Pre cat with alternator woes!

[v8jimll]

Hi all, the battery gauge and red warning light are telling me that the alternator is not working. I confirmed this with my trusty multimeter (12.5 volts when running), so checked the feed wire to the alternator and it only has 1.5 volts with the ignition on rather than 12v which is what I'm assuming it should be, where do I go from here?? Regards James