Got the USM (Universal Sensor Module) sorted. The USM is a four channel add-on to the Racepack digital dash allowing the addition of any sensors you want. Black box in the pic below:
The USM is why I finally took the plunge on a digital display. The original plan had been to add at least two more Accutech SMI gauges to the two I already had in the car so I could keep track of temperatures of all the various important bits. I realized I was heading down a path to having a very busy interior with a lot of things to try to keep an eye on.
The digital dash simplifies everything into one place where I can program warnings for each input and leave the dash to monitor things while I just drive. The dash pulls most of the engine vitals info I need right through the OBDII but the USM makes it possible to add the extra sensors I wanted and simplifies the wiring by transferring everything to the display via one V-net cable.
The sensors are already installed in their various locations, documented earlier in this thread. Now, on to wiring up the sensors to the USM. Here I’m using milspec /32 wire same as previously, but this time in 22ga twisted pairs. The twisting is a method of shielding the signal from interference. Frankly, you don’t need it for these types of sensor’s signals but here I used it because it helps keep things tidy:
Wiring within the USM box. The USM has a strain relief feature on the inlets which is a nice touch; tighten the outer nut and it clamps down on the wire to secure it in place:
The finished USM harness:
Mounting the box was done on the top/rear of the engine via a pair of simple brackets. Yes it’s tight back there. This is mounted to the engine so that all the sensor wiring can stay with the motor when it’s removed, just disconnect the single V-net cable connector:
With the box mounted we just need to run the V-net cable to the display. This could be done with one long cable that would need to pass through the firewall, or a bit cleaner version here that involves two shorter cables and a bulkhead connector:
Tidy!
The remaining wiring to be done was to tie in where necessary on the GM wiring harness. Most of this was coming through the firewall from the chassis harness – things like ignition switch, start button, lights, fan, drive by wire throttle, OBDII, etc.
I blasted through this and forgot to take all but one picture – V8R advised that the throttle pedal signal is very sensitive to interference, so for this I ran a 6-wire shielded cable on both the chassis and engine side:
The rest was just patching stuff into the existing engine harness. The stuff I added is all on par with what I did on the chassis side, but I’d love to re-do the entire engine harness in the future so that it is all up to higher standards. However, for now it’s a good working harness and this thing needs to be running!
All of the wiring interface from chassis to engine converges in the rear right corner of the engine bay. Everything is set up to disconnect from the chassis quickly/simply and comes out intact with the engine. There’s only four total things to disconnect, all located here: main bulkhead connector, v-net connector, engine ground and one M6 bolt that holds the fuse/relay plate to the firewall. Not trying to hide wires or tuck anything away, the goal here is easily accessible and quickly removable:
