Keep Blowing tail light fuse

[roadsterdude]

1971 521.  After I git the truck I realized the headlight switch was previously repaired and shorting out.. Would blow fuse immediately.  I broke down and replaced the switch and the headlights are AOK now, but no tail lights/parking lights/side markers lic plate light etc an the first pull.  I keep blowing the fuse even with the new switch. I know there are a bunch of lights that work on that circuit so tracing everything to find a short is a pretty big deal, but ongoing.  I notice the way mine is wired that there is a wire going from the battery directly to the front of that fuse on the box (3rd from the left)  Is that the correct set-up?  Asking to see if there is a known issue with this circuit or do I just keep tracing wires in the harness.  Am I correct that the dash lights are also on this circuit?

 

[d.p]

Yes that is for 12v switched power IIRC:

 

 

When I first got my truck I kept blowing the water temp or gas gauge and it turned out to be the alternator.  I tried chasing all the wires and connections but in the end simply getting a new ALT fixed it.  

[datzenmike]

Front and rear running/parking lights, side marker or clearance lights, license plate light, dash lights are all on that one fuse.

 

Follow the harness on the frame under the box, forward and look for a plug connecting it through to the fuse box. Un plug and see if the fuse blows. If it does the problem is narrowed down to the rear tail lights. If no change unplug the front side marker and front amber parking lights and put a fuse in. If ok start plugging them in till it blows to find the one at fault. Good chance it's water in the bulb socket and corrosion. Seems unlikely it's the dash lights.

[banzai510(hainz)]

clean those fuse contacts where the fuse goes. try that first.

 

yes there is a Power wire from batter to the fuse box. that is NORMAL.

 

On my 521 the rear lamps was full of water but lucky is never pope the fuse... tHE SEAL WAS BAD AND WATER WAS HALFWAY UP. I just drilled the hole in the bottom for water to escape

 

if you tried everything else I would pull the instrument panel connector  just in case it is in there.

 

maybe there is a rusted or shorted out bulb. wire touching soemwhere. separate then try again.  But clean the fuse box copper contacts first

 

Edited February 23, 2021 by banzai510(hainz)

[roadsterdude]

Update:  Thanks everyone for your suggestions.  I finally traced it down.  After disconnecting connector to the rear (taillights/license plate light and rear side markers, the front parking lights would remain on with no fuse blown, so I started disconnecting one thing at a time and isolated it in the left rear tail light.  after thoroughly cleaning connections and applying some dielectric grease I have lights and no blown fuse any more.  Hate electrical gremlins!!