RS Blog 22 - Wires and more
Actually this post is entirely about wires and the headache of building a custom loom…
Step 1
Try to save/use the factory harness only to become ever more frustrated by fuses and butt splices. While installing my chassis harness I accidentally pulled apart at least three connections. That is three connections I found, let alone maybe others hidden under the black wrapping. The more and more I looked at the harness it was clear it was just going to frustrate me as I tried to integrate the PDM setup from Haltech. Relays and fuses were just not needed along with control switches that didn’t need to be stuck in their analog ways.
Eventually I tossed the entire harness, just keeping a few terminations for reference. Basically only the front and rear connectors to the clam shells for lighting. I’ll be re-pining to my fresh new wires so there is not any splices.
Step 2
Identify all the amazing and cool things you want to do with switches, buttons, sensors, engine and lights. Identify all the inputs and outputs they all require to compile a master list of stuff that must find a home.
Step 3
Realize you don’t actually need to control the world and you’re building a track toy that needs to be safe…ish. Pare it down to the essentials:
…wheel speed sensors for each corner, shock position sensors, clam and door open/closed status, boost control on your naturally aspirated LS7, EGT sensors, flex fuel sensor, cruise control. Ya know the bare minimum for your home build super car. Oh and the normal stuff like injector, ignition and lights…
Step 4, 5, 6
Order an LS DBW harness from Haltech, receive an LS non-DBW harness and only realise it after you open the bag of wires and wonder where the DBW connector got off to.
Send it back and get the correct LS DBW harness only to realize it is configured for your typical front engine muscle car and thus wire lengths will never work for the mid-engine layout of Ultima.
Send it back…. to order their universal 5 meter harness and get to figuring out every single engine control wire.
Step 7
Start working on a wiring diagram while starting to mock up wires on the chassis in hopes you’ll have a diagram to match your final car harness. Get distracted with working on the actual harness and reminder yourself to go back later and clean up the electronic version to match reality.
It is partially a Jaaaaag!
For the rear brake lines, Ultima provides a brass four way connector to allow connecting the brake pressure switch. As I’m using brake pressure sensors for front and rear I thought it would be useful to get another to replace front 3-way junction. Upon searching I found it is a part for an E-type Jaguar!?!?! Fun times. So now I can say for better or worse my Ultima has Jaaaag parts.
Wiring Design Philosophy
While this is my first harness from scratch, it isn’t the first time I have dealt with a harness or modified one to suit different needs. I’ve spliced engine and chassis harnesses together, parsed them down to minimize weight and even just done mild additions for extra accessories. Every time I work with car wiring I have some primary goals.
Minimize wiring length, avoid looping, etc.
Minimize splicing when possible as they are failure points
Ensure wires stay away from any mechanical vibrations or heat sources. These both deteriorate wire over time.
Keep everything uniquely color coded. Greatly helps with wire tracing/troubleshooting.
With these in mind I mounted my PD16 on the driver side with intent to manage chassis power similar to factory. And conversely mounted the ECU on passenger side to allow for control signals balanced on opposite side. Another distinction I made was eliminating any duplicate paths for wires…. so anything from the passenger side to drivers side for say control inputs, doesn’t cross the wiring from PD16.
I also split primary power between left and right sides of chassis, left side for both radiator fans, nose lift pump and left fuel pump. While the Nexus on right side manages the right fuel pump, AC condensor fan and engine power (injectors and ignition).
A few final notes….
As I work through wiring I do change my mind with routing and connections. It took a month or so of back and forth to decide on this layout. After which I’ve been working through the exact paths for each bundle of wires. Using cleco’s and zip-ties to mount and move things as I adjust. Don’t think you’ll figure out the perfect harness the first time, nor will it end up exactly perfect.
My next steps will be to order loom for each bundle/routing, zip-tie each junction point to ensure they don’t move, remove the whole harness and loom/heat shrink it into its final configuration then re-install into the chassis with stainless loop clamps and rivets. Some parts will likely be left un-loomed until I get engine install to have best fit.
