Why did my fuse box melt?

[totorro]

Coming home earlier in the week I noticed my right hand headlight was out. Side light and main bean still working, just no dipped beam. I had a look the next day and swapped the bulbs to test them, both bulbs were fine. A voltage reading was fine until the bulb was connected when it dropped, which suggested a dodgy connection. The connector for the bulb was a little cracked and the spade connector pretty manky - I was putting in a Brickwerks order for some other things so ordered some new ones as well.

Swapped over the connector today but no improvement. I then checked the other end at the fuse box and found a molten mess. In hindsight I should have had a look there first!





So happened here? Was it a bad fuse which didn't blow when it was supposed to? Bad connection / rust / debris in the fuse box? Anyone had this happen before?

I remembered that the previous week there'd been a smell of burning plastic when I left the house, it didn't seem to come from anywhere specific, there was no smoke and it passed, so I'd put it down as coming from somewhere outside...

Wiring is as factory as far as I know and can see, no relay mods added. One thing I wasn't sure about is that I have 2 wires coming out of the "M" connector on the back of the CE1, one white and one yellow. Bentley shows these as connected to the lighting, but lists them as open, so where do those wires go? They look factory.

Longer term I'll need to replace the CE1, but shorter term I'll need to cut some wires and route around it via a separate fuse. I guess the questions are; should I also do the left hand side, and should I do a relay mod while I'm there?

[Mocki]

Cheap nasty fuse ? Often really cheap fuses dont blow when they should , but 
Generally dirty ,loose , bad connections get hot , which makes them dirty , loose worse connections and the cycle only gets worse , hotter looser , melted . 

 you could have a chaffing issue on the wire elsewhere ?

 

[totorro]

Cheap fuse is a possiblity, it's different to the others so has been changed in the past (but not by me). Surprised it's melted so much but still hasn't blown.

Going to check the routing of the loom for any issues as best I can with the dash in place.

Plan for today is to to put a relay on the feed from the dash, with an extra connection via a new fuse and then connect to the lighting loom. Going to leave the LHS as it is, but it'll at least get the benefit of the relay. Means once I replace the CE1 there'll just be one extra connection in there.

[cobblers]

See this from time to time.
Dodgy chinese "fuses" can cause it, or a tarnished/corroded connection.

Either way, I'd recommend replacing the whole fuse box rather than bypassing that single circuit. They're not expensive and it's actually a fairly straightforward job. The one on my Doka was melted similarly - A good used CE1 was about £40 and it took about 30 minutes to swap. AFAIK all the CE1 fuse boxes are identical.

[BarnyE]

A bad connection between the firebox and fuse meant the connection overheated, so fuse won’t blow as ampage through the fuse is normal. But resistance in the connection causes it to melt.


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[totorro]

I've wired in a external fuse and relay to get it working again for now - as I'll need to drive this week.

A good used CE1 was about £40 and it took about 30 minutes to swap. AFAIK all the CE1 fuse boxes are identical.

There's a few on eBay but they're at the £60-70 mark - have posted up a wanted ad.

A replacement will be a good opportunity to clean all the connectors as well as get in and clean the earths while it's out.

I'm still none the wiser on the M1 / M2 connections and where they go? Could these be a UK spec extra related to the appropriate side light coming on when the indicator is left activated with the engine off? Don't see anything on the Bentley diagram which looks like it'd do that.

[Robsey]

All the fuse box connections are listed here...

viewtopic.php?t=173773

It starts at the "G" pins first...
But keep reading on, and you will come to the "M" pins later.

[totorro]

Loads of good info there

For the M pins it has

Connector M

Not normally externally connected.

M1 INTERNAL grey yellow to pins A9 and G7
M2 INTERNAL yellow to pin A21

Where would they connect externally... when I get the fusebox out I might have better sight of where they go.

[Robsey]

External Connections are as Listed.

So for M1, it is internally linked to A9, and G7
Which is externally connected as follows:-

A9 WHITE / BLACK LIGHT SWITCH CONTACT 56 feed to stalk dip/high switch and pins G7 and M1

Pin G7
56 Voltage rail. (Feed to head lamp circuit).
Internal connections to:-
A9 - White / Black wire from light switch pin 56, and also to the dip / high beam stalk pin 56.
M1 - not used.

_____________
And for
M2, it is connected internally to A21

A21 YELLOW LOW BEAM CONTACT 56B headlight flasher switch and pin M2