Check your battery levels. Even if you have 12v, your cranking amps may be weak. Also check your ground leads. Dirty grounds will cause current and voltage drops as well. Take the anchor bolts out of the main grounds in the engine bay, degrease the connections and scrub them with steel wool. Look for sulphation/corrosion in the leads and make sure the battery terminals are in good shape. If the relays are rattling it normally means they are still working but there is an intermittent fault somewhere in the circuit.