So I have been searching all night on the forums about the notorious non-opTachometer problems on these vehicles...It seems that the OVP relay is usually at fault when a problem like this occurs (especially when the AC goes out)....

I thought for sure that my problem would be the OVP relay, so I pulled the relay checked the fuse, then applied 12v to pins 15 and 31 and checked for continuity wala it worked and the relay opened and closed.... I put the relay back in and same problem, no tach/no AC....

I have ordered a new OVP Relay just in case, but is there anything else that could be at fault here? I am stumped on how the relay could be bad and cause these problems when it tests ok? Any other ideas on what it could be? Is there anything else that will not function properly if the OVP goes out?

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2005 SL65
1999 E300
1995 E300
1994 SL320
1988 560SL
1987 300TD
1982 300D
1955 300SL