Here's my basic understanding of electrics [shoot me down if I'm wrong]
The new fuses will have lower ratings than the old single fuse
fuses are rated in Amps
Amps = current flow
current flows through wire circuits and gizmos
if circuits flow through a common fuse then the current of circuit 1 and circuit 2 are both flowing through the fuse at that single point
if circuit 1 = 4 amps amd circuit 2 draws 14 amps - total amps going through the fuse would be 18 amps - in that case a 20 amp fuse would do the job
but split the two circuits and put an individual fuse on each one...
circuit 1 = 4 amps - a 5 amp fuse will do the job
circuit 2 = 14 amps - a 15 amp fuse will do it
You need to determine the current draw for each circuit and supply an appropriate rated fuse to suit. The combined total of all the new fuses should add up to close to the old single fuse rating.
If this is too confusing then please seek expert assistance. Under dash electrical fires due to poor wiring is not at all uncommon in these old cars.
