Any Fuse-Blowing Diagnostic Tricks?

[gwbutler]

Hello all,

My 84 4ksq has been entertaining an electrical gremlin for a very long time.  I've made numerous attempts to get to the bottom of the problem and each shot at it makes the problem more perplexing.  I'm hoping that a lister has resolved the indentical issue.  

The problem is that the car keeps blowing the S17 fuse (supports the blower, radio, antennae, cigar lighter, glove box light, etc).  What makes the problem complex is that the car doesn't blow the fuse consistently.  I have gone months without blowing the fuse, only to hit a period (like now) where the fuse blows everytime I use the car...but not always immediately!

Case in point: A few mornings ago I; replaced the fuse, started the car, turned on the blower (to position "2"), drove toward work for approximately 15 minutes, turned on the radio...and everything was fine all the way to work.  After work I; started the car, (blower sitch was still in the "2" position) the blower worked, turned on the radio after only two minutes this time, and the blower died (blown S17)! Sometimes the fuse blows the second it is placed in the holder...even with the car off.

To date I have:

. placed an in-line fuse on the "hot" wire to the power antennae (BTW, the antennae is a Blau-provided OEM replacement...and the problem didn't exist prior to replacement...fuse still blows with antennae completely disconnected)

. removed/disconnected every device on the circuit and STILL blown the fuse...really!

. replaced the blower control switch (with one from my old 84 4ksq cannibalization unit)

. replaced the enormous resistor supplying the blower speed selection at the blower motor (used unit...same symptom)

Does anyone have any clever diagnostic "tricks" that they use to specifically isolate intermittent shorts...or intermittent over-currents?  I'm pulling my hair out on this one.  Any suggestions? TIA

Regards,

George B. 
Massachusetts