I have a 75 Cutlass Supreme with the standard fuel gauge with idiot lights. I bought a used Rallye Pack gauge and I thought I could just unplug the old harness and plug in the new gauge. The problem is, even though the wire colors are the same on both gauges, the location of the wires on the new gauge pack are in different locations on the harness. Do I have to cut off the old harness and splice the wires together matching color for color?

 

Do not cut anything!
A paper clip or jeweler's screwdriver pops out the wire terminals from the connector and you just rearrange them. A new one may need to be added for the tach input...

Read this article and you should be able to do the swap easily without splicing...
http://www.442.com/oldsfaq/ofmsc.htm...bodyConversion
Make sure you use the instructions for 73-77.
You need the oil and temp senders, available at you local parts store.

 

Thanks so much for the info.

 

Imagine that: I'm looking to do the same thing.Let me know if it works?

 

the 75 model doesn't have the tach in dash. I believe the harness is a molded rubber where it plugs in. I had to cut , soldier and splice mine in when i had a 76 442.

 

The best guidance I have found for wiring/rewiring the Rally Pack in 68-72 olds is from The Parts Place technical bulletins. The bulletin has very clear instructions on how to remove the pins in the female end of the instrument cluster wiring harness to reposition. This can be found here: https://www.thepartsplaceinc.com/tec...ly-information
The document is attached.