Technical +30 Definition

[frostbite]

hifolks,
Does anyone know what is +30 in Fuse Box Diagram?
For instance;
F18 - +30 Electronic Injection Control
+30 Fog Lights etc..

Another problem about my stilo is LooseConnection, I have this fault occasionally. But if I pull out the F18 from the fuse box next to the battery, the same Loose Connection appears. Literally the same. So does it mean that LooseConnection is about Electronic Injection Control? What do you think? What should be my next step to solve the problem?
Sorry to bother

 

[Davren]

+30 on wiring diagrams, fuse designation lists etc. is the 12 volt supply from the battery.
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