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Discussion Starter · #1 · (Edited)
A bit of context, I have a BEAMS-powered endurance racecar. It's done a few 15-hour races, and mostly survived. The main target for it is the NASA 25 hours of Thunderhill, maybe in 2023. On a good day, it looks something like this:


For the last year or so, it's had intermittent electrical problems. Annoying electrical problems that led to the ECU and fuel pump occasionally losing power for a split second while on track (it's especially scary once you're side-by-side with another car mid-corner, fighting for position). We did lots of relay swapping / bypassing / chasing bad wires in the harness / etc. Eventually, all the shady last-minute fixes in the pits caught up to us, one of our bypasses ended up shorting main ECU power mid-race, and we ended up losing another engine. Not great.

So, I decided to take the car offline for a few months and do a full from-the-ground-up rewire. And "while I'm there", make it easier to observe / debug / and generally mess around with. I was mostly excited about swapping all the relays with a PDM (modern technology from the 1950s! transistors!), but going that far, it made little sense to keep the stock ECU -- it's a giant black box after all. All in all, that means, standalone ECU, PDM, a solid-state battery isolator (instead of a mechanical kill switch), and a CAN keyboard to control everything (just two wires for all switches!). And of course, shiny new custom harnesses to connect all that -- hopefully in a reliable way. I had an ECUMaster Black from some previous plans -- the rest of the stuff is also from their line of products (PMU16, etc).

I've gotten to a point with the design where I think I have most of the basics figured out, and I'm comfortable sharing. The attached files have a basic functional diagram of the wiring, a tally of rough total power consumption for the PDM, and some notes for the first section of the harness I'll start to build now (firewall to engine bay). Notes / comments / critique more than welcome. There's still a couple of things I need to figure out -- how to drive the wipers motor, how much power the cooling fans actually draw, but these should be pretty simple.

Depending on the answers of these, there might be 1-2 PDM output ports left for switching future things, like night lights. But generally, even in a basic stripped down racecar like mine, 16 PDM outputs run out pretty fast, and I had to make some compromises (like, would've been nice to put the data logger on a separate line to restart mid-race -- AiM stuff is notoriously prone to freezing).

I went back and forth quite a few times on the physical placement of things. For a while, I was set on putting everything in the trunk (battery, PDM, ECU) to minimize the really thick wiring between the alternator / starter / battery / PDM. But then I remembered how much of a pain it is to run wires between the trunk and the cabin -- and the cabin accessories (cameras, dataloggers, night lights, etc) are the thing most likely to change over time. So, the final placement plan is much closer to stock -- the battery stays in the frunk, along with the solid state isolator and the power distribution module. This way, wiring between the PDM and all the cabin stuff is pretty easy to change. The main difference is the ECU is also in the cabin -- in the back, on the firewall. There's a single bulkhead connector in the firewall that leads to the engine bay, for all the wiring that needs to go there (minus the big alternator and starter wires). There's only a couple of things left the trunk (stoplights, taillights, accusump) and their wiring can be set in stone. All fuseboxes and relays are gone.

I'm excited -- this is definitely a big project (not to mention, still need to rebuild an engine, and tune it with the standalone), but should be pretty good (and hopefully bulletproof) once it's done.
 

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Yeah, there's nothing worse than trying tho fix botched wiring. When I bought my car, there was no radio, just a big hole in ghe dash, and lots of mystery wiring. The factory subs were gone as well.
Good luck with your project, it's great to see our cars ripping around a racetrack.
 

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Discussion Starter · #3 ·
Yeah, it's ironic -- in my day job I'm most often arguing against junior engineers wanting to redo everything from scratch. And now I'm doing exactly .... that.

Anyway, between other projects, got to "bench" test the PDM with a tiny test harness. It drove some cooling fans just fine, and the CAN bus configuration for the device was ok. Importantly, it also told me the Mishimoto fans draw 7 A each in steady state, and 15 A of inrush. With PWM "soft start", that goes down to 9 A inrush current for each fan. Now it's time to just take down some physical measurements and start laying down the harness(-es).

 

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Discussion Starter · #4 · (Edited)
I was having so much fun making harnesses, I forgot I started this thread.

The basic design hasn't changed too much -- cleaned up some connectors, added an expansion here and there (like for an external MAP sensor), finally figured out how to drive the wipers motor. Small stuff, but needs to be done.

Made lots of progress on the physical layout of the harness -- where to put the splices and the branch points in the harness, what boots to use on each branch, things like that. After watching too many HP Academy wiring videos, I've been using open-barrel splices and wrapping them in Raychem SCL for insulation and strain relief -- that stuff is awesome. Once the engine bay harness is set in stone, I'll wrap it with Raychem DR-25 for some extra protection from all the nastiness that happens in there. Here's that harness, still unterminated, slowly growing in girth (it's even thiccer now!):





When I got to the ECU patch harness on the other side of the firewall, I realized I'd made some mistakes. I've been using 20 AWG TXL wiring for the low-current stuff. It's already a bit overkill for motrosports, but I don't like crimping 22 AWG (let alone 24), so 20 it is. I hadn't checked the ECU connectors too closely and, as it turns out, they'd put a decent number of low-current things (like signal grounds) on Very Big pins, where I couldn't even fit my bulky 20-gauge wire in a reliable way, without some shady crimping. Sigh. Lots of rearranging and repining later, I found an arrangement that worked, with 16-gauge wire and no need to replace a bunch of expensive Deutsch connectors I'd already bought. But still, talk about overkill -- AWG 16 for a few hundred mA...

Anyway, eventually got that side of the firewall done too, at least enough for a test run:


That's about as much as I can do on the bench, without bricking the car for the next who-knows-how-long.
Next up, test fit everything again, cut to length, and terminate all the engine connectors. Then it gets fun -- rip out all the old wiring off the car and pray it's gonna work...
 

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