oil pressure warning light

[dagest13]

The amber oil pressure warning light on the speedo face of my '65 MM is permanently on! I have changed filter and oil, flushing through with Morris flushing oil before refilling. Could this be an electrical fault? (I recently had the ignition coil replaced and the problem has dated since then.) Also, I've lost my horn (very nasty!) despite the fact that the connections all seem to be in order. I love my car but I'm a real dummy when it comes to sorting out problems and my local garage look at a real engine, and scratch their heads! Any advice would be really appreciated! Thank you.

[firedrake1942]

The sender on a 1098 engine sits just under the coil so I would start there first. Something may have been disturbed / shorted when the new coil was fitted. This does not explain the horn tho. A look at the wiring diagram to see if the two feeds intersect anywhere and whether in fitting the coil / disturbing wiring something happened. Look at fuses first. I have frequently forgotten this advice only to find that a broken, / blown fuse is the answer.

[firedrake1942]

Sorry thats the water temp sender. The oil sender is by the distributor. Was any work done on that ?

[Trickydicky]

If you have the standard filter assembly the "blocked oil filter" light connection could be not connected.

[Budgie]

Try a new oil switch as these can fail .I put a new one on my tourer last year and barely 6 months later I had to buy another as , like you, my amber oil light would not go out but I new it wasn't the oil pump as I have an oil pressure gauge fitted. So one new oil switch later and all's working well with the light going out as and when it should.

[dagest13]

Thank you all for your very helpful advice. I will check out your various suggestions and let you know how I get on!

[olderisbetter]

The wire could be earthed somewhere else, My 58 traveller had the sender wire caught in the speedo bracket at some point making the light stay on and they ran a new wire from the sender to fix it, If you pull the wire off and the light stays on it must be getting earthed closer to the bulb, it may be simpler than it seems, a bit like me...

[dagest13]

Thanks for all the advice, especially from my latest help mate 'olderisbetter'. I've tried them all but with no luck as yet. Any one know of a reliable MM mechanic in the south hants area?

[oliver90owner]

You may need luck if the pressure really is low.

As suggested earlier, the lamp should be extinguished if the lead to the pressure switch is disconnected (if a simple pressure switch). Otherwise, there is an electrical fault. Have you determined if it is a wiring fault?

If not an obvious wiring fault, my advice is to substitute a pressure gauge for the warning light switch and ascertain whether the pressure is low or normal, PDQ. A pressure gauge is cheaper than an engine rebuild, or a replacement engine....

[dagest13]

Many thanks for this! I did wonder if the wires had got mixed up when the ignition coil was replaced recently. I checked the wiring colours according the wiring plan in my Haynes manual, and found the wire to the oil switch to be different to that on the plan. When I disconnected this, the ignition light went out! I have tried several combinations in order to replicate the wiring plan, but have yet to have found one which switches off the oil pressure light. I will ask my local garage if they are able to fit the pressure gauge as suggested.
Thanks to everyone!
p.s. At one stage a second amber light situated above the red ignition light was illuminated. Anyone tell me what this is for?

[liammonty]

That is supposed to be the oil pressure warning (i.e. the amber light above the red one)... the one on the left side of the speedo (if fitted) is the blocked oil filter warning (which someone mentioned previously). Sounds like they are all mixed up. You really need to establish what is what before you can sort it out - it sounds as though your problem may be with the unreliable blocked filter warning, and that the oil pressure is not a problem, and the oil pressure warning light isn't actually coming on. What is odd though is that the light that should actually be the oil pressure warning has only come on once, according to what you said.

If it transpires it's the blocked filter light that's on all the time, just disconnect it, as you don't need it, assuming you change the oil and filter when you should