Hi, I have a bit of a problem with my speedo on my '78 GTS, because it isn't working. The old sender unit was badly corroded and I took it apart, cleaned it and it worked briefly for about a week before dying entirely. I then bought a new sender and that's where it gets a bit odd: The new sender works (speedo moves), if I only connect the plug and spin the "pin" with a drill. It oscillates between 7V and 1V, when connected to the speedo. However, it doesn't work on the transmission (I checked and the drive is working - spun the wheel). I then connected the sender, spun it with the drill again and let it touch the frame, which causes it not to work anymore - It stays at 1V. However, I couldn't measure any short between the sender connections and its housing. The cable going to the speedo shows a resistance of 3.6 Ohms to the thread where the sender gets connected on the transmission. Is that correct or does the speedo have a short to ground? That wouldn't make sense to me either, because the sender works, if its housing doesn't touch ground. I look forward to someone, who knows whats wrong here...I really don't. Best regards
