I'm wiring in some accessories to my vehicle and my 1990 car has a basic fuse box with a plastic cover. On removing the cover I've discovered each fuse holder has a terminal which would be ideal for connecting a spade connector to tap into the relevant circuits (side lights and ignition on).

Thing is if I do this I will have to either leave the fuse box cover off or drill a couple of holes so I can withdraw the cover and also pull the wire and spade out completely if I ever want to.

It's at the back corner of the engine bay sheltered by a recess between the wheel arch and bulkhead/firewall and I will probably try and find a rubber grommet to fit around the hole to try and seal it off but obviously it won't be 100% watertight (I doubt the plastic cover is anyway).

Is this a bad idea?

  • Welcome to Motor Vehicle Maintenance & Repair! Commented Sep 23, 2021 at 9:36
  • 1
    If you are really worried about water ingres: en.wikipedia.org/wiki/Cable_gland
    – Martin
    Commented Sep 23, 2021 at 9:58
  • Good tip Martin, it seems there are a lot of cable glands on the market and I have never seen these before. I don't think there would be enough clearance inside the fuse box for one of these in my case but I'll definitely consider it.
    – ses
    Commented Sep 23, 2021 at 10:07

1 Answer 1


It probably wouldn't cause any issues, however, every fuse box I've seen has an area which would allow you to slip a wire between the cover and the body of the fuse box. The only way this wouldn't happen is if you're using too large a gage of wire. If the wire is too thick to fit between, you need to run a relay instead and use a smaller wire to power the connection to the relay.

  • Thanks I will double check but weirdly I don't think there's any holes and not enough clearance between the cover to get a connector on the terminals without drilling a hole. I guess by the nature of most covers having a hole somewhere none are 100% watertight anyway and I can always fabricate some sort of extra shield that fits over the general area to cut down on any accidental splashes of water from a hose or driving through standing water.
    – ses
    Commented Sep 23, 2021 at 9:59
  • 1
    There's always clearance ... you just have to find it. Even if you have to dismount the box and come up from the bottom. Commented Sep 23, 2021 at 10:09
  • Thanks that's a good idea too and I could still avoid having to disturb the other wiring that way. I'll give my idea a try first as it doesn't sound like there's anything fundamentally wrong with it and it would be easier to unplug and remove the accessory wires from the front if I needed too.
    – ses
    Commented Sep 23, 2021 at 10:34
  • You can do whatever you want to, as it is your vehicle. I guess I should have used stronger wording to try and dissuade you from drilling holes in your cover. You should really use this as a last resort, not a "oh, let's try this first". How's it going to look if you have wires sticking out of your fuse box cover or holes in it if you ever go to sell your vehicle? Really, there are much easier/cleaner methods to achieve your goal besides drilling holes in the cover. Commented Sep 23, 2021 at 11:58

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