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Author Topic: Fuse board connections  (Read 122 times)
roy4matra
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« on: February 27, 2019, 03:47:51 pm »

As most Murena owners will know by now, there are a few weak points with the fuse board and the terminals in the plugs that slide on to the edges of it.  First the contact patches are only on one side of the board, so although the terminals in the plugs could have contacted both sides and doubled the contact area, we actually only have the lower side making contact.

Now the terminals are shaped to give them a spring action against the contact patches, but these terminals crack and break across the end of the 'u' bend that gives them the spring action.  As they crack, the pressure against the contact patch is reduced and arcing starts, eventually burning the contact patch, further reducing the contact.  So the first thing you need to repair the plugs are new terminals to fit in them, but these are now becoming very difficult if not impossible to obtain.

The board tracks sometimes become broken or burnt through, usually through a short or overload, which you might be able to repair, but sometimes you really need a new board.  These boards use the old style continental fuses which are simply a shaped piece of plastic with a wire wrapped from one end to the other.  They were cheap but never good quality and thankfully they have now been replaced by the blade type fuse!  One quirk with the continental fuse is that if the pressure on the ends was poor, it is known that the end can burn a hole in the middle of the metal leaving no connection with the fuse end holders, so although the wire across looks good, the fuse is not actually transmitting from one end to the other!  Re-tensioning the ends plus a new fuse will cure this until the ends get slack again and starts the burning again.

If you need a new fuse board because you have burnt contact patches, burnt out tracks, poor fuse holders, or a combination of any of those faults, the problem is they are no longer available.  Simon Auto and Carjoy had a small number of new copies made which were better quality than the originals, but these are now all sold.

So what do you do if you want to keep the car looking standard, don't wish to make major modifications to the wiring circuits, and need a new board or new terminals or both and cannot get them?  One solution I have come up with is to repair the existing board if it is not too far gone, and replace the edge plugs and contacts with a better design.  You have to drill tiny holes in the board for the terminal headers, which are then soldered to the board contact patches.  You next remove all the edge terminals from the plugs and cut off the terminals.  The wires are now tinned and fitted into some small plugs (with screw connections) that mate with the terminal headers.  Once these are plugged in, the system will work just as before but probably more reliably as you are no longer relying on sprung edge connectors.

I am attaching a photo of one of my boards that I've used for trialing various solutions, so you can see and hopefully understand what I have achieved.  (please ignore the glass fuse modification - this is another trial I have been doing to get rid of the horrible continental fuses!  The old English glass fuses provide better positive end connections!)

I have used some *Maplin supplied terminal headers but their matching plugs were too high to allow the board to clip back in to the surround, so the low-height plugs necessary have come from a company in the Far East! (where there always seems to be someone who has just what you need)  I can either supply the parts as I bought some extras, or I can supply the company details if you prefer to buy them directly yourself.

Roy
*Correction, the headers weren't Camden Boss they were from Maplin, but they no longer exist!  However the company that supplied the low-height plugs also do similar headers.
« Last Edit: February 28, 2019, 06:34:00 pm by roy4matra » Logged

murramor
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« Reply #1 on: February 28, 2019, 08:36:30 am »

Those look really neat, Roy.
Ron
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Ron Murrell
Sydney, Australia
Anders Dinsen
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« Reply #2 on: March 17, 2019, 12:38:02 pm »

Indeed, that looks very good and is definitely worth considering. Thanks for sharing this, Roy!

/Anders
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'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
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