brake switch query - tying into GT500 ABS

[toadster]

trying to button up my driver side footbox before riveting in place, I need to tie in a switch to talk to my ABS HCU
I've heard of a switch being needed, but no pinout was called out in the johngeorge wiring build curious if needed to be honest

I rewired the ABS connector moving Pin10 to Pin6, removing pins 20, 24, 34, 39 from the OEM setup
I do have the CAN+/- tied into the Coyote harness already and all power/grounds setup and wheel sensors

2009_Mustang_C135 (1).png


my question is if there needs to be a pedal switch - can I use the existing FFR switch?

the FFR RF Brake Switch has two sets of pins, the "brake switch" pins are closest to the pedal, and is normally closed - and when you push on the pedal the switch opens and turns on the brake lights

brake switch.png

I believe the clutch switch portion is normally open, and when the pedal is pushed - it connects the signal (is this a correct assumption?)
here's what I need for the GT500 ABS config, see yellow highlight below

Screenshot 2022-12-18 172721.png

would I be able to wire into the same switch? keeping the forward pair for the brake lights, and the rear pair for the ABS connection?
or do I need a separate switch altogether?

[Alan_C]

I am very interested to see how this works out for you. So you are planning to use an earlier model GT500 ABS unit with the Coyote Controls Pack PCM.
Regarding the brake pedal switch, since it is just a on/off switch, I see no reason why you would need multiple switches unless the brake pedal switch is carrying the full current for the brake lights. You could address that with a relay if the load it too high.
I used a 2004 Mustang ABS unit in my MK4, but I also used the Ford PCM for the 4.6L DOHC engine used in the car. I thought the GT500 of that era used the same ABS unit.
Do you know what kind of communication is sent via the Can Bus regarding the ABS? Is it needed and if so, will the Coyote PCM speak the same language needed by the ABS unit.
An intriguing science experiment you have going.

[toadster]

yes, it's a science project for sure

I have my #10 wire moved to #6 location, according to johngeorge's setup this is what worked for him.
in the above diagrams, we wired #6 on the ABS module to a HaaT line - which may not be correct given the GT500 wiring diagram at the bottom which talks to the switch

trying to understand the power circuit with relay at the top of the GT500 wiring diagram
if 86/87 are HaaT, and 30 is the switch to turn on 87 which will transfer power from the 85 (PCM) /86 connection?

https://www.delcity.net/documents/au...ay_diagram.jsp

[jab351w]

my question is if there needs to be a pedal switch - can I use the existing FFR switch?

the FFR RF Brake Switch has two sets of pins, the "brake switch" pins are closest to the pedal, and is normally closed - and when you push on the pedal the switch opens and turns on the brake lights

It's the other way around: for the brake lights the switch is normally-open and closes when the brake pedal is depressed. Based upon the highlighted portion of the schematic, the ABS module wants the opposite to happen: the switch should be closed when the brakes aren't depressed (12V to module) and open when they are (open circuit to module). If your brake switch has both normally-open and normally-closed contacts, you can connect the NC contacts to the ABS module and the NO contacts to the brake lights, with +12V feeding both. Assuming the 12V source feeding the switch is hot all the time this means that the ABS module will see 12V all of the time when the pedal isn't depressed, even when the key is off. This differs from the OEM application shown in the schematic where the 12V feed is switched by the PCM power relay. This may or may not cause the ABS module to remain active all of the time and increase its standby draw on the battery. If it does you could add a relay that's activated in start/run to replicate the function of the PCM power relay and feed the NC brake light switch via that.

I believe the clutch switch portion is normally open, and when the pedal is pushed - it connects the signal (is this a correct assumption?)
here's what I need for the GT500 ABS config, see yellow highlight below

You can verify operation of both sets of contacts with an ohm meter or test light. If you have continuity through the contacts when the switch isn't activated and no continuity when it is, then the contacts are normally-closed, if the opposite then they're normally-open.

trying to understand the power circuit with relay at the top of the GT500 wiring diagram
if 86/87 are HaaT, and 30 is the switch to turn on 87 which will transfer power from the 85 (PCM) /86 connection?

