Not sure if there is a Plymouth '73 there.
Have the Dodge '73 from there downloaded.
View attachment 1715530964
So as Redfish was telling us, there's several changes from previous years.
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Fuse cavity 6.
G5 & J2B is the wire identification. G probably is for wires to or relating to Gages. J is key switched power. J2B is probably the second branch from the Run circuit(s).
20 DBL = 20 gage Dark Blue, & 12 DBL* = 12 gage Dark Blue with tracer (white stripe)
So when you go to the diagram look for G5 and follow it to all its connections.
My suggestion is to save the fuses, disconnect the battery and check for continuity to ground (short). Clip one lead of the tester onto the G5 fuse terminal, the other to a good body ground. If there is a short, then start disconnecting the different items until the culprit shows up.
Seat belt buzzer would be an early one to check.
@RedFish and others may have better ideas.
