Hey Keith, Just wondering....... you say the fuse block is hot? All the fuses? could you have a poor connection of the power or ground to the fuse block.... or withing the block itself ?

I have now replaced the regulator for the second time and now the voltage across the battery is between 14.5V - 14.6V when running as opposed to 14.9V - 15.2V. The dip problem is still there and the engine still bogs at low throttle.
What is the other relay in the box where the regulator is located?

the dip in power seems to be across the board, all circuits are affected by any one.
IE: brake lights dim headlights
brake lights dim dome light
cigarette lighter dims dome light
fan dims dash lights
and so on..
the dip is temporary, like a 50% "brown out"
then up to the previous level
if the revs increase there is a slight increase in fan/light power
This happens when the car is not running, as I said before.
I forget if I mentioned that I jumped the power wire from the battery to the fuse box with a new wire and this changed nothing.
Also before I said that one fuse and fuse clips were hot to the touch, but removeing that fuse changed nothing.

I've reread this post and I have no more ideas. Can you please refresh my/our memory as to when the lights dim?
If pushing down on the brakes dims the headlights, have you tried holding the brakes down while you disconect each taillight?

the problem is present when the car is not running as well.

Somethings still not right with the charging, 15V is way too high.
Check at which point he reg is sensing batt voltage.

The alternator and regulator are brand new

Your voltage across the battery terminals with the engine running should be 13V9 to 14V3 ideally.
Over 15V as you said you were getting is way too high. If your rotor circuit in the alternator is fed full field current ( causing overcharging)it will overload the engine and cause it to stall. This will also drop ignition voltage. My advice is get the alternator and regulator tested together by an auto-elctrician or mechanic to be certain.

Just to put some more info out ther on this problem, I took out each fuse individually testing to see if the power dip was bypassed by eliminating the fused circuit and the problem was not affected. I then assumed it was pre-fusebox so I ran a new wire from the battery to the fuse box to jump what could be the problem and still the dip is there...

any more thoughts?

Nah man, the electric rear window is just for looks ... you can disconnect it.

What is an interlock? We don't know since Datsun 1200s (B110) did not have them. What I would do? I'd go to the library and check out a B210 repair book and see what the part is officially called, and how it's supposed to be wired up.

It sounds like somehing is damaged and needs to be replaced or disconnected.