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TR6 Oil Pressure Switch
- Thread starter rh18246
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dklawson
Yoda
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I was looking at the Advance Auto Wire schematic for your car and noticed it has the multi-pin pressure switch that is wired together with the brake warning light. It looks like the power for the oil warning lamp must first pass through the brake warning lamp. If the brake warning bulb is burned out or otherwise has problems then the oil pressure lamp should not work. You may be getting voltage from somewhere else during your measurements.
What is the status of the brake warning light? Unplug the PDWA connector and measure the voltage between chassis ground and the pins in the PDWA plug. If the bulb and its wiring are intact you should find 12V with the ignition in the run position. That same 12V would also go to power the oil pressure warning light.
See the top left corner of page 7 in the PDF linked below.
https://www.advanceautowire.com/tr2506.pdf
What is the status of the brake warning light? Unplug the PDWA connector and measure the voltage between chassis ground and the pins in the PDWA plug. If the bulb and its wiring are intact you should find 12V with the ignition in the run position. That same 12V would also go to power the oil pressure warning light.
See the top left corner of page 7 in the PDF linked below.
https://www.advanceautowire.com/tr2506.pdf
poolboy
Yoda
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The OP sensor and the switch screwed into the PDWA are for providing a ground for the warning lamps and the Anti Run-on Valve.
The OP sensor provides a ground for the low OP warning lamp if no OP (less than 5psi ?) is sensed..the OP warning lamp AND the BRAKE warning lamp will glow dimly if the ignition key is ON (RUN) in that event.
The OP sensor provides a ground for the Anti Run-on Valve as long as there is OP...however the ARV only gets juice when the key is OFF
The Switch screwed into the PDWA grounds the BRAKE warning lamp if the shuttle in the PDWA shifts position..The BRAKE warning lamp will glow brightly.
The OP sensor provides a ground for the low OP warning lamp if no OP (less than 5psi ?) is sensed..the OP warning lamp AND the BRAKE warning lamp will glow dimly if the ignition key is ON (RUN) in that event.
The OP sensor provides a ground for the Anti Run-on Valve as long as there is OP...however the ARV only gets juice when the key is OFF
The Switch screwed into the PDWA grounds the BRAKE warning lamp if the shuttle in the PDWA shifts position..The BRAKE warning lamp will glow brightly.
Thank you, I have changed all the bulbs, but the brake warning light is not working either, the brake pressure switch has a single wire leading to it, but that shows no voltage at all. I have cleaned all the contacts with contact cleaner and fine emery cloth but nothing registers. The anti run on system is no longer fitted to the car, removed by the previous owner.
dklawson
Yoda
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Presumably Matthew was looking for 12V on the disconnected PDWA plug based on my previous post. If two additional steps are taken, you will find 12V on the PDWA plug when the brake warning lamp/bulb and wiring are functioning correctly.
If you have a working parking brake warning switch, make sure the parking brake is off. Also make sure the white/brown OP switch wire is disconnected and that the disconnected wire is not touching ground. When there are no possible ground paths (via OP switch or parking brake switch) the PDWA wire should be hot when the ignition is on. If it is not, the bulb is bad or the feed from the ignition switch may be bad. Some PDWA plugs do not have the two pins tied together in the connector so check for voltage between each and ground.
I'm sorry that I forgot to mention disconnecting the white/brown wire and the releasing the parking brake in my previous post. However, it doesn't look like Triumph/Lucas changed the warning light circuit or added the parking brake switch until '76 and Matthew said this is a '74.
Don, which part do I have backwards?
If you have a working parking brake warning switch, make sure the parking brake is off. Also make sure the white/brown OP switch wire is disconnected and that the disconnected wire is not touching ground. When there are no possible ground paths (via OP switch or parking brake switch) the PDWA wire should be hot when the ignition is on. If it is not, the bulb is bad or the feed from the ignition switch may be bad. Some PDWA plugs do not have the two pins tied together in the connector so check for voltage between each and ground.
