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No the pump never starts. The control box has a little speed controller in it. It looks just like the ones you see in the toy RC cars or planes. When you start those up it takes a bit for it to load up the capacitors I think.
Let us know how this works for you, I have a new one in the tool box for my trans cooler that I need to wire up now that you mention it.
I took my switch apart and learned quite a bit with my multimeter. The switches are set up together with their respective relays to do certain things. You can't just take one of those switches and use it in just any application and expect it to work like OEM without the proper matching relay wired up for the desired task. My defroster switch connects a circuit when I press the button left or right but it releases that circuit as soon as I let go of the button. The relay takes that brief electrical signal and flips the defrosters on or off. The relay also returns voltage to the light in the switch to indicate if it is on or off. So for your application you could use that switch but you would need to find a relay that switches on and off and has the return wiring to flip on the light. I think the defroster relay has a bunch of stuff to progressively heat the window and then turn itself off at a certain point, so that wouldn't be a good choice. The door lock relay might work. For myself I'm just going to add the switch to my existing pump controller relay and just hold the button down to get my pump to spin.
We have it set up that when the ignition turns ON, the fuel pump runs for a brief moment instantly priming the system. When the key is rotated to start, the engine fires right away. Additionally, the fuel controller is programmed to send a signal to the fuel pump to run as soon as engine rpm > 10. We are using a Motec DHB fuel pump controller.
I was just thinking something similar - why couldn't you wire the pump to 'key insertion' so it primes before the ignition is turned?
There is some type of circuit associated with the key going in the socket - the odo/mileage comes up when key inserted.
I am by far not the guy to talk to about things electrical, but I suspect there is some kind of electrical interface that acknowledges the key being inserted.
The key in switch signal comes out of the ignition switch and is routed to fuse E1, then it goes to a bunch of equipment: audio system, instrument cluster, alarm, etc. It would be live the whole time the key is in the switch whether it's turned or not.
The key in switch signal comes out of the ignition switch and is routed to fuse E1, then it goes to a bunch of equipment: audio system, instrument cluster, alarm, etc. It would be live the whole time the key is in the switch whether it's turned or not.
Ok I'll snap some pictures of what I'm about to try and you can tell me if I'm an idiot or not.
I splice into the hot + wire on one of the other switches and use that as my power source for the new switch (picture 1 red wire with black stripe). This will plug into the horizontal tab on the new switch (picture 2). The two vertical tabs below the horizontal tab connects with the + power when I press the switch left or right. I then run the on side wire to the red low amp wire on the relay and the off side to the black wire on the relay (pictue 3). This should trip my relay on or off when I press the button. The red high amp wire comes directly off of the battery to the pump controller. The on off wires to the relay come from the pump controller. This should override that on/off signal when needed. Does that make sense? Edit: I just tested my pump controller relay and it stays on when the low voltage is always hot. So I will have to hold down the button to make the pump turn on and the off side won't work.
Last edited by Bernard IV; 10-22-2020 at 08:01 PM.
As mentioned/discovered, the porsche dash switches are all momentary switches and when used by Porsche, all latching functions are done downstream (Body Control Module)... They are perfect for using when wiring to something like a garage door opener where a pulse is fine, but if you want something to stay on, you'll need a latching relay that is controlled by the switch.
https://www.the12volt.com/ has wiring diagrams for all kinds of relay functions, but this one might work... Ground pulse from switch to latch relay, stays on till power or ground is interrupted (like ignition switched off), and uses standard high current automotive relays. Ground pulse also means you don't have to tap in to any other switches, just to any ground.
Probably want to use another (third) relay with switched power as the relay trigger (low current), and your high current wire directly to the battery through the relay to feed into the "fused 12V" portion of the circuit.
This wound up working out well for me. I used a defroster switch installed into the blank switch spot and tapped into the hot wire on the PSM switch. I ran it to the relay on the fuel pump. I hold the switch down before I start the car and all is well. It does light up the PSM button LED when I do this but does not flip that switch.
10-21-2020, 01:46 AM
