Signum mirror not dimming (again)

It's gone again - last time it was a fuse, but since I didn't change it, and
it is not mentioned in the manual, I was wondering which fuse it is. I
pulled a few out, but did not find a blown one. A few would not come out,
so I would like to know if it is one of these before I put any major effort
into removing it.

Bob

 

7.5 amp fuse in the fuse box in the boot - fuse number 27

 

I will look tomorrow - the manual says fuse 27 is a 5A for the AC which is
working ATM. Does it make any difference that it is a '53 2.0 DTI Signum?
Fuse 28 is 7.5A, but again, I am sure the things listed in the manual are
working.

Bob

 

The wiring diagram says it is fuse 27 in the fuse box in the boot but they
have been wrong before. If you can get to the mirror multi plug see if you
have a 12v ignition feed to terminal 1.

 

Thanks, it was fuse 27 in the boot. Both the manual and actual fuse were
5A. Replaced with a 5A, and everything is fine. If it blows again, should
I put a 7.5A in?

Bob

 

No!
Find out why it's blowing.
Dave

 

My thought is because they underspecced the fuse, since the current
schematics say a 7.5A lives in slot 27 (but you snipped that bit). It went
the first time after I had it 18 months, then a second time 3 months later.
If it blew as soon as I replaced it I would think something was wrong.

Bob

 

The thing is that it blew. You need to find out why. If the correct
answer is that the fuse should be 7.5A then by all means fit the correct
fuse. If the fuse is blowing because of a fault in the dipping mirror or
any other item connected to the fuse then (obviously) it needs to be
repaired. The last thing you want is to discover that the fault causes a
fire rather than just blowing a fuse to a relitavly unimportant (but
handy) item.

Sorry if it come over as "grandma and suck eggs" but the last thing I
would want to see anybody loose their car (or worse) because of an
aviodable fault.

I've just checked the fuses in the boot of my Signum (04, 2.2DTi). Fuse
27 is a 5A fuse. The manual says that fuse 27 is 7.5A and supplies the
seat occupancy system(?), tyre pressure system, rain sensor and air
con system. Plenty of scope there to look for faults! Any of those stop
working if the fuse is out?

You could try measuring the actual current consumption and monitor what
happens when each item is used. If a 5A fuse is fitted then I would
expect the current to be about 3A or so. If everything is working OK and
the current is 5A then perhaps a 7.5A fuse should be fitted. Remember
that these automotive fuses are slow blow fuses and intended to protect
the wiring not so much the item connected to the fuse.
See the link for the time current graphs.

http://www.cooperbussmann.com/pdf/4fbe87c5-af91-48b3-92e9-678115bcb53e.pdf

Waggle various wires, connectors etc to see if the current consumption
suddenly jumps. Look for trapped of chaffing wire (particularly if there
are any signs of bodywork repair). Put a 10A fuse in series with the
meter when doing this - just in case!
Dave