If it's original it'll be a box mounted on the passenger side strut wall or near it. Like in this picture http://datsun1200.com/modules/myalbum/photo.php?lid=2298. If you have a multimeter try running it and watching the system voltage (battery terminals shoul do) and see if it goes much over 14V as you slowly bring up the revs.

thanks that helps heaps so where is the regulator?

If the regulator's gone it'll over voltage when you rev it up and that might blow the fuse by forcing too much current through the fuse that's blowing. The regulator steps down the field current in the alternator to control the system voltage. Otherwise the voltage output is roughly proportional to rpm. e.g. 12v @ 1200 rpm, 24v at 2400 rpm and pop in your case.

sweet will try that but that wouldnt explain why it blows the fuse when its reved up

With high revs + alternator light..

Sounds like voltage regulator or alternator issue.

Check the 2 large connectors that join the under dash loom with the engine bay loom. Look for corrosion or blackened connectors.
Clean them up with some wet/dry sanding paper first if they look dirty.

it wont let me put photos p for some reason if anyone has an email i can email them a picture of it so they can look at it and help out cheers.

i duno how to post up pictures im new to this lol.

it isnt a custom job it was in the car when brought ill get a picture up soon of it.
every time it blows the car idles real high and the alternator charge light comes on and the car misses.

Yeah the 'engine management' thing throws me off. There isn't really any engine management unless you consider the dizzie and coil as part of it.

You got a picture of the fuse board?

None of the stock fuses are labeled 'engine'. Is it a custom job?