I just scored a Factory Tach cluster at a bonyard up in Greeley, CO for $50 today. it was in a 77 blazer and I plan on installing it in my 75. I know that these clusters are not identical. For one, mine has an AMP gauge and the 77 has a Volt gauge. Also, the 77 has an electric oil pressure gauge where the 75 is mechanical. So, knowing there are differences I can't just mix and match from both clusters to make it work. I know I have got to use the printed circuit from the tach cluster to make the new smaller fuel gauge work. What I need to know is at the harness connection to the cluster if the wire inputs are the same, in the same location? If anybody has service manuals for both years that could scan a copy of the cluster wiring diagram would help narrow it down. I did a search here and struck out and also tried searching by Google and struck out too. Mikes 73-87 page had a good bit of info, but said nothing about installing a cluster from a later truck to an earlier one. Any thoughts or info in the wiring diagrams would be a big help!