i installed an autometer tach in my 93 dx hatch. I connected the green(signal) wire to the blue wire under the hood right next to the firewall on the drivers side. I read that in some how to thing. of coarse i connected power, ground, and light wires as well. The lights on the tach work fine and the needle on the tach moves when i rev on it but its not correct. ie. when i know im at well over 5k the tach only says like 3 or 2.5k. im thinking it could be from a bad ground but im not for sure that would result in my problem. any help?