roy4matra
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« Reply #1 on: February 21, 2021, 03:15:43 pm » |
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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: Simon Auto and Carjoy now have new circuit & fuse boards that use the modern blade fuses, yet are a straight swap with no mods. needed. I have one of these in my stock if anyone wants one.
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 easily 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 positive 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 chassis 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. 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
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