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Author Topic: Murena Electrical Problems  (Read 1033 times)
roy4matra
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« on: February 21, 2021, 12:10:47 pm »

Unlike all modern cars with multiple networked computers, which has made them extremely complex, the Murena has a very simple electrical system, and the wiring diagram barely fills half an A3 sheet of paper!  It can be easily fitted on to the two sides of an A4 sheet, which is what I do for my laminated wiring diagrams.

The first thing you should understand is that there are many copies on the internet of inaccurate Murena wiring diagrams partly because an original factory one had a few mistakes in it, and subsequently someone inaccurately copied this but unfortunately added some more errors.  Therefore many of these diagrams have as many as 25 or more faults!  There are also mistakes in the Murena hand books so you must be aware of those too.

I have had my Murena from new and been a technician for over 45 years and have dealt with virtually all the systems from the early very simple pre-war vehicles to the very latest highly complex computerised ones, and therefore understand them.  When I realised there were mistakes made in the Murena diagrams, I set out to correct them all.  Also Matra only ever issued one diagram for a 1.6 and another for a 2.2 model, but in fact those two are insufficient since there are a number of variations in the models, during the relatively short 3 year plus production.

Consequently, I have available the correct, accurate, diagrams for any model produced, and only need to know exactly what you have, and I can provide a diagram to suit.  Please contact me on my domain email (roy@matraclub.org.uk) to request one.

If you do a topic search on this forum specifically for Murena wiring diagrams, you will find something like 35 entries, from the early days to the present and although the poster has tried to be helpful, in many of these there are mistakes or assumptions, or they have used one of those inaccurate diagrams, or they have not understood that there are differences with some models so they may have an early car but are trying to advise someone with a late car, or vice versa, and that can lead to mistakes.

To give you two examples, the early Murena 1.6, like the Bagheera, had the instrument panel illumination come on with the ignition, so it is always lit up when driving whether you have the external lights on or not.  This was the reason for the green 'Lights on' warning light in the instrument panel.  Since the dash is lit all the time, it does not indicate that you have your side lamps switched on.  When you did switch them on, this warning light would come on and indicate that you had them switched on.  On the later Murena, and any conventional car, you really don't need that green warning light as the dash illumination comes on with the side lamps and is sufficiently bright to warn you that you have switched your lamps on.

Again on the early Murena since they used the same instrument panel as the late Bagheera, there was one warning light to indicate low or no vacuum, generally indicating a leak in the head lamp raise/lower vacuum system.  The Bagheera had a vacuum sensor in the front compartment that triggered that warning light.  However, as far as I am aware the Murena was never fitted with that sensor, so that warning light was never used.  On later Murena they replaced that unused red warning light with an orange choke warning light and the switch for that was fitted just behind the choke knob in the compartment under the gear lever surround.  It is a shame they dropped the low vacuum warning light as it is vital that you cure any leak in the vacuum system quickly, because a leak here will cause a weak fuel mixture and probable subsequent engine damage.  DO NOT ignore a vacuum leak.

These two examples show why there are differences necessary in the wiring diagrams.  There are others such as the diagnostic socket on early cars having 12-sockets (3x4 arrangement) with pins in 11 of them; later 2.2 cars having only 6 pins in them; or later 1.6 cars having a 10-socket diagnostic socket (2x5 arrangement) with 8 having connections in them.  There are at least six different engine wiring looms; two different front bumper looms, two different main centre section looms; and three different rear lamp looms, so how can just one wiring diagram for a 1.6 and one for a 2.2 be correct?  They simply cannot!  Hence my diagrams are made to suit your car and each one I produce has the chassis number or VIN printed in it to show the vehicle for which it was produced.

As stated above, please contact me if you want a diagram for your Murena, and you will know that it is accurate providing your car is still standard.  If it has been modified by a previous owner, or you yourself have changed something, I could incorporate the changes if you wish but you would have to provide an accurate diagram of the changes.  This also reminds me to say that anyone who makes any changes to a vehicles wiring, on any vehicle, should always document those changes at the time, as you would be surprised how, many years later, you will have forgotten what you did; or these will help a subsequent owner understand the changes.  Always keep them with the hand books in the car in case they are need when out on the road.

As there are a number of recent owners who have bought Murena that have possibly been abandoned for years and need restoration, and they are therefore new to the Murena, I am also writing a second topic (to appear soon) about the common electrical problems, causes and cures, to collect them in one place to make it easier and save you asking the same questions asked many times in the past by other owners.  I hope you will find these useful.

Roy
« Last Edit: July 07, 2021, 06:12:25 pm by roy4matra » Logged

roy4matra
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« Reply #1 on: February 21, 2021, 03:15:43 pm »

Fuse board & terminals

I'll start at the fuse board since this is an essential item and is susceptible to a range of faults which can effect many other things.

