If you have an autometer voltmeter first off a hate to disapoint you but do not wire it to the switched wire on the back of the radio harness. I did that in my 96 jetta because yes it is a convinient spot but I was told by a PRO at Autometer that is not a good spot. You will get an incorrect reading. It will stay around 12-13V instead of 13.5-14.3. The resson why is it is getting the current draw from your head unit! Not what is actually running through the system. So with the autometer there are three connections on the back of the guage conviently unmarked One is for a switched power source, one is ground the other stays blank!!!! I think the one on the back left is the blank. I have the manual. Last if you have a bulb hook that up to a dimmer wire along with a ground. You should put the key in and turn to ACC and it should read 12-12.3. Start the car and it should ideally read between 13.5-14.3. Any thing higher or lower... lets just say its a good thing you bought a voltmeter. Get it checked out. Could be a bad cell in your battery or you may need a more powerfull alternater... probably if you have a lot of accesories like me. Especially a multi amped sound system. If you have any questions please AIM me at m4monaco good luck.