[BNaylor]

Welcome to AF.

Since you have a '98 model Intrigue with the SII 3800 engine position #18 in the engine compartment fusebox is missing from the factory for a reason. Reason being is that is reserved for GM cars like the Regal that have the L67 Supercharged SII 3800 because they have a two speed fuel pump. The relay missing is actually the fuel pump hi-speed relay and has nothing to do with your cruise control problem or the cruise control circuits.

On your cruise problem it could be the cruise control module or a possible odb-ii emissions related problem causing the cruise control to be disabled. Misfires will cause the cruise to drop off and certain odb-ii DTC error codes. You may consider getting it scanned with an odb-ii scan tool and hopefully some codes are stored in history.