12 replies to this topic

[Jonny3979]

Good afternoon, (wiring by the way.......stupid me!)
I have a 1985 mayfair which I am trying to fit with a smiths electronic temperature gauge.

My question is (due to me loosing the fitting instructions....how do I wire it up.

I the gauge has 2 blade connectors - I assume one for ground/earth and one for the supply from the temp sender unit.
When I wire this up I get no reading at all. Looking on the www, it states that the sender unit is actaully the negative and I need a supply from the battery for the otherside???

Im confused over this, so I thought Id ask the experts.

Many Thanks

Jon

Edited by Jonny3979, 11 December 2009 - 01:21 PM.

[lrostoke]

you need an ignition switched 12v positive supply going to the gauge

the other blade does indeed go to the sender unit on the engine block. (just above alternator)

[dklawson]

Traditional Smiths gauges (made after the mid 1960s) do not connect directly to a +12V supply. The stabilizer provides the gauges with a regulated 10V DC supply. If you do not use the stabilizer the gauges will read "high" and you will shorten their life. Smiths gauges made after the mid-1960s are also not polarity sensitive.

One gauge terminal is connected to the "I" terminal of the voltage stabilizer. Where the stabilizer is varies from year to year but generally they are on the back of the speedometer. The other gauge terminal is connected to the sending unit (which provides the earth connection as you said). From memory, I believe the temperature sending unit wire is green/blue.

[Jonny3979]

Excellent,

Thanks

If I check the voltage at 'I' in the stabilizer at it isn't 10v then the stabilizer is probably faulty????

I shall go and dismantle my dashboard.........again!!!

JOn

[paul6266]

im sure you need to earth it out somewhere there iswell guys or is that just being being dumb?

[lrostoke]

I forgot about the stabilized positive feed

Only reason to earth the casing is if you are using the gauges with the illumination bulb which earth through the body.
No earth needed for the gauge to function .

[paul6266]

oh yeah thats a point no worrys i was just thinking about how i wired up the ones in my old mini but i did have it lit up

[dklawson]

If I check the voltage at 'I' in the stabilizer at it isn't 10v then the stabilizer is probably faulty????

Well... yes and no.

The voltage stabilizer is a sort of high-speed thermal switch. 12V goes into the stabilizer where contacts open and close rapidly in response to the internal heating of some components. The output of the stabilizer is an "AVERAGE" 10V. The problem is that the stabilizer output is not continuous, it switches rapidly between 0V and 12V. SOME analog volt meters (the ones with needles) may be able to show 10V. Digital multimeters sample a few times a second and may not be able to accurately display this average output of the voltage stabilizer.

If your fuel gauge is working and appears to be functioning properly, this is an indication that the voltage stabilizer is working properly and should be suitable for powering the gauge you are adding.

[Jonny3979]

Well, i tested the voltage with a digital meter and the I was putting out all kinds of results - between 0.5 and about 5 - never any higher and always irratic. I decided to take it out and clean the connectors - pushed it back in and now it does work as the fuel and temp gauge dont have a reading at all.
Ive bought a new one from flea bay so Ill puch that one in and see what happens

Cheers

Jon

[dklawson]

all kinds of results - between 0.5 and about 5 - never any higher and always irratic.

now it does work as the fuel and temp gauge dont have a reading at all.

The erratic jumping on your digital meter is more or less "normal". As I mentioned, those meters sample and update a few times a second so it's very difficult for them to capture the average voltage coming out of a Smiths stabilizer.

I assume in your other sentence you mean that you cleaned the connections and now neither gauge works. Did the fuel gauge work before?

[Jonny3979]

Doug,
Yes you are right and my rubbish grammer -

The fuel gauge used to work and so did the temp gauge - the fuel gauge was spot on, but on start up, my temp used to just go straight to the red, I wanted to wire in a smiths external gauge to double check the original temp - however I obviously had it wired in wrong.

JOn

[dklawson]

OK so both gauges used to work after a fashion. You said you have a replacement stabilizer on the way so there's no reason to worry much about this until the new part arrives.

Once the new stabilizer arrives and you've wired it up, first note that whether the fuel gauge behaves properly again. If it doesn't, something else in the wiring has problems OR you could have bought a defective stabilizer. Even brand new Smiths stabilizers can have problems... right out of the box. You can send a PM to Jupitus through this board. He was at one time making solid-state voltage regulators to replace the Smiths stabilizer.

Once you have the fuel gauge working properly again you will know that the stabilizer is functioning. At that point you can turn your attention back to the temperature gauge. You said it pegs on "hot" after a few moments. That is an indication that either the sending unit OR its wire has developed a short to earth. The test method is fairly easy. With the ignition on, remove the green/blue wire from the temperature sending unit. On pre-injected cars this will be on the cylinder head just below the thermostat housing. With the green/blue wire disconnected at the sender, the gauge should remain on COLD with the ignition switch in the run position. If instead the gauge goes to HOT with the wire disconnected, look for a short in the green/blue wire. If the gauge reads COLD and you then touch the electrical connector on the wire to an earthing point, the gauge should climb to HOT. If that happens, look for the fault to be in the sending unit.

[Jonny3979]

Many Thanks for the help Doug,

I got the stabilizer on flea bay froma place in Winchester - ordered at about 4pm, arrived next day - very impressed ( that's the second order 1st was H4 lights, they arrived next day too)

Anyway - withthe stabilizer fitted, I added a wire off the screw which sits where the I pin is and put that to the external temp guage, the other to the green and black wire from the temp sender and hey presto - 2 gauges working fine, a fuel guage which is fine and an engine which seems to run really well -tempwise.

Any Thanks

JOn

Now just need to swap that 998 unit for something a little bigger!!!!!