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Triumph TR6 - Oil Presure Warning Light

Started the TR6 for the 3'rd time this season and now have the Oil Pressure Warning Light illuminate faintly under acceleration, but the Brake Warning Light stays off. Oil Pressure Gauge reports normal, oil level normal & clean from an oil change back in mid Sept.

Both Oil & Brake lights are on with the ignition on but not started, and the Oil Pressure Warning Light stays on under (very) low revs, which is proper (or normal for my TR).

The Oil Pressure Light then goes out under normal idle, but when the accelerator is depressed, the light comes back on faintly.

I read the white manual and it mentions to expect both lights to illuminate faulty under low oil pressure, but as mentioned the gauge is reading and reacting proper.

Any suggestions?

P Johnston


Are you sure that you aren't getting some very low glow from the brake warning light? I had as similar issue when I first got my TR6. The brake warning light glow was only visible when it was shielded from light or it was dark. If you are getting a low glow there and at the oil pressure light, your PDWA shuttle piston is not centered. Two ways to center it, one is to remove the PDWA switch and use a small screwdriver to center the valley of the piston under where the switch pin goes (do not put alot of load on the piston when doing this). The other is to bleed the brakes to center the piston.

No faint glow from the Brake Warning Light.

It's wierd, because when idling, the Oil Pressure Light is off, but when I rev it, it glows faintly.

P Johnston

That circut is so screwed up it's ridiculous. The pressure switch on mine has never worked, and resisted all attempts to fix it.

Brent B

Is the Pressure Gauge Switch the same one for the Pressure Warning Light? If so, I suppose it could be possible for only the light portion to fail.

Hoping for suggestions prior to re & re'ing the oil pump as the only option to ensure all is ok in the sump.
P Johnston

Peter, the guage is mechanical ie it's not linked to wiring (except for the bulb) and if I recall correctly, it actually has a line from the motor with oil.

The Pressure warning light is seperate, and althought I can't give you advice on you're problem, I will say that the Bently manual is not accurate in describing the link with the brake light for all model years. My car is '76 and it operates different from every other year. ie. my brake failure light does not glow on ignition. Even the famous Dan Master book fails to mention this odd variation.

At least now you can look at your oil pressure and perhaps determine if this problem is electrical or real oil pump / pressure problem.
Mati Holland

Light has no relation to the gauge circuit-wise. If there is a conflict of information between the two, the gauge wins. I don't believe I could see my OP light glowing in full sun. I don't know if Brent has given up on resolving his, but I would after a few hours of tinkering.

Have you verified it's wired right at the sender? I have a three wire sender. If you've done any work in the area, it is possible the wires went back on wrong. From what I hear, this can also be a common cause of dieseling after shutdown.

Don from Jersey
D Hasara

"My car is '76 and it operates different from every other year. ie. my brake failure light does not glow on ignition. Even the famous Dan Master book fails to mention this odd variation."

Yes it does! See text and figures 7 and 8, page 92.

Peter, what year is your car?
Dan Masters

So the Sending Unit is for the Light and not the Gauge?

As mentioned above, the Sending Unit was replaced approx. 3 Yrs. ago and the oil light has worked without issues until a couple of days ago (so I believe the 3 wires to be on correctly).

Perhaps time to replace it before looking in the sump, being that the gauge is reading and reacting properly.

P Johnston

Geez...sorry Dan. I must have gone blind searching for that reference.
Mati Holland


The gauge is pure mechanical, not electrical. Your OP light issue is electrical in nature. It's either miswiring or bad sending unit. Wish I could help with it, but I'd rather defer to Mr. Masters on this one. I've heard too many horror stories of miswiring the sender. This is why I keep a digital camera handy to document everything before I screw it up! Even with photographic evidence, I still get it wrong most times.


D Hasara

Removed the Oil Sending Unit yesterday. Isn't there suppose to be a ball bearing located inside at the end of the unit? I do recall it not being "fully" open. If so, it's no longer there, which means the unit has gone defective.

Hopefully it's either inside the Sending Unit, or in the bottom of the sump at the magnetic drain plug.

Either way, replacing the Oil Sending Unit this week.

Will advise...
P Johnston

No ball bearing to loose. Not really sure if it has one but if it does then it would be captured behind the hole in the threaded end. I know you do not put a ball bearing in then screw in the sender. I have never taken a OP sender switch apart but it must have an electrical contact inside that "makes" the circuit on low OP. I suppose it could be a small ball bearing making contact with the end of the threaded area. This makes sense to me as you have the OP light on at start up then OP pushes the Ball Bearing away from the end. I also can imagine this BB being spring loaded. For sure a change of the sending unit will fix or eliminate it from the equation.
I agree with others, your OP gauge is the on to read as it is 100% operated by true oil pressure.
Rick C
Rick Crawford

Well, I replaced the OP Sending Unit, and it still illuminates under acceleration, but is off at idle.

