911SC 3.6 conversion fuel pump wiring mystery - Patrick motorsports harness

[s14kev]

I have an 83 911SC with a 993 varioram engine. Conversion was done before I purchased it and it has the Patrick motorsports DME conversion harness. The fuel pump runs all the time with ignition on even without the engine running. It looks like the shop that did the conversion did not wire the harness per PMS instructions. According to PMS the 16ga red wire is supposed to go to the fuel pump terminal to run the fuel pump which is the 6th fuse from the left on my panel (wire marked with white tape). In the photo below, I have the PMS 16Ga wire marked with red tape and it runs to the 9th fuse which supplies the cig lighter/washer. The black wire which I've marked with blue tape is supposed to go to switched 12V but the shop has connected it to the bottom of fuse 10. It was a reputable shop that did the conversion and I'm guessing there is a reason why they did this however any clues for this reason?

I also don't quite understand the small 16ga wire to run the fuel pump in the PMS conversion harness. The original fuel pump wiring is 2.5mm going into fuse 6 and 1.5mm coming out of fuse 6. 16ga is equivalent to 1.3mm which doesn't quite seem sufficient to supply the amp draw of the fuel pump. What am I missing?

[spuggy]

Originally Posted by s14kev

I also don't quite understand the small 16ga wire to run the fuel pump in the PMS conversion harness. The original fuel pump wiring is 2.5mm going into fuse 6 and 1.5mm coming out of fuse 6. 16ga is equivalent to 1.3mm which doesn't quite seem sufficient to supply the amp draw of the fuel pump. What am I missing?

I know squat about 3.5 conversions generally, but I'm going to SWAG that in the PMS conversion diagram, that 16ga wire is used to switch/trigger the control side of the fuel pump relay and doesn't carry current for the fuel pump itself at all.

Which, as you say, would be far more (like 10A or more) than you'd want going down that wire.

[s14kev]

Well I just realized that fuses 6, 7, 8 and 9 are all interconnected at the top power feed so connecting the red 16Ga wire to run the fuel pump to the top of the fuse 9 is no different to connecting it to the top of fuse 6.

It also learned that 911SC's have a fuel pump that runs all the time when ignition is on even when the engine is not running unlike the 993 DME which only runs the pump when the engine is running. The PMS instructions say to disconnect the wire running to the fuel pump fuse and replace it with the 16Ga from the conversion harness. I'm guessing the original wire to run the fuel pump is still connected. Need to work out how to find this in the jumble of wiring left over since this car also has a classic retrofit fuse panel.

I pulled the PMS conversion harness to tidy it up since it uses sketchy electrical tape to bind it. I was going to sleeve it in the correct Porsche style black PVC tube. I did find this power transformer taped midway in the conversion harness spliced into the yellow wire that runs the tachometer. Any clues why someone put this there?

[wildcat077]

I would reach out to Patrick Motorsports and ask them for their advice ... i dropped a 95 3.6 in my 89 and i used the Patrick hardware and wiring kit and the installation was pretty straightforwad as per their instructions.
Somebody prior to you seems to have added some home made wiring that wasn't necessarily part of the PMS wiring kit!

I also modified my fuse panel, similar to yours ...

[rumlyne]

your car probably now has a DME relay somewhere.
Find the computer and see if there is not a relay within a
few inches of it.
I have a SC with a V-RAM as well but mine is an instant-g
conversion.

[3rd_gear_Ted]

Originally Posted by s14kev

Well I just realized that fuses 6, 7, 8 and 9 are all interconnected at the top power feed so connecting the red 16Ga wire to run the fuel pump to the top of the fuse 9 is no different to connecting it to the top of fuse 6.

It also learned that 911SC's have a fuel pump that runs all the time when ignition is on even when the engine is not running unlike the 993 DME which only runs the pump when the engine is running. The PMS instructions say to disconnect the wire running to the fuel pump fuse and replace it with the 16Ga from the conversion harness. I'm guessing the original wire to run the fuel pump is still connected. Need to work out how to find this in the jumble of wiring left over since this car also has a classic retrofit fuse panel.

I pulled the PMS conversion harness to tidy it up since it uses sketchy electrical tape to bind it. I was going to sleeve it in the correct Porsche style black PVC tube. I did find this power transformer taped midway in the conversion harness spliced into the yellow wire that runs the tachometer. Any clues why someone put this there?

Maybe a source for the Tach reference voltage

[zelrik911]

I agree with 3rd_gear_Ted
I have a 3.6 conversion and this looks like my Tach output solution. My wiring is Instant G.

[s14kev]

I traced the PMS wiring harness. The 16ga wire on the PMS harness connects to pin 87b of the fuel pump relay which I understand powers the fuel pump. The stock wiring to the fuel pump is 2.5mm into the 25A fuse and 1.5mm out of the 25A fuse. 16Ga is 1.31mm which is much smaller. The fuel pump draws ~7A but this can go up as they wear. PMS harness instructions are below. Any thoughts on why the PMS harness only runs a 16ga fuel pump wire?