The first thing to check are the fuses and how tight or loose they are between the holders.  These continental type fuses were never very good in my opinion when compared to the English glass fuses and when the holders at the ends become splayed out slightly, the fuse becomes loose and it is not unknown for the ends of the fuses to arc and burn away, such that the strip across the fuse may look fine, but actually the contact at the ends has become poor or even ceased to exist, which is the same as a blown fuse.  So if you have any fuses that are loose, remove them and check the ends.  Next you should gently bring the holders back closer together so that when the fuse is back in place, they are tight to make good positive contact.  Alternatively I have replaced the continental fuses with glass fuses with far more positive results.  Contact me if you wish to know more.

Next make sure the fuses are all the correct rating as many of the original ones fitted were actually the wrong colour for the respective ratings.  The board should have five 16 amp fuses (red) and one 8 amp fuse (white).  However, I have seen many incorrect white 16 amp fuses in these boards, so make sure the ratings are correct and do not go purely by the colour of the fuses.  If you have a Murena hand book, please note that the picture on page 53 is displayed with the fuse board around the wrong way with the fuses towards the front of the car (LH side in the picture) and the relays to the rear of the car (RH side in picture).  They are in fact the other way round, so the fuse numbers 1 to 6 are also the opposite way with No.1 nearest the LH edge of the car and No.6 (the 8A one for the side lamps) nearest the centre of the car.

Update June 2021: Carjoy now have a new circuit and fuse board that uses the modern blade fuses yet is a straight swap with no mods. needed.

The relays, although on the underside of the board, have all their terminals accessible on the top, so they are easily positioned to be able to check them without removing the board!  With the board correctly in the car (not that incorrect picture) the single relay in the centre at the back is for the dipped beam head lamps.  The other three relays in a row towards the front of the car are (from inner edge to the outside of the car) driving lamps relay, main beam relay and electric windows relay.

There are three diodes on the board which are for the circuits to operate the head lamp vacuum valve to lift and lower the head lamp pods.  If one of these fails so it will pass current either way, you can get the dip and main beam on together!  The diodes were never available separately but you could repair the board if you obtained some diodes from an electrical specialist.

Crucially, the edge connector terminals in the four plugs to the board are known to crack or break across the 'U' bend at the end, and thus lose contact with the board contact patches. (see photo)  When they crack and the contact becomes poor, you get arcing and burning which degrades the contact even further, and various things start to become erratic or intermittent.  Once they break altogether you loose the circuit and whatever it was controlling fails.  So if when you take a board out to check it, and maybe find burnt contact patches, also check the corresponding terminals in the plugs as these will usually need replacing too.  The problem now is that it is becoming difficult to obtain those edge connector terminals, so one alternative is to modify the board edge connection type if the rest of the board is still good.  Please contact me if you need this modification as it is too much to go into detail here.

Please be aware that if you have a German spec. Murena, there are two additional in-line fuses for the side lamps, one behind each rear lamp assembly.  This was to meet the German lighting laws.  So if you have one rear side lamp not working and the bulb seems fine, then it may be the fuse behind the lamp has failed.  Early cars had an in-line continental fuse, but late cars ('83) had a modern in-line blade fuse holder and fuse.

Earthing and connections

As all the Murena were galvanised totally by immersion into a hot tank of zinc, this procedure leaves a surface coating that can creep back slowly to cover say a scratch which is very useful for chassis protection, but it has a habit of degrading the earth points on  the car, of which there are many.  Earthing is as important as the feed if something is to work, so don't ignore the possibility that the earthing point might need cleaning back to bare metal.  One common fault can be the driving lamps not functioning.  They have a feed wire to them but rely on the mounting bracket making a good earth to the chassis at the point where they are bolted.  Therefore if the lamp has a good feed, and the bulb seems fine, it may simply be that the contact point of the bracket to chassis needs cleaning first and the bracket bolting back securely.

The other earth I've found needs cleaning occasionally, is the one on the inside of the RH strut tower near the ignition coil or amplifier.  You will see the black wires from the engine loom coming across to the chassis for the engine electrics earth.  Also underneath is the main earth braid strap from the powertrain to the chassis.  This is bolted to one of the differential casing studs and the tower for the gear change linkage.  Make sure that is good.

One important connection that sometimes causes problems is the main live feed from the battery to the circuit board.  A few inches away from the positive battery connection you will see a large red wire split away from the main positive cable that goes all the way down the chassis to the starter motor at the rear.  This red wire provides all the power to the circuit board, so without it you have nothing.  This large red wire has a large Lucar type male and female connection, the terminals encased in white rubber insulators.  I have seen these with such a loose connection that the resistance across the joint is high and the connector gets quite warm or hot to the touch.  Any like this will cause multiple problems, so please make sure this is a good tight connection and there is no heat there.

