As all circuits in cars are pretty well fused after the fuse box, that is if there is a s short a fuse will blow no smell. A smell might indicate that it is either an unfused circuit to the fuse box or a badly installed aftermarket accesory that is un fused.Both of those would only provide you with a smell once not on an intermitent smell, unless it was a high current supply, ie from the alternatior to the battery, or battery to the starter but both of these would cause other problems in the car. Have you started using the heater recently as the temprature has dropped? I know that for the first few times I use my heater in winter it give of a bretty bad smell for the first few weeks. Or try checking you battery next time you smell the smell it is possible that you alternator has a fault and is causing you battery to over charge giving you a rather potent smell.
Hope this helps I am sure some one else will have a sugestion of other things to look for.
Adam