Fuse keeps blowing

[Raywoodhams]

The number 6 fuse (15A) in the rear fuse box keeps blowing. This means I loose rear light, brake light and horn, and also interestingly the power socket in the front storage box.
I thought I had traced the problem to a failed number plate bulb, which I replaced but the fuse just went again. Obviously this is pretty disabling. Any ideas?

[azgman]

i would suspect the glove box socket. If you have an ohmmeter you can disconnect the negative lead of the battery and start looking for a short or near short. A 15 amp fuse means at a nominal 14 volts from the charging system, you shoud have no less than .93 ohms to ground.

[john348]

Sounds to me like an intermittent short so put the meter on and hit and wobble things to see if you get a short?  You can sometimes telll fromt eh fuse if it was a short or just taking too much current over a long period.  IF you have a meter with a 'sounder' it would be a lot easier.

[Raywoodhams]

Thanks both.
I do have an ohmmeter but not much experience of using it, so forgive the dumb questions. where exactly should I be making the ohmmeter connections, And why disconnect the battery terminal?

[john348]

You want resistance from earth to fuse.  If you leave the battery on you run the risk of putting 12volts across the meter when in resistance mode which might do the meter damage depending on the meter.  So you can just pull the fuse and go to the non powered side (the side feeding the lights etc )and measure resistance but as said if you get it wrong you run the risk of damaging the meter so always best to disconnect the battery for safety sake especially if you are a bit unsure..  Some meters have a buzzer that sounds when you get around zero ohhm so you don't have to put the probes on and then look at the meter face whilst trying to wobble things (can get tricky)???  You just listen for the noise.  The way to test is to choose what you think is the right setting and then touch the probes together to see if it buzzes.


Hope this helps???

[Raywoodhams]

Right I have it, thanks.
I disconnected the negative battery terminal, put one of the ohmmeter wires (black) onto the disconnected wire, and (Red) into the fuse connector, with the fuse removed. I consistently got a high resistance 60 - 70 ohms, and this remained stable while I wiggled wires.
 I have run the ohmmeter over the rear light unit, a potential suspect, and there seems to be appropriate resistance between the ground connector ( I assume this is the black as it is the only one that goes to each of the light connectors) and each of the live feeds in turn.

 I wondered if there are any relays in the circuit which would affect the readings, or mean that sections of the wiring are missed from the test, for instance the lights don't come on unless the ignition is on and the engine running, which obviously can't happen with the battery disconnected.

[Coconut]

You want resistance from earth to fuse.

If I could add  "..... to indicate no fault."

Ordinarily there should be resistance between the fuse and earth ( or "Ground" )  i.e. an "Open" Circuit,
when any switches for that circuit are off.

When there is No ( or very little )  resistance, this indicates a fault,
as the current will pass straight to Earth and blow the fuse.

A meter equipped with a buzzer will sound when there is no Resistance,
so as John says, if you wobble the wiring loom /switches etc around,
and this makes the buzzer sound - it indicates where the wiring fault ( Short Circuit ) is 

Having said all of this, I've studied the Trophy SE wiring diagram and Service Manual,
and while it is not the simplest of diagrams to fathom out,
it seems that Fuse No.6 in the rear Fuse Box, does not protect the Accessory Socket in the Glove Box,
that is protected by a 10A fuse - which is Fuse No.2 in the Front Fuse Box,
so either the Wiring Diagram is wrong, or there is something more complicated going on with your wiring,
and I would recommend, esepcially during the Warranty period, to get it looked at by your Triumph Dealer 

[Raywoodhams]

Thanks Coconut, I thought it was a bit strange having the power socket on the same circuit. I have given up for today and will check the other fuses in the morning