads about 1500 rpm at idle. And I know my idle speed is not that high. This is my first post here, thanks for any help!

 

If it is not a show car remove the tach and install an aftermarket one. Problem solved.

If it is important to maintain the stock appearance try swapping in another used OEM tach and see if it also reads high.

 

If you remove the instrument cluster you will/should see an orange colored adapter (small) that plugs into a socket on the back tach side. These were notorious for coming loose and making the tach read approx. double. You can fiddle with the adapter or bend a wire and solder it on the 2 small metal tabs. Here is a link to view...not in color but should provide some good info. Used this fix a LONG time ago and all is still well with mine.
http://tech.oldsgmail.com/eint_tach_fix.php

 

----wow thank you! That's exactly what I needed!

 

Great suggestion, but I do want to retain some of the OEM parts on the car, as I am restoring it little by little, although it is far from show quality, thank you again for your suggestion!