What fuse to tap for Relay

Hey guys,

I'm putting my aux fuse block together and I'm looking for which fuse I should use my add a circuit on?

I want it to be on whenever the ignition is switched on.

Right now I've tapped the "EFI" fuse and it's not working the way I like.

Before I tapped it, I used my multi-meter and tested the lead on the add a circuit and it was perfect. Only had power when the truck was running.

This makes me think I may have wired my relay incorrectly. The diagram wasn't very good that came with it.

But still, I'd like your advice on what to tap into... Can't be more than 10 amos according to my add a circuit box

Thanks

 

Not sure which fuse... but your relay should be wired as followed:

85- Ground (-)

86- Add a fuse (12v accessory 10amp)

30- 12v battery fused (Max load of 30-40amps depending on relay... more power requires additional relays. Fuse correctly)

87- out to accessory fuse block

87a- NOT USED

 

Are you working in the "in cab" fuse box or the one in the engine bay?

 

Thanks! I wish my relay's packaging included that information. I remember reading those numbers and wondering what they referred to. If I switch 87 and 87a, will that matter?

Engine Bay. I should have stated that in my post. Sorry.

 

30 is common. 87a is Normally-Closed. 87 is Normally-Open.

When you take the relay out of the box and look at it, terminal 30 is connected to 87a.
When you apply power across 85 and 86, the magnet pulls the contact in and terminal 30 connects to 87.

There are legitimate uses for this, but in general, most DIY applications do not use 87a.

But make sure it is insulated because it DOES have battery power on it any time the ignition is off. I just slip an insulated connector over it.

 

Yes is will matter... if you connect your accessory fuse box to 87a, its like having a direct connection to the battery and defeat the purpose of the relay. See diagram below for visual explanation of what Rich explained: