So, I am fairly stumped and I’m hoping someone can point me in the right direction. Purchased a 1986 Firebird with a 350 swapped into it , original 700r4 with speed sensor in the end. The gauges all worked besides the speedometer . Figured it was just a sensor issue and replaced it , gears still looking good I reinstalled . To my dismay it didn’t fix my issue. I removed the connector to the sensor and tested it . I got 3 volts on the one tip and 4 volts on the other . Looking up the line I found that someone had cut the original wires and put in new wires. But they had left the old wires hanging and with a charge ! Not very high voltage but still there . We tried reconnected the factory purple and yellow wires together but that didn’t appear to fix the issue. I’m hoping if I follow the wires up and look I will find something to fix . So I am curious. After some research I have discovered there is a buffer box and a fuse? And then the speedometer gauge itself . I am curious. Where exactly are the buffer box and which fuse is the correct one to look for? If it comes down to it I will remove the gauges themselves but I’d really rather not disassemble the upper dash if I don’t have to. Any help is greatly appreciated . If anyone has any idea on proper locations to test , proper voltages I should have . And so on so forth on what exactly I’m looking for I’d greatly appreciate. It is a 1986 Firebird with a swapped in 350, and the original transmission. I have already found a few issues with this car from the previous owner and just want to see if I can fix this !

 

First check: Ground wire at Speedo Buffer.

https://www.thirdgen.org/forums/elec...ml#post5614502

 

will do this evening! I really need to look at the buffer anyway due to some odd wiring done by the previous owner