[Shop-talk] Finding a Blown Fuse (Automotive)

[Eric Russell]

Oh wise & beneficent Shop Talkers - I've run into a situation that has me
stymied. I need help locating a blown fuse in a motorhome.

We recently bought a new (to us) motorhome. When installing the signal
booster for a TPMS (Tire Pressure Monitoring System) I accidentally shorted
a 12V wire in the cargo bay lights. There was a small spark (followed by a
few swear words). I then went on a hunt for the blown fuse. There are three
fuse panels in this motorhome. Two in the Ford chassis (F-53) - one under
the hood and the other inside near the parking brake - plus one in the
motorhome's 120V - 12V power converter. I could not find a blown fuse
anywhere.

I contacted the manufacturer (Thor) who has actually been quite responsive
& has tried to help. After asking for my vehicle's VIN they emailed me some
schematics (not actual wire diagrams but more a map showing the general
location of outlets, switches, etc with indications of which circuit they
belong to). There are two schematics that appear to apply to my motorhome -
one indicates the cargo lights are connected to the Ford panel by the
parking brake, another indicates they are in circuit #6 of the converter's
12V panel. Neither of those fuses are blown. While there I checked all the
fuses I could locate - none were blown. I've also signed up to a couple of
motorhome forums but have not been able to find an answer there.

Finally - my plea for help - is there any device one can use to trace where
a circuit originates? I've seen an electrician use a device to find out
what outlet goes to which breaker in our house.

I've followed the hot wire from the cargo bay light back to where it enters
a wire harness along the motorhome's frame rail. I'm loath to rip open the
wire harness trying to chase the wire further upstream. As far as I can
tell there is nothing else in this circuit - everything else is working
properly. Of course I can live without cargo bay lights but it bothers my
OCD to have it not working (when I know it did before my screw up).

-- 
Eric Russell
Mebane, NC
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