I'm trying to get to know my fuse and relay boxes better. They're labelled, but the labels are mostly acronyms and shorthand, and googling any particular acronym gives a lot of mentions of common tasks on forums but not any definitions or explanations (at least not that I can find).

I think it's probably easier to ask them all together and create a definitive go-to guide than have over a dozen questions which for an expert are absurdly easy with potentially one word answers. Maybe a great answer could help a novice like me understand how the different items interrelate. Note that StackExchange policy on "list questions" are that they're okay if they're clearly bounded and finite, like this, it's never-ending lists with an unlimited number of possibilities that are "too broad".

These are specific to my 1998 Toyota RAV4, but it'd be good to have a definitive universal resource, so please comment and/or feel free to include in answers any common ones for other makes that are missing.


  • E/G Main
  • H-LP
  • ST (I suspect this controls the starter motor but could be wrong)
  • EFI (95% sure this is "Engine Fuel Injection")
  • MG/C
  • DIM

Fuse acronyms are all detailed in the owner's guide, which for this model is available online, but relays are not detailed in the owner's guide at all.

  • 2
    h-lp would be headlamps, efi is as you say or electronic fuel injection, mg/c is for the air conditioning compressor magnetic clutch, st is for starter.
    – Ben
    May 3, 2016 at 10:55
  • 1
    Never seen these things in user guides. Service guides - maybe. On Volvos DIM is the Driver Information Module, aka the instrument panel, aka dashboard. Could also be the for the headlight dimmer switch. May 3, 2016 at 12:02
  • @Ben, please answer questions with an answer. Just because you don't know all of them doesn't mean it isn't a good answer.
    – JPhi1618
    May 3, 2016 at 13:31
  • And I thought Egyptian hieroglyphics were hard....
    – Moab
    May 3, 2016 at 15:49

1 Answer 1


Legend to Codes

E/G - Main is the relay for the Radiator fans.

EFI - Is the electronic fuel injection relay.

DIM - is the headlight dimmer relay.

H-LP - is the headlamp relay.

MG/C - is the air conditioning compressor magnetic clutch relay.

ST - is the starter relay.

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