Best place to tap +5V in engine bay?
 

Looking to add an aftermarket 3-wire sensor and I need +5V in the engine bay. What's the cleanest place to draw power from?

I've searched, but "5V" is too short to be searchable and "+5V" has no useful hits

Thanks

$lacker,

Good luck finding a +5V power source in the engine bay. Have you already sifted through the wiring diagram manual? Nearly all of the FD's power circuits utilize +12V. I haven't seen anything as I perused the schematics. You may have better luck finding a sensor that uses +12V. Speaking of which, what 3-wire sensor are you attempting to use?

Cheers,
George

An auxiliary 12v to 5v converter might be another option for you.

I'm looking at using an AEM 30-2131-150 oil pressure sensor in place of the stock one - I've got an Adaptronic ECU and AEM CD-7 digital dash.
If there's no engine bay 5V source I'll need to draw from the cabin, which isn't terrible, just slightly inconvenient

A lot of the factory sensors use a 5V supply. Throttle position, water temp, and air temp are examples. Look through the pinout of the Adaptronic, find the +5V supply wire's pin, and trace it through the harness. It should branch out and go to the different sensors that use it.

If you're somewhat handy with a soldering iron you could use a DC to DC converter to make 5v. Here is a Traco TMR 3-1211E on Mouser Electronics that would work well enough to power your gauge. It will take 9-18vdc and convert it to 5vdc.

Thank you
Looks like the MAP sensor wiring will be the easiest place to tap into. I can get +5V from the BR/W wire and signal ground from the B/LG wire. The other wire is the signal (G/Y).

I would be hesitant to tap 5v off another circuit - as stated, most of the 5v supplies are for sensors, like the TPS or MAP sensor. If you are drawing current from that supply there is a possibility that it could reduce the input voltage on that sensor and cause a faulty reading. I may be overthinking it though :).

The fuel temp sensor uses a 5v input, if you've eliminated that you could tie into that wire.

Dale

I feel like that would be an issue if I were using it to run an electric motor or heater or something, but I don't expect to have a problem running an additional 5V sensor off the 5V sensor power (or running the ground into the sensor ground).
It comes from ECU pin 3I, which is the 5V feed that is designed for that purpose.

Makes sense - I think I was over thinking it :).

Sensors draw a tiny amount of amperage. If you do tap into a primary sensor (especially the MAP sensor) I would make certain that the quality of that electrical connection is top notch. If the MAP sensor loses input (due to a break in the 5v wire) that would be a real pain.

I think you're on the right track, I'm mainly commenting for anyone else reading this thread :).

Dale

I should be able to plug/unplug the extra sensors to see if they affect the MAP sensor at least, but hopefully there are no issues

Here is the relevant circuit

You're over thinking it at this point, in my opinion. If you're running a new ECU designed to have a fairly massive amount of sensors compared to stock you can tap off of almost any one, just make sure its clean. ECUs tend to have only 1 or 2 pins supplying 5v and the same for sensor grounds.