Morris Minor Owners Club

OK folks.
How do I wire up a standard Lucas +30/-30 ammeter?
It has lucar connections on the back, two big ones and two small ones.
Thanks

Hello Jo,
I'm assuming a dynamo and positive earth; battery positive disconnected, disconnect the brown wire at the solenoid that runs from the 'D' terminal on the voltage regulator. This now goes to one side of the ammeter into the large Lucar connector, from the other Lucar connector continue back to the original solenoid connection. Either remove, if possible, or insulate the smaller Lucar connectors as they are not needed. I.e. the ammeter is in series with the 'D' to solenoid connection. Use equivelant size cable and ideally the colours should be brown\white to the ammeter and brown from it. Pay particular attention to the crimping and ideally use the totally insulated crimps as a short to earth will be severe.

Alec.

P.S. swop ammeter connections if it shows a charge when you first switch on.

Cheers Alec.
Very clear and precise. Because it measures current, I knew I had to break into a cct.
I WAS tempted to stick it across the battery to test it (like a volt-meter), but decided against it!

Hello Jojax,

just as well you didn't as that would be a short circuit, very hazardous indeed. Ammeters and Voltmeters may look similar but they are completely different in characteristic. Ammeters are very low resistance and voltmeters are very high resistance. It may seem confusing as a multi meter uses one instrument for both functions but that is with integral circuitry.

Alec

It may seem confusing as a multi meter uses one instrument for both functions but that is with integral circuitry.

The multimeter usually has seperate connector!

Hello Ray,

yes, but it still is the same meter. What I was getting at is that it could be confusing, I would guess that the average DIY'er has little need to use the current ranges and indeed may not be aware of the correct method of connection.

Alec

Personally I've never once had to measure current. You need to break into the cct. at some point to do so. Much easier to measure potential difference (voltage) between 2 points.
Could always use the old Ohm's law to calculate current, given voltage and known resistance. My multimeter gets used simply for continuity tests on 9 out of 10 situations.............
I've not had much success in wiring my gauges thus far. Even the temp gauge goes way off the scale, although the engine is clearly not overheating. Hmmm.............. a new sender is required, methinks!

Hello Jojax,

yes, that is what generally they are used for. Ohm's law is fine if you know the resistance, but if you want to check a motor current, the load is a factor there.
have you got a voltage stabiliser for the temperature gauge?, the Smiths instruments use a regulator which is used to supply the instrument with a stabilised 10 volt supply. Disconnect the sensor cable and it should read zero and earth it, it should read full scale.

Alec

Much easier to measure potential difference (voltage) between 2 points

Occasionally that gives a wrong result. If there is a high resistance circuit you will see 12v with a meter (as it draws almost no current) but connect the equipment back up and it won't work as the current flowing creates a huge volt drop in the wiring loom.
Therefore a bulb attached to long wires - one with a crocodile clip and the other with a nail on the end can be a more reliable thing for fault diagnosis.
As mentioned very correctly by Alec - Ohms law is only useful when you know the resistance so the resistance of the supply circuit is one of the most important things for any equipment that used a high current. I remember working on a motor that drew up to 10 amps. Even with a 14 volt supply, the motor only saw 10 volts under load as the wiring loom was not ideal.

Jojax remember there is a voltage stabiliser on the back of the speedo head that you can use.

Hi Alec,
No. I never knew anything about a voltage stabiliser. I've simply connected one side of the gauge to switched power, and the other side to the sender on the cyl. head.

Hello Jojax,

that won't help you, as Kevin points out there is one installed. Take a feed from that and see how you get on (or from the fuel gauge which is what the stabiliser is currently (sorry) feeding. (LIGHT green cable))

Alec

OK............next question. How do you get access to the back of the speedo?
I've taken out the driver's side glovebox, but that only gives limited access............

It's a struggle, but there's a machine screw either side that you can reach through the gloveboxes. Loosen and the speedo comes free. Crick your neck and swear a lot and it's not *too* hard.

OK.
If I have problems (and I probably will!) can I just buy one of these voltage stabilisers and fix it (earth it) to the bulkhead?
I suppose I could just wire it to the fusebox, and inside to the temp gauge?

OK guys,
Got this stablizer thingy.
noticed that the two terminals on the left are female, and the two on the right are male.
Where do I connect the +12, and the feed to the temp. gauge?
Thanks!