Help finding a specific switched live

I am looking for a switched live, however I want it only to be live when the engine is running and not when the ignition is on, does such a live exist? Ideally located at the front/frunk of the car / footwell fuse box and not the engine bay. Thanks

I'm pretty sure what you want does not exist. Think about it from the ignition switch. You have OFF, RUN and START positions. OFF cuts power to most of the electrical systems. RUN position powers up all of the electrical systems and START powers up the starting circuits to only start the motor, then back to RUN. So where are you going to find a circuit "when the engine is running and not when the ignition is on?" The ignition has to be on for the engine to run....

I was hoping for something alternator related, you only get an output when the engine is running, but I agree that nothing may exist, hence the question. - Worst case I will use a switched live, but wanted to explore if the perfect scenario existed.

May I ask what you are trying to do?

Electric Power Steering Pump, however I run a small battery so ideally I do not want the load of the pump coming on-line until the engine has started. Worst case I will use a switched live, however ideally I do not want the pump running when the ignition is on and engine not running.

I assume you track the car, it this is a weight thing? I think it would have to be on a switch to achieve the scenario you are looking for?

" I think it would have to be on a switch to achieve the scenario you are looking for?" ^^^ Bingo!!!

Removing the hydraulic power steering pump has many benefits, weight is not really one of them as the kit you add, weights the same as what you remove, I see reliability as the biggest benefit. The hydraulic pump is mounted in the engine bay, its belt driven via the engine, pipes then run the length of the car to steering rack at the front of the car. By removing the pump from the engine bay you benefit from a very small bhp gain as there is no parasitic loss to the pump, the Power steering fluid is not being heated by the high temps in the engine bay and you remove all of the pipe work that runs the length of the car and is prone to developing leaks. The steering rack also can develop leaks that yo may not immediately notice, the hydraulic pump then runs dry and can seize, not only destroying itself, but all potentially causing issues for all of the other items that are connected to the same belt. The rack is capable of running with no fluid in it, not ideal but it can get you home, with an electric pump it if fails it only takes itself down, and should you spot a leak on the rack you can also isolate the electrical pump. - 996 RSR and later, 997 on, cup cars all run electric power steering pumps, the pump and associated parts are all Porsche parts. Yes the car is a track car, however its driven to the circuit, so slightly different from an RSR your switch solution would work, you start the car, hit the switch and the electric pump fires up, however prior to considering this, or the switched live, I would like to seek an integrated solution if possible.

I think you need to take a look at tapping into something in the power distribution box. It is located behind the carpet on the firewall in the passenger footwell. Those are 50/80 amp fusible links. Maybe the power window since that would not be used much in a track environment. Tap into that and put in a dash switch for the electric power steering pump.

I wonder if u can use the field wire on the alt to triger a relay or even better use the fuel pump trigger to fire the relay. Then it may prime but it should shut down if the motors not running.

Thanks for the diagram - There is some information out there that suggests that Terminal 61 can be used, this is the 'Alternator C harging light circuit control' however I do not know where this is located, or how to identify, I am going to check the distribution box you mention. However if there is anyone clever out there wants to spoon feed me the info, please do!

depending on the pump you are using there is a built-in control circuit that will operate off the alt light. the pump would have big + and -, and two controls; one w constant + control voltage to power the control circuit, and another that turns pump off if it sees control voltage (ie from alt light or any other system that activates when ignition on but engine not running).i think. if you can't find the alt signal then you have a switch but for oem look note that porsche switches are momentary contact so you will need a locking relay to provide a constant signal. hard to find automotive locking relays; the best i have been able to find is a hella unit for mercedes glow plugs. i can get part # if you like.

RK, I hoped you would chime in, I have searched your previous threads but cannot find where to wire the control cable in. I am using the TRW cup pump. Thick red to the battery, 80amp fuse, thick brown to ground. - Then we have the thin black & thin blue & white. The thin black is a switched live, no problem, its the thin blue & white that I am struggling with. - If this is connected to the dash battery/alternator warning light will the pump run when the engine is running? For my reference, if I splice together the thin black, with the blue & white, and connect to a switched live, would I be right in assuming it would work but the pump would then operate with the ignition and not the engine?

The reason I suggested the power distribution box is that you will need not only the 12V but wires with a size big enough to handle the motor amps. Do you know how many amps are needed to run the pump?

not sure? my pump had three control wires - the third was an output to the dme for trouble light. i think run a test; put your switched control power on the black, and see what it takes to make the pump spin on the striped - power or no power.

Quotes source post: 15959064

big power comes right off the battery, and gnd goes to chassis.

Your less than 3' from the battery in the frunk... The switch you might want to use is called Hobbs switch ,, its used in airplanes to track the run time on the engine. There is both a hobbs switch and a hobbs meter,, the meter measures the runtime the switch tells it when, its basically the idiot light switch off a car that closes with pressure, just way more reliable. Another option would be the fan power,, IIRC the fans stop while cranking. The electric power pump "should" be a demand pump, it should not be running unless your turning the wheels. (I dont know this it just seems logical? )

you can tap into the alt wire at the abs unit in the frunk .From memory it is a thin blue wire .However I would check the wiring diagram to verify and recommend an inline fuse .

What year do u have? Some things change after 99. I have been digging around in the bentley book trying to figure this one out. The wire off the alt is deff blue. It runs up to the cluster and to the abs pin 10 on the 1999 cars as far as i can tell. On the 2002 it looks like it goes to pin a22 on the psm. Im not a 100% sure if this 12v power or a ground trip. U will have to test it. I figure i should look this up as i will be going to the electric pump when i do my ls swap.