How to test "oil" light
Thread Starter
2nd Gear Member
Joined: Jan 2008
Posts: 152
From: Utah
How to test "oil" light
On my 65 mustang I would like to test the oil light and make sure it works. The "ALT" light comes on when the ignition is turned on and then goes out once the engine starts. How can I make sure the oil light works? Thanks.
6th Gear Member
Joined: Oct 2006
Posts: 6,417
From: Cork, Ireland
Hiya...
check the other way round, it's easier
there's a cable at engine that connects to the oil pressure sensor in engine. This is close to the oil filter (it should be the only cable near your oil filter going directly to the engine).
leave ignition on and disconnect it from the oil pressure sensor.
connect the contact of this cable directly to battery minus. You might need to extend the cable temporarily with some speaker cable or whatever you have lying around.
When you do that the light should come on.
If the light comes on you know its the sensor or the contact at the cable. So clean it all and try hooking it up normal again to see if that helped.
If the light stays off the next step would be to clean tyhe connectors at your firewall. See if that works.
Basically the way it works is the oil pressure switch is mounted directly to the block (which is grounded). So if there's no pressure the switch is closed and the switrch will ground this cable, which will cause the light inside to go on if the other side of light is positive. if oil pressure is there the switch will disconnect the cable from ground so the light will never come on. hope that makes sense to ;you.
I'm only suggesting to try it this way round, because you can already eliminate a few trouble points without even touching a screwdriver
If you say: no I want to check the lamp first, then the easiest way is to disconnect speedo cable from the gauge cluster, unscrew the cluster.Pull it out and swap the two idiot lights (OIL and ALT). If the alt stops working then you know the lamp was fried ...
check the other way round, it's easier
there's a cable at engine that connects to the oil pressure sensor in engine. This is close to the oil filter (it should be the only cable near your oil filter going directly to the engine).
leave ignition on and disconnect it from the oil pressure sensor.
connect the contact of this cable directly to battery minus. You might need to extend the cable temporarily with some speaker cable or whatever you have lying around.
When you do that the light should come on.
If the light comes on you know its the sensor or the contact at the cable. So clean it all and try hooking it up normal again to see if that helped.
If the light stays off the next step would be to clean tyhe connectors at your firewall. See if that works.
Basically the way it works is the oil pressure switch is mounted directly to the block (which is grounded). So if there's no pressure the switch is closed and the switrch will ground this cable, which will cause the light inside to go on if the other side of light is positive. if oil pressure is there the switch will disconnect the cable from ground so the light will never come on. hope that makes sense to ;you.
I'm only suggesting to try it this way round, because you can already eliminate a few trouble points without even touching a screwdriver
If you say: no I want to check the lamp first, then the easiest way is to disconnect speedo cable from the gauge cluster, unscrew the cluster.Pull it out and swap the two idiot lights (OIL and ALT). If the alt stops working then you know the lamp was fried ...
5th Gear Member
Joined: Feb 2007
Posts: 2,688
From: Ramona, CA
Also, does anyone know if it is ok to use a brass fitting instead of that long sending unit shaft to attach a sending unit and a mechanical oil guage at the same time? Im only using the mechanical guage fitting attached directly to the block right now and the last time my wife drove the car she scared me by telling me that the oil pressure needle never moved when she was driving.. Of course it didnt, she was looking at the dash guage thats not hooked up.. Its one of those things that I need to get fixed.. You know, those little things..(a PITA)
6th Gear Member
Joined: Oct 2006
Posts: 6,417
From: Cork, Ireland
so first of all:
- key in off position both lights are off
- then turn key into ignition position both lamps should come on
- then start car both lights should come off.
the car is wired in such a way that both lights will always be on when key in ignition and car not running. It's for checking if the lights actually work. every single car does that by the way. modern or not.
so yes. the oil pressure sensor is a very cheap switch.
If there is no pressure then it directs the attached cable straight to ground. Then the light will come on.
So if you take this cable directly from the oil pressure switch and connect it to ground or battery minus then the light should come on.
Hope it makes sense. if not just keep asking ... i'll paint a diagram then ... ;-)
the logic goes:
ignition plus -> oil pressure light-> red/white cable ->main connector on firewall ->red/white cable->oil pressure switch connected to ground.
a lamp only burns when you have plus on one side, minus on the other.
Kalli
- key in off position both lights are off
- then turn key into ignition position both lamps should come on
- then start car both lights should come off.
the car is wired in such a way that both lights will always be on when key in ignition and car not running. It's for checking if the lights actually work. every single car does that by the way. modern or not.
so yes. the oil pressure sensor is a very cheap switch.
If there is no pressure then it directs the attached cable straight to ground. Then the light will come on.
So if you take this cable directly from the oil pressure switch and connect it to ground or battery minus then the light should come on.
Hope it makes sense. if not just keep asking ... i'll paint a diagram then ... ;-)
the logic goes:
ignition plus -> oil pressure light-> red/white cable ->main connector on firewall ->red/white cable->oil pressure switch connected to ground.
a lamp only burns when you have plus on one side, minus on the other.
Kalli
4th Gear Member
Joined: Jun 2006
Posts: 1,483
From: Fontana, California
Hiya...
check the other way round, it's easier
there's a cable at engine that connects to the oil pressure sensor in engine. This is close to the oil filter (it should be the only cable near your oil filter going directly to the engine).
leave ignition on and disconnect it from the oil pressure sensor.
connect the contact of this cable directly to battery minus. You might need to extend the cable temporarily with some speaker cable or whatever you have lying around.
When you do that the light should come on.
If the light comes on you know its the sensor or the contact at the cable. So clean it all and try hooking it up normal again to see if that helped.
If the light stays off the next step would be to clean tyhe connectors at your firewall. See if that works.
Basically the way it works is the oil pressure switch is mounted directly to the block (which is grounded). So if there's no pressure the switch is closed and the switrch will ground this cable, which will cause the light inside to go on if the other side of light is positive. if oil pressure is there the switch will disconnect the cable from ground so the light will never come on. hope that makes sense to ;you.
I'm only suggesting to try it this way round, because you can already eliminate a few trouble points without even touching a screwdriver
If you say: no I want to check the lamp first, then the easiest way is to disconnect speedo cable from the gauge cluster, unscrew the cluster.Pull it out and swap the two idiot lights (OIL and ALT). If the alt stops working then you know the lamp was fried ...
check the other way round, it's easier
there's a cable at engine that connects to the oil pressure sensor in engine. This is close to the oil filter (it should be the only cable near your oil filter going directly to the engine).
leave ignition on and disconnect it from the oil pressure sensor.
connect the contact of this cable directly to battery minus. You might need to extend the cable temporarily with some speaker cable or whatever you have lying around.
When you do that the light should come on.
If the light comes on you know its the sensor or the contact at the cable. So clean it all and try hooking it up normal again to see if that helped.
If the light stays off the next step would be to clean tyhe connectors at your firewall. See if that works.
Basically the way it works is the oil pressure switch is mounted directly to the block (which is grounded). So if there's no pressure the switch is closed and the switrch will ground this cable, which will cause the light inside to go on if the other side of light is positive. if oil pressure is there the switch will disconnect the cable from ground so the light will never come on. hope that makes sense to ;you.
I'm only suggesting to try it this way round, because you can already eliminate a few trouble points without even touching a screwdriver
If you say: no I want to check the lamp first, then the easiest way is to disconnect speedo cable from the gauge cluster, unscrew the cluster.Pull it out and swap the two idiot lights (OIL and ALT). If the alt stops working then you know the lamp was fried ...
