How is this:
When chasing electrical issues in our cars, or adding circuits, it is important to take into account the fact that the fuse blocks in our cars double as power distribution.
This picture is from a 72 - later cars are a little different - but this shows that the solid red area behind fuses 4 & 5 incorporates six spade lugs (one has a fat red wire and another has a fat black wire) that are all tied together. Power is connected from the battery here, and all six of the spade lugs in this area are connected, so this area of the fuse block distributes unswitched power before the fuse. Note that these circuits are connected without regard to whether fuse 4 and/or fuse 5 is in place.
Similarly, the solid green area above fuses 6 & 7 has three spade lugs that are all connected. In the fuse block pictured, all of the spade lugs have solid green wires attached to them. Electrically, these are connected to the ignition switch so they function to distribute switched power before the fuses.
These distribution connections are illustrated in the wiring diagrams in the owners’ manual and the blue books (but not in the nice color blown up version Prospero sells on ebay), but you have to look really closely to see them.
There is also distribution after the fuses. By way of example, the unswitched power area below the fuse, delineated on the back of the fuse block with white diagonal stripes across a red background, contains three spade lugs that are connected after fuse 4. Thus, the circuit connected to that area with the connector with one red/white wire is connected to the circuits connected to that area with the double red/white wire. Pulling fuse number 4 disconnects all the circuits in the red/white stripe area from the circuits in the red area, but the circuits in the red/white stripe area remain connected even if you pull the fuse. The red yellow area has two lugs that would act the same way after fuse 5, but there is only one wire attached to that area (red/yellow).
I believe on later cars that unswitched power is distributed across fuses 5 & 6, with switched power distributed across 3 & 4.
It is imperative that consideration be given to these connections when trying to isolate the circuits that go through any of these fuses.
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