I need a switched 12V power source in the engine compartment for PLX sensor modules

[RichPugh]

So... I need a good 12V source in the engine compartment, ideally on the drivers side, in or near the sealed relay/connection box. Short of running a power wire from the battery back into the engine bay, what are my options?

FYI, it's a 96 993. I've ditched the secondary air system and the cruise control so I thought to use something there. I am also ditching all of the OBD2 functions as the stock Bosch Motronic DME is being swapped out for a custom ECU.

The big 40A fuse in the drivers side relay/connections box for the secondary air pump was my original idea but it's not switched. It has power all the time. I did find switched power from my old cruise control harness but it's only providing 11.7-12.7V depending on RPM range. Strange considering the 40A fuse metered like 12.6-13.4V... ??

I need to power 3 PLX sensor modules. AFR, Boost/Vac and Fluid temp modules. I can tuck 2 into the relay/fuse/connections box on the drivers side and tuck the 3rd (probably the boost/vac module) just in front of it.

Inside the cabin is where the gauge module needs to be so I'll get power up there from somewhere.

Any recommendations? Thanks!

[bpu699]

I think most folks put the plx modules under the passenger seat. That's what I did. Switched power is off the radio supply, ground to any screw under the seat. Works great.

Bo

[RichPugh]

PLX suggested putting the sensor modules in the engine compartment and only the gauge module in the cabin. Seems like the most logical considering this way, the only wire(s) that need to go inside the cabin from the engine compartment is the signal cable for the gauge module (a standard 3.5mm AUX type cable). If all the sensor modules were inside the cabin, I would have to run a boost/vacuum line from the engine bay to Boost/Vac module, 2 temp sensor wires (from the oil temp sensor and intercooler liquid fluid temp sensor, in my case) from the engine bay to Fluid Temp module AND a wideband 0-5v signal wire from engine bay to the AFR module. Thats 3 separate wires and a boost/vacuum line as opposed to one 3.5mm aux type cable.

I went back out and pinned out the rear window defogger relay socket. Position 15 is switched 12V and 31 is Ground. I think I'm good. 2 modules fit snug in the relay box over there and I can keep one outside tucked away. I'll just drill a small hole in the bottom of the box and use a rubber grommet for the necessary wires.

But I will probably use the 12v switched inside from the radio for the gauge module under the passenger seat.

Thanks for the reply.