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Author Topic: Murena Electrical Problems (part 2)  (Read 54 times)
roy4matra
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« 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 simply modification I recommend, to give you an early warning that the cooling system is losing coolant, and long before it can do any damage.  And it is simple to connect a new coolant level sensor on the car as the circuit and warning light 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: February 23, 2021, 05:16:06 pm by roy4matra » Logged

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