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FC S4 Wiring, what's safe to remove

Old 12-11-15 | 09:00 AM
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cegan09's Avatar
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From: NH
Question FC S4 Wiring, what's safe to remove

Greetings. Hopefully this is the right place for this, I didn't see an electrical specific section.

I have the drivetrain and wiring that I pulled from a 1988 RX7 Convertible. I'm starting a project putting these into an E36 chassis for the purposes of running in the 24 Hours of Lemons. The biggest first hurdle that I'm tackling is wiring. The end goal is to have a barebones mazda harness that runs the engine like stock, displays gauges, and that's basically it. The E36 harness will control things like lights, windows, HVAC, etc.

So with that out of the way, I've started digging into wiring. In fact I've spent the last 5 nights pouring over wiring diagrams, confirming what I have, learning how it works, and starting to pull things out. Everything radio related is gone. HVAC is coming out. Any connector for exterior lights has been pulled back to the firewall grommet. However I have a few questions about other items and what I might be able to remove.

1. Theft Deterrent Control Module
From what I've read I think I can simply pull this box with no ill effects on the function of the car. I just want to confirm that. Also, if I take that a step further and start pulling the individual wires from the harness, are there any that really should be left in place? I think I can pull most of them since they go to things like lock cylinder switches, hood switches, door switches, etc. However there is one wire that runs to the starter cut relay that I haven't yet traced and confirmed its function.

2. Power Steering Module
Since I'm not running mazda power steering i'm guessing it can safely go. However, can someone explain to me why this needed a brain? Power steering is a simple hydraulic system, what was mazda doing?

3. ABS Module
I need someone to confirm I identified this correctly. Passenger floor, next to the ECU. Box with almost no markings. Zinc plated goldish color. When I punch in the stamped number on the top I get ebay listings for ABS modules. However. The wires on this connector do not match the mazda diagrams, and this car did not have ABS to my knowledge. So, what would this be, and can I pull it?

4. CPU
This simply does all the relay control for things like flashers, blinkers, etc correct? Meaning since i'm pulling lighting wires, this can come out as well.

5. Check Connectors
There are a couple green connectors on the front harness. (not the yellow fuel pump check connector). These should just be diagnostic connectors for other functions of the car correct?



Yay wires.

Old 12-11-15 | 09:16 AM
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From: tulsa,ok.
At the starter cut relay there is a thin light Green/Yellow wire coming from the alarm unit. The alarm feeds a ground to that wire so as to excite the coil relay and allows the car to start. Thus you would want to ground this wire to bypass its function or you could just jumper the thicker of the two Black/Green wires to the Black/White wire and bypass the relay altogether.
Old 12-11-15 | 09:21 AM
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Yes, you can delete all the power steering stuff.
Mazda used either a speed or RPM sensitive steering control (depending on model)...that's what the little computer box is for.

The CPU controls all the street stuff and since you don't have any, you don't need it.

Of all the check connectors, the only one I've ever used is the "initial set", so I'd keep that.
From the schematic you'll see that all you're doing with it is grounding a pin on the ECU, so you can move it anywhere you'd like. I intercepted the harness at the ECU and ran the wire to a switch under the dash, which just connects to ground.

I want to delete the security system too, but haven't looked into it yet.
It would be sweet if it could just be unplugged but I suspect there's more to it than that, so I'll be interested how it goes for you.
Old 12-11-15 | 09:28 AM
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From: NH
Thanks for the fast replies.

Here's the pin-out on the theft deterrent module as I've pulled from the 1988 manual. Like I said, looks like most of it is just linked to various things that would trigger an alarm. Thanks Satch for the clarification on the start cut relay.

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