Under Dash Relay??

[72Thunder]

Hi all,

I have recently begun stripping the interior of my 1972 C10 and came across this relay under the dash above the fuse block, but to the left of the horn relay. It has a brown, blue, black and a possible 10ga. red wire (this one isnt hooked up) connected to the relay and all taped together that comes out of the driver's side of the firewall. Could anybody tell me what this relay is used for and what the wires are indicated as?

Thank you very much in advance!
Darcy