Help, Compressor wireing issue

I was given an omega train horn kit when I purchased my truck and i’m having some problems with the compressor. I wired my compressor to an accessories jack under the dash so it would only power on when my truck was on. I notice after a few attempts to use the horn that the compressor is not working properly. It powers up and runs for a few seconds they it slowly starts to die until it just has enough power to whine. I did a few tests and wire it directly to the battery and it runs powerful and strong with no issues. I put a meter on the accessorie jack and it shows 12v but when i connect the compressor and turn it on I can test it and it gets all the way down to about 8v when the compressor stops working. What in the world would be killing the power if its still a 12v power supply? Does it need a relay?

Thanks for any help with this problem!

AMPS AMPS AMPS AMPS. How the heck has this not blown the fuse in the truck?! Please tell me its fused because a fire comes next if it isn’t.

Yes, it NEEDS A RELAY so it can get power directly from the battery.

Also, this is posted in the wrong category. Try here:

Yes it has an inline 15 Amp fuse that has not blown. Thanks for the response I didn’t notice it was the wrong place I’ll switch it over.

Thank you