First of all, I know that most of the fuel gages are not very accurate. However, mine was pretty accurate until lately. Now it will show 1/2 when it is close to empty. How can I tell if it is the sending unit or the gage? Search the manual and could not find any info on troubleshooting this problem. Gage has started showing signs of condensation under the lense lately. Anyone have any info on voltage output for the sending unit?