My speedo stopped working on my 73 GS. I'm pretty sure it's because the speedo cable that runs from the trans to the cruise control unit is bad. At least the end that screws into the CC is pretty messed up. I went on Rock Auto to get a replacement but seems like they only offer the cable that goes from CC to the dash unit. At least that is what it looks like from their pictures. Oddly they do offer different lengths. Anybody know where I can find the correct speedo cable for the car?
I would just measure the one that needs replacing and go from there. Had a speedo quit on me and ended up going down a rabbit hole. Replaced both cables-- top cable came from AutoZone and I found the lower cable on ebay. Speedo still didn't work and I found the cruise control had a bad gear. Got a used CC off one of the members here and everything was good... well, speedo was randomly off by a fluctuating mph and found out my speedo gage wasn't any good either so I had to replace that too. Then I realized someone had replaced the trans with a TH350 from a car with a highway gear rear end so I had to replace the trans speedo gears. Works good and accurate now.
All that stuff wears out, I had to replace EVERYTHING from the gears in the trans to the speedo readout approaching 300,000 miles. The CC seems to be the first thing to go, poor pot metal construct. Bruce Roe