This 80amp relay activates the fuel solenoid on years 94-98.5 12valve. If this relay is bad your engine will crank fine but will not start because the fuel is not getting to the engine. I always carry a spare in my truck. Also check your blue wire fusible link (available below) at the pos battery terminal before replacing this relay, if corroded or burned it will cause the same symptoms. This relay is physically different than stock, the mounting is slightly different. Electrically it is identical. Some stock relays are a double relay that includes the fuel heater relay. You can unplug the fuel shutoff side only and install this relay to avoid having to buying the double relay.