Chasing a Short - Where to Start?

I've got a short I'm trying to find in my stock wiring harness in the turn signal / backup lamp / gauge power / etc. circuit. (The circuit with the 14 amp fuse).

The fuse doesn't blow immediately after changing, but will blow within a couple miles of driving. Using the turn signals doesn't cause the fuse to blow, nor does the backup lamp switch (mainly because I never bothered to hook it up to my NV3550...). The original harness is in use but there are a few modifications to power my Autometer gauges and a few other things. I'm considering using this as my excuse to rewire the whole truck, but for the time being if I can easily chase this down and defer the cost of the new harness that'd be my first choice.

Any advice on where to start?

The truck in question is a model year 1970 and here is a link to the wiring diagram: http://fordfuelinjection.com/files/Bronco_1970-71_02.gif

Unplug everything on that fuse and drive the vehicle just as before to see if it blows the fuse. Then one by one hook everything back up testing to see what system hooked up caused the fuse to blow. Curious, is the pigtail going to the trans. ground only? If it has power that pigtail swinging could cause a short. They sell small amp circuit breakers you could wire in for testing only to save from installing several fuses.