Re: bypassing fusebox for rear demister
Obviously it is a common problem and you need to check for shorts / burnt out connectors (eg begind the glove box) first... however I have had a similar thought in mind!
As the std wiring clearly isnt up to the job, what I was thinking of doing was using the existing feed to supply a fused relay at the back of the car. I would then take a fee directly from the battery using decent quality wire. As the battery is back there this has to be easy enough to do.
Doing that would maintain 90% of the original wiring and operation, simply re-routing the main current load to come direct from the battery...
I'm going to look at mine this weekend, it doesn't work at the moment, and I need to find out why first. I will probably fix a problem once but if it fails again I will definitly do the above as it should be a guaranteed long term solution.
Hope that helps!