Voltage Stabiliser
 

My temperature and fuel gauges do not work at all and I see in the wiring diagrams a voltage stabiliser.

Is anyone able to explain exactly what it is please?

I wonder if I’m able to get an alternative. Is it 5V or something?

They are usually 10v out for varying voltages in. Gives the instruments stable voltages and so give a correct measurement. For the 142 it's probably a small rectangular relay type of can and is normally fitted close to the instruments. Check your fuses. Amazons sometimes lose their small gauges if one of the fuses is bad or making bad contact.

Thank you Derek.

My plan is to get in behind with my voltmeter to check there's good feed to the little can. A bit of research suggests while 240's are 10v, the old 140's are 5.1V and as such, the can can be replaced or repaired using a 5v voltage stabilizer.

To check the gauges, I wonder if I can use my Tomtom plug which is 5V?!

Yes, for the older 140s, this "stabilizer" would be "5.1volts". Now, I'm no electrical genius and could be completely wrong, but I tried to do what I think you are wanting to do by building a 5.1v stabilizer with modern components. It didn't work. I believe that's because the way the original one works is not by putting out a continuous 5.1 volts. Instead, it constantly cycles on and off. When on, it's actually passing the full 12 volts. If this was allowed to constantly happen, that 12 volts would burn out these gauges. That's why it continually cycles back off and is only on for a very short amount of time. Because the gauges are 'slow' and don't react instantaneously to the loss of voltage, you don't see any effect, as long as it cycles back on quickly enough.

Basically, this stabilizer provides an AVERAGE of 5.1 volts, not a constant 5.1 volts. I suspect the reason a modern 5.1 volt stabilizer doesn't work is because the gauges need 12 volts to show anything, even though this voltage would quickly burn them out if provided constantly.

You may need to buy am instrument cluster with a known good stabilizer that you could scavenge in order to get a replacement.

Yes, it is 5.1v which surprised me. Attached a page from the electrics Green Book. Stabilser is shown in pic at left top, the rectangular can with the wires going to it.