The original battery terminals on the main positive and earth cables can be poor and even when the bolts are tight, the terminals are not tight on the battery posts.  This is because there is no gap left to allow the terminal to close up any further on the post.  It is best to replace any terminals like this, as they are difficult to repair once they have got this bad.

Since most of the Murena wiring loom connection blocks are open to the elements, the connections can deteriorate and corrode, so if you have a problem on a particular circuit, check all the connectors on that circuit too.  A common failure was the large red (live) feed wire to the heated rear window relay which used to corrode badly in the connector near the windscreen washer bottle.  This is the yellow connector CC2 in the wiring diagram and is it pin 5 circuit 3C.  Often all that would be left was a load of green corrosion!  Therefore if you have no voltage at the heated rear window relay (on the RH side of the engine compartment bulkhead) socket pin 3, check that CC2 connector at the front.

Dashboard warning lights

There are 7 warning lights in a row at the bottom of the instrument panel, and another 4 above the clock.  The ones in the instrument panel, as stated previously in another thread, are (from left to right) Side lamps, Hazard lamps, Main beam lamps,  Low fuel, Fluid or Pads low, Low vacuum or Choke, and Charging lamp.  These are capless bulbs pushed into a holder which clips into the panel at the back.  The bulb holder should make contact at the top and bottom with the copper contacts of the circuit membrane but these contacts can get broken of bent back under the membrane so the bulb holder can't make contact.  So if the holder and bulb are good, you need to check the copper contacts from the membrane.  You will need the panel out to do this and whilst out you can check all the other contacts as well.  The main panel plug has a set of contacts too and any one of those can get broken or folded back under the membrane instead of hanging over the edge to be trapped by the plug to make contact with the plug terminals.

Sometimes the membrane can have a tiny break in a circuit which ends the circuit at that point and anything else that was supposed to be supplied will no longer work.  For instance, all four of the minor gauges are supplied 12v by one connection on the membrane, the leftmost gauge is the voltmeter, then there is the oil pressure gauge, the coolant temperature gauge and finally the fuel gauge on the right hand end.  On one car there was a micro-break between the oil and temp. gauges, so the temp. and fuel gauges were not getting any 12v supply and couldn't work.  This was simple to cure since each gauge is bolted in to the panel using the electrical contact points, so a small wire with eyelets at each end was made to be bolted under the mounting nuts and provide a bridging circuit past the break.

Continued in part 2.

Roy
« Last Edit: June 28, 2021, 11:06:50 pm by roy4matra » Logged

roy4matra
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« Reply #2 on: February 22, 2021, 07:41:23 pm »

Continued from part 1.

A point here about the Low fluid or Low pad material warning light.  This is simply a warning light that is lit when either the brake fluid drops below a certain point, or when the one front or one rear pad gets low and the contact touches the disc and earths.  It can also be activated by the centre button in the vertical row of 5 push button switches on the left.  This is a test function so you can check the 12v supply, bulb and earth are good.  Since it is simply a bulb lit by making an earth on a sensor, this can also be used for a low coolant sensor in the header tank.  This is a really simple modification I recommend.   It will give you an early warning that the cooling system is losing coolant, and long before that loss can result in any damage.  You fit a coolant level sensor in the header tank, then connect it on the car to the circuit and warning light that are already there.

The Voltmeter is a short scale damped instrument and doesn't always read true, so if you really want to check if your system is charging properly, then you should connect a proper voltmeter across the battery terminals and see what voltage is getting to the battery.  The test should be to bring the revs up to say 2,000 rpm and the voltage should be between 13.4 and 14.4 volts.  Then switch the head lights on, and check it stays in that range.  As the head lights load the system the voltage may drop for a fraction and then the alternator should increase its output to keep the voltage in the correct charging range.  Anything under 13.4 means it is not charging; and anything over 14.4 means it is overcharging, which can heat up the battery and boil away the fluid. (and even in extremes buckle the plates inside)

The reason the instrument gauge often reads low, is that there are numerous contact points along the circuit and unless they are all good, you lose some of the voltage such that the gauge is not getting the true reading.  I have measured the voltage at the back of the gauge on some cars and it has been 2 volts lower than true!  Since this is a short scale instrument, that only reads between about 10 and 18 volts, if the car is charging at 13.4 volts but the gauge is only getting 11.4 volts, you can see that it will be almost at the bottom of its reading scale.  This is often why the needle hardly moves up.  However, I can assure you that since I have had my car from new, I know that it originally read correctly in the centre when the circuit contacts were all good, and if all the connections are cleaned and if necessary re-tensioned, a low gauge reading needle will return to the centre area.

Roy
« Last Edit: July 07, 2021, 06:29:42 pm by roy4matra » Logged

Murenanimal
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« Reply #3 on: March 02, 2021, 08:04:33 pm »

Great exposÚ! Really true.
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