The relay is just a dpdt 12v coil relay. This one is rated at 30 amps and sells for around $10.00 or so at ebay or amazon or many other places. You may need to add a jumper from one contact to the ground.
JQX-12F-2Z-DC-12V-30A-DPDT-General-Purpose-Power-Relay-8-Pin-LW-SZUS
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