Power...but no power!

Hi, I hope someone can give some advice here as I'm so close to having this thing back on the road. Quick background - Mk1 Caddy with ABF conversion done by P.O, battery behind seat, cut off switch earthed to rear bulkhead.
Was working fine then one day went out and turned the key and nothing happened. No click, no dash lights nothing. Poked around at the fuse box, tested the main red wire coming straight from the battery to the back and it reads 12.6v. All the hot fuses show the same and all are intact. Main earth, the thick brown wire to the 2 pin then 4 pin plug is attached to the earthing cluster just above and seems intact. Reads 3.6v at rear of ignition switch which seems strange. So for some reason, there's power going in and spreading around the fuse box but nothing coming out.
I have no clue about electrics but have a multi-meter and if someone spoon feeds it to me I can perfom basic tests but have no idea what to test and what to check for.
Any guidance would be really really appreciated.
Thank you

 

3.6 at switch while cranking or just with the key on?

The isolation switches(red plastic key?) Are notoriously troublesome on rally cars , poor connections internally. Loop it to rule it out.

Otherwise you'll have to trace back the wire that only has 3.6 and see if there's a loose or corroded joint on it somewhere.
Could be a dodgy relay too.

 

Thanks, not sure what loop it means. Have just been out again and now shows 9.6v at the back of the ignition switch at off and then when i turn the key to acc/on it jumps up to 13.2v but still no dash lights or anything. Now seems theres power from the battery to the fuse box, power around the various pins on the fuse box and making it to the ignition switch but nothings happening. Very annoying.

 

Loop , as in join the two pins at the back of the isolator to rule it out.

Though it sounds like you have either a bad key switch, a bad earth point for your multimeter, or a bad supply cable from the fusebox to the key.

 

Thanks for the help. Went out this morning again. Plug that goes into the back of the ignition switch reads 13.6v at all of the inputs except for 2 which read nothing when the key is at "off". Same when I turn the key to "acc" and "start", no change in voltage but still no signs of life. Lots of people syaing it sounds like the switch but want to be 100% or as sure as I can be before I start taking it all apart. How would I test the switch?

 

Do you know which wire is the output from the switch? Loop a wire from the supply to that. If stuff works, the switch is faulty.

 

Hi, yeah got a picture with all the wires labelled. So just get a normal bit of wire, like an old cut off or something and put an end into each of the sockets of the plug?

 

Yes, use something as heavy a gauge as the wire to the plug.