Does any one know the part number for the plastic gaurd plug that goes in where you plug in the computer I guess it for protection I 've got twin 1994 mpi 502's missing one on one side or what its even called I could take the one I have to dealer but I thought some body might know thanks for any help

Not sure what you're refering to, but you should be able to find it on www.mercruiserparts.com

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Yes thats the cap. Does it it serve any purpose other than to keep plug in clean ? I plan to get one but does it hurt to run without it ?

no problem, I would smear some dielectric grease in the plug....

thanks for info