I'm sorry that I forgot to mention disconnecting the white/brown wire and the releasing the parking brake in my previous post. However, it doesn't look like Triumph/Lucas changed the warning light circuit or added the parking brake switch until '76 and Matthew said this is a '74.
Don, which part do I have backwards?
TR3driver
Great Pumpkin - R.I.P
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With the key on, you should find voltage at the PDWA wire, even with it connected to the PDWA. If there is no voltage even with it disconnected, then there is a problem at the brake warning lamp; perhaps the bulb is not making contact or a wire is broken. Recheck for power at the lamp. There is no fuse in this circuit, so that should not be a problem (unless someone has changed the circuit, which is always a possibility).
If there is voltage with it disconnected, but "goes away" when connected, then the PDWA switch is grounding the wire. That will keep the oil pressure light from working. You should see the brake warning lamp come on but again there could be a problem with the wires, bulb, or connections between them.
This is the same as what Doug said, just restated. I don't think he had anything backwards.
If there is voltage with it disconnected, but "goes away" when connected, then the PDWA switch is grounding the wire. That will keep the oil pressure light from working. You should see the brake warning lamp come on but again there could be a problem with the wires, bulb, or connections between them.
This is the same as what Doug said, just restated. I don't think he had anything backwards.
dklawson
Yoda
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Don, which way are you following the current/voltage path? In Lucas wiring the white wires are switched, un-fused so they will be hot when the ignition is on. In this circuit the white wire comes from the ignition switch and (up to '76) the current has to flow through the brake warning light before passing through the OP light on its way to ground through the OP switch.
Take a look again at the top and slightly to left of center of page 7 in the PDF linked below for the '74 TR6 OP switch schematic.
https://www.advanceautowire.com/tr2506.pdf
Take a look again at the top and slightly to left of center of page 7 in the PDF linked below for the '74 TR6 OP switch schematic.
https://www.advanceautowire.com/tr2506.pdf
Ok so I have checked everything....I have power at both brake warning light and OP warning light bulb holders, when bulbs are in holders nothing......but if I connect bulb to outside of holders metal case and then earth bulbs the lights work as they should
Does this mean the bulb holders are the issue? OP light glows very faintly with a lot of jiggling sometimes.....
Does this mean the bulb holders are the issue? OP light glows very faintly with a lot of jiggling sometimes.....
[h=2]Re: Oil Pressure Switch[/h]
Ok so I have checked everything....I have power at both brake warning light and OP warning light bulb holders, when bulbs are in holders nothing......but if I connect bulb to outside of holders metal case and then earth bulbs the lights work as they should
Does this mean the bulb holders are the issue? OP light glows very faintly with a lot of jiggling sometimes.....
Does this mean the bulb holders are the issue? OP light glows very faintly with a lot of jiggling sometimes.....
TR3driver
Great Pumpkin - R.I.P
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Sorry, I'm confused by that statement. Do you mean you find power only when the bulbs are not in the holders?
dklawson
Yoda
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In normal operation, the bulb holders are not supposed to be a ground connection for these circuits. When the PDWA spool shifts, the switch in it completes a path to ground for the brake warning lamp. When the ignition is on and the engine off, the OP switch provides a path to ground for the oil warning lamp (and because it is in series... a ground path for the brake warning light also).
If you leave the ignition on, disconnect the white/brown wire at the OP switch, and move your circuit tester so it is located between ground and the terminal on the end of the white/brown wire, does the circuit tester light and do the dash warning lamps light? If you leave the ignition on, unplug the PDWA connector and move your circuit tester so it is located between ground and the terminals (check both terminals one at a time) in the PDWA plug, does your tester light? Does the brake warning lamp light?
If you leave the ignition on, disconnect the white/brown wire at the OP switch, and move your circuit tester so it is located between ground and the terminal on the end of the white/brown wire, does the circuit tester light and do the dash warning lamps light? If you leave the ignition on, unplug the PDWA connector and move your circuit tester so it is located between ground and the terminals (check both terminals one at a time) in the PDWA plug, does your tester light? Does the brake warning lamp light?