I hooked up a VDO tach to my R terminal on my alternator, programmed it and now I have a problem. At idle it jumps all over the place sometimes up to 2000 rpm. It gets even worse if I turn on the head lights, radio ect. I have it grounded to the battery. If I give it just a little throttle It works fine. Do you have any ideas. The alternator is the older delco si 10 I think? And it is a "one wire". Is this my problem?