oil pressure warning light

[juanbenae]

looking to install some more effective warning lights for oil pressure and alternator fail and was wondering which side of the gauge wiring to land the power side of the new lamps to?? i would assume the power side, but was wondering if the grounded side of the light would keep the light on at all times by completing the circuit. would the switch side of the light be where i need to place it so it only illuminates when the switch for low pressure completes the circuit? i know there were good instructions for the big red oil light install here at one time, i can not find them via search and website is no longer being hosted so the online instructions can no longer be had.

tia,

toby

[Joe Bob]

Hook it into the same circuit as the dash warning lights that come on when you turn the ignition on.

[juanbenae]

Originally Posted by Joe Bob

Hook it into the same circuit as the dash warning lights that come on when you turn the ignition on.

yeah there are two leads off the in gauge light, one power and one from the oil pressure sensor switch. i am loking to see which side of that the hot wire from my new lamp fixture would go to. thanks for your time though mike.

[Joe Bob]

Sorry, + side and give it it's own ground.

[juanbenae]

done that and as id expected the grounded lamp stays illuminated after the in gauge light shuts down when the cars runs and the oil presure gets up.

anyone have the wiring diagram from the big red oil lamp or other like install?

thanx for stickin with me on this one mike ; )

[juanbenae]

should note the lamps i am using are self grounding with the mounting screw. i think what id suspected regarding its own ground with it powered from the hot side of the in gauge lamp means even after the pressure gets up the new lamp circuit remains complete so it stays on.

what i need to know is when wiring a second lamp do i need to ground it to the other side of the in gauge light? ground would be achieved that way only when the pressure gets low and ground is provided by the pressure sender in the motor? HELP

[Mahler9th]

I am pretty sure that the typically installed 911 oil pressure switches go to ground at the pressure set point. So if the lead from such a switch goes to a 12 volt lamp, and the other side of the lamp's wiring is attached to +12 volts, the lamp will illuminate when the pressure goes below the set point.

I decided to buy one of the adjustable pressure switches from SmartRacing Products. You can adjust the set point. Once it is reached, ground is provided. I used a $5 generic trailer type 12 volt red lamp (about 2 inches in diameter) in my dash which is wired on one side to the adjustable switch, and on the other to +12 volts (when ignition is on).

As I have stated in other threads, more than one expert has suggested to me that these warning lights have marginal benefits-- often once the pressure goes to the low set point, it is already too late.

At any rate, Craig Watkins/Jerry Woods suggest adjusting the switch I have to be set at a fairly high oil pressure when the car is at idle and the oil is warm. Theoretically that will give an earlier warning than a typical non-adjustable switch in some failure modes.

If attaching to the existing circuit in a 911, I'd just run the wire that comes from the switch to the new lamp, and the other side of the lamp circuit to a +12v source that is on with iginition.

Happy New Year.

[Mahler9th]

I don't think the light you are using can be spliced into the existing circuit. I don't think you should use a light that doesn't have two terminals. The light I used was about $5 at NAPA... happy to rig one up for you.

- Mike

[Walt Fricke]

311:

First off, be sure you understand that the stock oil pressure idiot light switch just closes a contact to ground when the oil pressure gets below about 0.4 bar (about 6 psi). So your circuit goes like this: +12 volt source to light bulb to switch (whose case is grounded) and ground. Not complicated. As Mike said, any source of ignition switched 12 volts will do to source your current to light a bulb which you add in a differnt place on the dash.

I've got an Autometer 30 psi idiot light sender in my race motor, which has 1/8" NPT thread. Your engine case has M10x1 thread, which is close to the NPT, but not the same. So you need an adapter to run this kind of switch (comes in several pressure settings). Or just purchase the SRP parts. That's all that is needed to make this warning light actually useful while driving.

It saved a motor of mine at a race track: Wife (who was first out on the track): "The big red light came on almost right away, and slowing down didn't make any difference, so I slowed some more and came right in." A #5 rod bearing had gotten down to the copper, but a little coppery color to the crank journal was all the additional damage. Since neither of us had driven that track before, I doubt either would have noted that the oil pressure gauge itself wasn't showing as much as was required before the engine blew up.

Making that light brighter in its stock location is much harder. You'd need a brighter bulb, and that is not as simple as it sounds, as it has to fit the insulated holder. So if you really worry about it (this is mostly a race track modification), do what Mike did and put a red trailer light where the clock would be. You could run that in parallel with the oil idiot light on the dash - both of them can get their ground through the idiot switch. But that's for a track car - don't need no stinking clock. Of course you could put some other light elsewhere as well.

The oil idiot light part is simple.

But you also mentioned the alternator warning light (which additionally serves to warn you if your fan belt broke or came off, which is much worse than having a failed alternator because you really need that fan). There is no simple way of making this light more prominent.

It is complicated because the light bulb is part of the alternator/voltage regulator circuit. If the bulb is burnt out, there is a chance that your alternator won't work. The bulb's resistance has to match what the alternator/regulator needs to get started (to excite the diodes). When Porsche changed some of this, they had to change the bulb as well, and us shade tree guys who changed alternators around usually wired a resistor in parallel with the bulb (new bulb required different housing, some complication like that). Porsche has a technical bulleting explaining this.

So you can't just go plugging in some big bright light bulb expecting it to work in a simple manner like the oil idiot light. You'd have to come up with a very high impedence circuit which would sense when the light was on (so as not to mess up the alternator's job), and use that to turn on a relay or power transistor to turn on a bigger light elsewhere. Something like that. If I had to guess, designing and building such a circuit might be difficult for you (it would be for me, though if I thought this was useful I might give it a try just for the education such projects produce - an optoisolator maybe?).

[Gunter]

car 311,

Get an extra light with 2 leads; one for power, the other for ground.
You also need the little dual Faston connector that allows you to make extra Faston connections without splicing the wires.

Like others said, use any switched 12 V source and wire it to extra light/lamp.
Then run the second wire from the light to the oil pressure switch on top of the engine or tap into the ground wire coming from the oil pressure switch to the existing warning light in the dash.

The oil pressure switch on top of the engine is basically a ground provided by oil pressure; with no pressure, ground is provided and light comes on.

IMHO, no need for an extra warning light when the Alternator fails due to the belt breaking or whatever reason, because all lights will come on in the dash as experienced several times by yours truly.

My extra light is visible in the center console:

[juanbenae]

thanks all who replied with further insight!

walt, was not aware of the complexity regarding the alternator lamp. i have researched many threads, an example here>>>
My little big oil pressure warning light.

there is no mention of the alternator interference you note. seems a bit unorthodox to have such a tiny bulb play such an important role in that vital circuit?? the bulb and fixture for the in gauge lamp look no different from the oil warning light units. in fact the power lead for the oil warning light is jumpered from the alternator fixture?? not doubting your insight, just wondering if what you note is a specific era car, mine is a 78 3.0l. request further discussion on this by the brain trust here.

gunter- you note that all gauge lights will illuminate. this being a race car i have stripped all dash lighting sans the oil and alt warning lights so i still am hoping to figure a way to have the light be more apparent.

thanks again, & look forward to further discussion on walts point on the alt wiring.

toby

[Gunter]

Most systems are the same on many cars, Porsche included.

The bulb-size for the Alternator charging light is critical and a search on Alternator-function will give you info why like: field current for "bootstrap" function etc.

I wouldn't fuch with it.
You could install a tension switch on the fan belt like the 993's have; easy to wire up.

The oil warning light is very simple: Any switched power will do because the oil pressure switch on to of the engine supplies ground. You can just go parallel to the existing wiring on the light in the dash.

Keep it simple.

[dshepp806]

Originally Posted by Gunter

Most systems are the same on many cars, Porsche included.

The bulb-size for the Alternator charging light is critical and a search on Alternator-function will give you info why like: field current for "bootstrap" function etc.

I wouldn't fuch with it.
You could install a tension switch on the fan belt like the 993's have; easy to wire up.

The oil warning light is very simple: Any switched power will do because the oil pressure switch on to of the engine supplies ground. You can just go parallel to the existing wiring on the light in the dash.

Keep it simple.

+1 on making use of that ground command....don't frick with the bulb (at all).

Doyle

[Walt Fricke]

Toby

In 1995, Porsche published "Parts and Technical Reference Catalog, 911 Models 1974-1989." 8 1/2" x 11", about 130 pages, paperback. Alas, out of print, but well worth having if you can find a used one. Iit has, along with part numbers for most of the things that might need replacement, some technical bulletins. At page 111 we find page 2 of the Tech Bulletin on "New Alternator has integrated Regulator," which generally discusses how to switch from the old alternator with the external regulator to the new one for 1974-1983 911s.

Here we find: "NOTE: If battery charge indicator lamp does not go out after starting engine, the exciter current is too weak because of 2 watt lamp. In this case, supplied resistor, part number 911 641 981 (91 ohms, 5 watts) must be installed parallel to battery charge indicator lamp."

It goes on to describe and illustrate how to install the resistor. And ends with:
"CAUTION: 1982 models (sic) cars have a 4 watt indicator lamp, however the larger socket cannot be inserted in the instrument clusters of older models."

Which is why you can't just put in the new, higher current, lower resistance, higher wattage bulb.

I like the idea of putting a switch on the fan belt, if the possibility of its failure worries you. I've never had a problem with one on the track or street, but have seen it happen.

An alternative would be to use an electronic gizmo to measure your overall system voltage, so that, when it drops below the minimum level it should be with the alternator working, it turns on the big warning light you have installed on top of your dash (with a race car you have more options to locate things, don't you). This should be a bit lighter and have less potential to cause mischief than a mechanical belt sensor. I bet Doyle could design a simple circuit like this in his sleep. You can purchase voltage measurers you plug into the cigarette lighter for under $20 which have red, yellow, and green LEDs to show voltage level, so one could start with that and fire a 12V relay instead of the red LED?

I favor the digital voltmeters which plug into the cigarette lighter. Yes, I'm not checking it when on the track, but if a warning light comes on (as they are wont to do when you are idling on the grid on a hot day), I can check it. Same as with the oil pressure light - it comes on, and you can look at the pressure gauge and promptly know if you have a problem with pressure or not.