How to wire a relay? *HELP*

[Houston hb]

Originally Posted by shovelhd

The compressor draw is 16A, and the trailer circuit is 20A. If the compressor is running and you hit the brakes, you'll blow a fuse. Not good. Run a dedicated circuit.

i havent blown any fuses and its been 2 weeks using this compressor plus ive been using the brakes while its on it cycle. Isnt there another way?

[HH4]

The 7 pin setup should include a dedicated circuit that is always hot to supply power to charge the battery in a towed trailer. This should be wired and fused for at least 20 amps, possibly even 30 amps. It is not tied to either the brake lights on the truck or the electric trailer brakes. This should provide enough current to power the compressor. What size wire are you running to the compressor and how long is the run? Should be at least #12 but #10 would be even better. If you are not hooked to a trailer , the compressor should be the only draw on this circuit and braking would not have any effect.
Have you tried to run the compressor from a direct short feed right from the battery to see if it works ok?

[shovelhd]

Were you towing a trailer when you hit the brakes?

I'll admit I don't know about this dedicated circuit mentioned above. If there is one, it's 20A, that I know for sure. If it is dedicated and isolated from the lighting circuits, then that should work fine all by itself as long as you don't have a battery to charge on the trailer.

[HH4]

Originally Posted by KE5TCG

Make sure you use an in-line fuse, if/when you try this, with the fuse at the battery end of the wire. Like HH4 said, you need wire at least 12 AWG or larger, and the wire's insulation needs to be gas/oil resistant and its jacket designed for automotive use.

When I suggested a direct connection to the battery I meant to temporarily try it this way just to verify that the compressor was working properly, that's why I didn't mention fusing the circuit.

Unless you fully understand how the factory harness is connected and how it is protected the safest bet would be to run a new circuit direct from the battery and fuse it correctly as KE5TCG suggested.

You can then use the relay you mentioned in your original post to provide power to the circuit as needed. For example only when the ignition key is on.