Alternator won't charge and reference wires are grounded

[snowball]

Hi all,

My 90 burb R1500 350 won't charge. battery always shows 12 V. I brought my alternator to be tested and it passed. I checked the reference wires by putting a multi meter and testing continuity and they're grounded.

Just wondering if there is a common place to look for the short or any advice.

Thanks!