Im getting close to having the car ready to run. Engine is rebuilt, just waiting on an LIM to be able to put it in.

My MS1V3 is built and passed all tests with Stim. I have updated the firmware and easytherm for Mazda temp sensor.

Now, my car did not come with any type of engine harness, the PO sold it for whatever reasons. I have some of the clips for certain things (680 CC injectors, CAS, TPS, ect ect) and waiting on a few others.

So with that bit of background on MY car, Id like to know who has built from scratch thier own engine harness? When you did it, did you build an new circuit from the ignition switch to all main fuse, fuel pump fuse, and the MS?

Im looking at REnns thread with his build up and subsiquent diagram, but find myself a tad confused with the leaving out of the Leading and Trailing coil packs. I believe that the 12v side of the coils are on the actual Battery harness? I have not looked too much into the factory diagrams for under hood because I was busy cleaning up the mess of wiring the PO left me with in the passenger compartment.

IF anyone has any input or advice, Id greatly appriciate it.

 

I usually trash the "right" side harness, I just don't feel comfortable using that brittle stuff. Typically, I do salvage the windshield wiper motor plug and wire to the dash harness(it isn't as brittle as stuff over the motor). I also have run a new line from the ignition switch to the relays(nice line to insert a kill switch as well).

The coils do get their power from the "left" side harness. You can "tap" your coil grounds into the left harness, or if you don't have any harness whatsoever you can run 12v switched to the coils, and run your 3 coil lines from the ms directly to the coils.

If you want to drive the factory tach, run a line from the trailing coil tach out thru the firewall to the factory gauge cluster harness. If you want the factory temp gauge, I typically run a line from the rear housing temp sensor thru the firewall to the gauge harness as well.

 

Could you not use the dash plugs to serve as power, ground for megasquirt and use the connectors to go to the tach water temp etc. Then use a new harness to go to the control systems form the megasquirt? Why do you have to run new wires for those systems?

 

I'm in the process of installing a new harness in my SA. I'll have to snap a few shots. In the meantime, here's a few random thoughts:

I've built a few from scratch, and it's a PITA to do properly unless you have access to proper crimping tools, connectors, etc. Typical hardware store tools are marginal for critical connections on a vibrating engine IMO.

You may want to start with a pre-made harness like this:
http://www.glensgarage.com/catalog/u...port-p-77.html

Spend lots of time laying out the harness, routing, etc. Make sure all pigtails are relaxed when installed, not tight. You don't want connections strained with engine movement. A bit of spare length also allows some routing flexibility. Think about component/harness removal as well. You want to be sure all components can be removed without snipping any wires.

Make use of heat shrink tubing and proper harness tape as well. Resist the temptation to use std black electrical tape. It'll look nice at first, but will become a sticky mess over time.

For injector connectors, I use ones scavenged from Volvo's at the wreckers. They fit the std rectangular plug low-z injectors, and have a quick-release retaining clip, rather than that miserable little spring clip that's normally used on our cars.

With this new build for my SA, I made up a mounting plate that carries an FC fuse box, 4 relays (e-fan, ignition, fuel pump, spare), and the FC leading and trailing coil. This is likely beyond what you need to do if the existing vehicle systems are in place, but works very nicely when upgrading an older carb'd vehicle.

Document everything well so years down the road your or the next owner has a chance of figuring out what you did.

 

So lets say you want to replace just the passanger side wire harness. What do you have to do to retain the inputs for the water temp, tach ETC. also can you use these plugs to give a switched safe voltage as well as retain the use of the main relay. The diagram given in the FSM does not reliably explain these items to me, prehaps i have an S5 version.

 

After seeing efini's post I was expecting the worst (I think he has a hell of a mess) ...

Renns > Great info there ... Thanks for the volvo tip ... those sound like nice injector plugs.

Grendel>

I take myself back on the tach(I think it might work ok, I just had a car w/ hacked stuff, and can't remember to be sure). See below for gauge water temp.

You certainly can tap into the ecu plugs from the left side harness for power ... I wouldn't use the ground for ms though.

I am sure you could tap into things in the left side harness ... just use the FSM for reference and continuity check lines to be sure(I never wanted to open up the left harness, prolly because I just dislike working upside down looking into the dash).

For losing the right side harness, off the top of my head the coolant gauge signal is part of it, so you could scavenge it out and re-use(iirc it goes w/ the wiper motor plug). The wiper motor stuff(which I do re-use), and I presume the cruise control/sub zero stuff(never really had to deal with that yet)

In the end there are numerous ways you can accomplish this, do what makes life easy for you ...

 

Renns. thanks much for the input. I have access to pro auto electrical repair tools. Spent close to a grand on all my OTC ****. Im not a big fan of strip and crimp. I solder all my repairs and connections with heat shrink to cover it. Do it right the first time, I always say.

As far as using a prebuilt harness, I have looked at it and just wondering if it needs any modifications at the DB37 to work correctly? Input there? If I have the right info for it, Im gonna go that route.

T2GTUS, yes it is a mess. ALL HARNESS's were stripped out of the car. I got most of the passenger compartment redone, but the engine bay is becoming a pain. Im sure once I get the engine and coils and other **** in, IT will clear itself up better.

What wires on the back of the gauge cluster do I tap for the TACH and the Temp? What wires do I go from on the coil to to drive the TACH?

 

Ohhh. T2GTUS, thanks to you too for your input. Im like a sponge with this ****. Gotta soak up what I can about this and the 7 in general.

 

hmm I will have to look ... do you at least have the plugs for the cluster?

 

I got all wiring in the car except for an engine harness. The cluster is already plugged up in the dash but the dash is not installed. I took it back out to have acceess to the Left harness so I could wire up the rest of this stuff to the rear of the car.

 

If you go the missing-tooth CAS mod route, that harness will work as-is. If you go stock CAS route, you need another spare pin to bring in the second VR signal. There's probably still an unused one on that harness somewhere. Worst case you'd have to add another lead to the harness.

 

Sweet. Im goin with Missing tooth. Now to finish gettin the plugs I need for the engine side. Gonna pick that up this weekend and hopefully get the damn car to start in another week.