Oil Pressure is good according to the gauge.

Can't think what else to check other than the Oil Pump.

P Johnston

Ok, I need to verify the OP Sending Unit connections. My TR6 is a '75.

Best that I can tell from the wiring diagrams and the in-car functionality, the wiring should be

Top - White/Purple
Left - White/Brown
Bottom - Black

This is different than listed in an archive post where it says:

Top - Black
Left - White/Brown
Bottom - White/Purple

Also, I'm trying to trace the wiring diagram to see if having installed an audio capacitor (this spring) in parallel with the audio amp is what is causing my issue.
P Johnston

Not sure what top bottom and left older TR ('71)only has one wire to my simple switch.

Bottom line is that:W/P (terminal I)goes to anti run- on valve, B (terminal P) goes to ground, and W/N (terminal S) goes to low oil pressure lamp. I would go by the schematic not an archive. Since it worked before, I would say your wiring is correct. I do not think your radio has anything to do with this.

Operation: With ignition in on position you have contact between terminals P&S....lamp is on. When engine running and OP comes up switch "switches" to terminals I&S...lamp goes out. The only way you can have that lamp on when it is not suppose to be on is to have a voltage level on terminal S... W/N wire (Put voltmeter black lead on BAT- terminal). Take a voltage reading on this terminal at idle and then rev the engine up a bit. You should have a constant 0 volts reading. With the OP switch in hand, you should read infinite OHMS between terminals I&S and same between terminals I&P. Terminals P&S should be low reading OHMS.

Try disconnecting the brake failure switch wire and see if the bulb goes out....a long shot:)
Rick C
Rick Crawford

Still looking for a miracle.

I've verified that the new Oil Pressure Switch is wired correctly, and both the Oil Pressure Light & the Brake Light glow with the ignition on but the engine not started.

When idling normally, both lights are out, but when the accelerator is depressed, the Oil Light glows, almost glows more in intensity the higher the revs are.

I've talked to a couple of folks, all of which say that under low oil pressure both lights should illuminate, but my Brake Light is definitely off. Not to mention that there is more oil pressure under acceleration.

The Oil Gauge is reading normal, but as a precaution I dropped the Sump and replaced the Oil Pump.

What a dirty job (from the outside of the engine of course), no hoist. Anyway, the original-? Oil Pump was somewhat pitted and scowered. The Sump was without sludge, the engine was very clean on the inside with no carbon build-up, and the Thrust Washer visibly looked fine. (50,000 orig. miles).

Did an extra good job of removing the gasket, and seated a new one to the Sump.

New filter & oil, and we're without any leaks and have lots of pressure, but the Oil Light is as before.

Tried disconnecting the Brake Switch, and the Oil Light still illuminates as above.

Try another switch?
P Johnston


You must have a miswiring somewhere in your car. If it is wired correctly, there is no way the oil switch can operate the oil warning lamp and not light the brake switch.

Try these tests and let us know the results:

1. Remove the white/brown wire from the oil pressure switch and turn the key on. You should have no lights on, neither the brake nor the oil warning lamps.

2. Connect the white/brown wire to ground and turn the key on. Both lamps should light at half intensity and stay lit even if the engine is running and the oil pressure is up.

3. Connect the white/black wire from the brake failure switch (PDWA) and turn the key on. The brake warning light should come on and stay on, engine running or not, white/brown wire from the oil pressure switch grounded or not.
Dan Masters

As per Dan's instructions I would say he has a bad ground(who'd have thunk that?).

The cloudy mystery is starting to clear. Turns out that the Ignition Lamp and Oil Lamp sockets were reversed within the tach, which explains the condition I observed (see above). Also, the Oil Lamp (which was in the Ignition spot), had a suspect bulb.

So, the Oil Lamp mystery is solved, and I believe that with the Ignition Lamp now staying illuminated at revs above idle, reflects a defective alternator which (hopefully) resolves my 3-Yr. old issue of what I thought was a short (being that the battery wouldn’t keep a charge).

Lessons learned? Too many to list…

Thanks to all for feedback & assistance.
P Johnston

Closing Comments:

So it was the Alt.

Took it to Master Rebuilder (Ossington north of Queen St. W), and had it rebuilt and returned in under 24hrs. Price was very competitive.
P Johnston

Well, at least you know you have a new oil pump and your thrust washer looks OK now. Maybe even stopped a bit of "marking its territory".

This thread was discussed between 09/04/2005 and 21/04/2005

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