I installed an amp and sub into my Executive and after the installation my speedo stopped working correctly. Sometimes it will work fine when its inbetween 50km/h - 100km/h, other times it is just really inaccurate or most of the time it just sits on 0.
I thought it could have been the amp power cable going through the same hole in my firewall as my speedo and somehow disrupting that but I removed it today to check if that was the problem and no luck with that.
Has anyone had any similar problems or know of what the problem is?

Im assuming if speedo isnt working there will be other things not working. Is the rest of the Dash Guages working alright.??? id be thinking you have cooked a fuse if you have been tinkering with the Electrics.

Did you remove the cluster to do the install? If so check all the connections, theres one plug and then it slides back into 2 pairs of pins.