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Guest 2Bbuilt

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Guest 2Bbuilt

I have a 1988 gauge set, this is the type without rev counter

 

i am swapping it for a one for a MK2 with the rev counter and 2 smaller guages (fuel and temp) in centre

 

for a start the wiring is different colours and plug different. however i have a plug for the mk2 with wires

 

i can find wiring diagram for mk2 gauge but not for the earlier type

 

i do have all working except the handbrake and brake test light.

 

i have 2 wire left from old loom, one of which goes to centre wire of the brake test.

 

on the "new" plug i have 3 wires (2 are for the brake light, they have no power) plus my oil switch wire in the plug has 2 wires, 1 is connected to the oil switch but the other has 12v.

 

if i connect the 12v to one of the brake light wires it lights up, some bulb works.

 

i have connect the 1 and 2 wires for the handbrake light, nothing happening

 

can anyone help

 

a wiring diagram for the old gauge set would help as it is wired differently

Edited by 2Bbuilt
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if the clocks are working as in temp gauge etc then the clocks are getting the live feed they need

i had the same prob as the clocks were fauty so wired the oil light separate not bothered about h/brake light

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You will have +12 volts on either side of the h/brake lamp when it is off.

 

The h/brake is a switch to ground and THEN you will have 0 volts on one side of the lamp (and it will be lit)

 

I hesitate to question the master :) but are you sure ? Won't you have +12V on one side of the bulb and 'indeterminate' on the other ? If you had a +12V on the handbrake side of the bulb and then the handbrake switch earthed it you would short the battery ?

 

Thinking on, with the fact that the switch side of the bulb is not connected, does that mean the +12V is picked up 'across' the bulb ?

Edited by alanrichey
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To answer the question posed by Alan above.

 

If you attach one side of a lamp to battery +ve (12 volts) and measured the unconnected side to the battery -ve (0 volts) with a multimeter set to volts, you will find that there is +12 volts there.

 

The reason is that the volt or multi meter is a very high resistance instrument and draws almost zero amps. (The lamp will also not light up) Once you connect the other side of a lamp to the battery -ve or 0 volts, a large current will flow through the lamp which lights it up and you will find that the voltage will drop to 0 (or there is +12 volts across the lamp)

 

You will not be shorting out the battery as the lamp is between the terminals doing what it should (lighting up) and the resistance of the lamp determines its power rating.

 

(2Bbuilt - if you have no power on either side, then the ignition switched live is not getting there and you need to find out why)

 

Note - you cannot just measure the resistance of a lamp when cold as it will give too low a reading. Resistance of metals increases when they get hot which is why there is a large surge current through tungsten lamps when cold - this is the reason they always fail when you turn them on and not usually when they are lit)

 

Since Power = Volts x Current you can work out the current (E.g 60 Watts @ 12 volts => 5 amps). Then you can work out from the fact that Power also = Current squared x Resistance.

 

I.e 60 Watts = (5x5) x Resistance. So the resistance should be 2.4 ohms WHEN HOT (which you cannot measure). You will find the resistance when cold will be much lower than this for a 60 Watt lamp.

 

Hope that helps?

 

Simon.

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To answer the question posed by Alan above.

 

If you attach one side of a lamp to battery +ve (12 volts) and measured the unconnected side to the battery -ve (0 volts) with a multimeter set to volts, you will find that there is +12 volts there.

 

The reason is that the volt or multi meter is a very high resistance instrument and draws almost zero amps. (The lamp will also not light up) Once you connect the other side of a lamp to the battery -ve or 0 volts, a large current will flow through the lamp which lights it up and you will find that the voltage will drop to 0 (or there is +12 volts across the lamp)

 

Perfect , thanks, never too old to learn :)

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The wire colours for the gauges was pretty standard for sierras. However the positions of the wires in the plugs was variable. I will post a pic which shows one type of sierra dash, not yours unfortunately, which at least gives you the colours.

For the dash to work you must have an ignition live feed, BK/Y, which supplies power to the warning lights and gauges. You must also have an earth, BN. The low brake fluid, ignition and oil pressure warning light bulbs are all fed from this 12v ignition live. Each then has a wire from the earth side of the bulb to a 'target sensor'. Low brake fluid goes to the reservoir sensor and on to the handbrake switch. Ignition goes to the alternator. Oil pressure goes to the oil pressure switch. LBF/H and OIL become an earth when activated by what its supposed to be sensing. The IGN is an earth when the alternator is not producing.

The gauges will only work if they have a live feed and an earth, as well as a wire to their sender.

Indicators warning is completely independent of live and earth and main beam warning does need the earth.

 

If your dash is sierra the colours should be right. The positions of those colours won't be.

 

Nigel

 

 

 

post-21-0-73778300-1439546114_thumb.jpg

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Guest 2Bbuilt

post-13416-0-67938300-1439559660_thumb.jpg

 

ok

 

i have no power to the brake light and alternator lights, but the oil light does work (which means i have switched power).

 

from the circuit diagram (attached) it looks like 12v (black/yellow) feeds the voltage stabilser, and then feeds out to the 3 lights (alternator, oil and brake).

 

if only 1 is working i assume then that the issue is with voltage stabiliser circuit.

 

if i short 12v to the light circuit and bypass stabiliser, they should work? right?

Edited by 2Bbuilt
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Guest 2Bbuilt

Thanks to all for the help

 

its now fixed

 

schoolboy error was the issue ........ it works much better now the switched live is connect to the correct wire!!!

 

must of been my helper ..

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