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

[Pat Horne]

Yes, cable tracers are very handy, I have 4 of them in one form or another. I’ve found that there are two classes of tracers, cheap & not so cheap. Units under about $50 will work for most jobs, but the more expensive ones generally have greater sensitivity. 2 of mine are cheap, one is Fluke & one is part of a high dollar instrument for actually measuring the specifications of cables. 

One helpful way to increase the sensitivity of the tracer when tracing a pair of wired is to connect the signal generator to one of the conductors & the other test lead to ground rather than to both of the wires in the pair. 
This also helps when you have a short between the wires you are tracing. 

None of them work for finding cables in buried PVC conduit, even when right against the conduit. 

Fluke & Greenlee seem to be the best bang for the buck if you are going to use more than a few times. 

Peace,
Pat

Pat Horne 
We support Habitat for Humanity


On Nov 12, 2021, at 12:24 PM, Brian Kemp <bk13 at earthlink.net> wrote:

 Saw this problem was solved, but wanted to add my feedback on a cable tracker that others have mentioned.  I have a 5+ year old version from Harbor Freight, but it is no longer on their site.    This appears to be the current version:

https://www.harborfreight.com/cable-tracker-94181.html

I was doing some renovations and had wires in electrical outlook boxes that I couldn't identify.  With the power off, I connected the signal generator and was able to trace the signal with the wand through the plaster walls.  Both went to locations in the wall with no exposed box - bad work by someone decades ago.  The plaster walls were a challenge and I only got a weak signal, but was able to know it was ok to cap the wires.

I also have about 10 phone jacks in my house, with some shorts in some of them.  The phone company installer initially just disconnected everything and reconnected only the two I was going to connect.  A few years later, I needed to move my DSL modem, so needed to activate a different jack.  Connected the signal generator and ran the wand over the disconnected wires at the central phone termination to find the one I needed to connect.

Brian

On 11/10/2021 4:15 PM, Eric Russell wrote:
> 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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