Yes, 86/87 on the relay are hot all the time. The PCM grounds the relay coil (85) to close the contacts and connect 87 to 30, feeding +12V to the brake switch.

[Hoooper]

Not sure what the orientation is for which is NC and NO, and I would verify on the actual switch anyway, but yes you can use that switch to hook up one set of NO connections and another set of NC. Weird but convenient that the GT500 ABS module wants to see the brake pedal on an NC signal rather than just get the signal from the typical NO brake light wire.

[Hoooper]

trying to understand the power circuit with relay at the top of the GT500 wiring diagram
if 86/87 are HaaT, and 30 is the switch to turn on 87 which will transfer power from the 85 (PCM) /86 connection?

85/86 are just the contacts on the coil to move the relay gate. 86/87 are HaaT, 30 is just the high amp output side of the relay, heading to the ABS module and only signaling if the brake is pressed or not. I think this is a simplified diagram and there are actually more circuits coming off that relay in reality. This shows as a relay for the signal wire to signal the ABS module that braking is happening, in reality there likely wouldnt be a relay just for that one signal so likely there are several other circuits coming off that relay in an actual GT500. The ABS module itself it looks like is on at all times per the BEC and SJB at the top of the module. It looks like the ABS computer is turned on by that 10A circuit to 32 (hot on start/run), and the main power for the motors comes in through the 40A and 30A circuits on 31 and 2 (HaaT).

[toadster]

It's the other way around: for the brake lights the switch is normally-open and closes when the brake pedal is depressed.

Based upon the highlighted portion of the schematic, the ABS module wants the opposite to happen: the switch should be closed when the brakes aren't depressed (12V to module) and open when they are (open circuit to module).

If your brake switch has both normally-open and normally-closed contacts, you can connect the NC contacts to the ABS module and the NO contacts to the brake lights, with +12V feeding both.

Assuming the 12V source feeding the switch is hot all the time this means that the ABS module will see 12V all of the time when the pedal isn't depressed, even when the key is off.
This differs from the OEM application shown in the schematic where the 12V feed is switched by the PCM power relay.

This may or may not cause the ABS module to remain active all of the time and increase its standby draw on the battery. If it does you could add a relay that's activated in start/run to replicate the function of the PCM power relay and feed the NC brake light switch via that.

thanks - I tested continuity with my other brake/clutch switch since it's extra (Coyote includes it's own clutch switch)

• the two prongs closes to the button are NC
• the two prongs at the end of the switch (furthest from the button) are NO

it seems I could wire both the brake lights and the ABS sensor to the NO prongs then, no need for a 2nd switch
BUT in the FFR setup the button is always pushed at rest, so I probably can wire to the NO ports on the end of the switch - does that make sense?

I guess my next determination is to figure out if I should put in a relay to the ABS unit and use the brake switch as that trigger for the relay?

[Hoooper]

Well, I suppose it doesnt matter what terminals you wire the brake lights through since they are just going to a relay and you can always switch the high amp side wires on the relay so they match what the lights should be doing. The ABS module diagram though shows that it is closed when released and open when braking.

[jab351w]

thanks - I tested continuity with my other brake/clutch switch since it's extra (Coyote includes it's own clutch switch)

• the two prongs closes to the button are NC
• the two prongs at the end of the switch (furthest from the button) are NO

it seems I could wire both the brake lights and the ABS sensor to the NO prongs then, no need for a 2nd switch
BUT in the FFR setup the button is always pushed at rest, so I probably can wire to the NO ports on the end of the switch - does that make sense?

I guess my next determination is to figure out if I should put in a relay to the ABS unit and use the brake switch as that trigger for the relay?

So there are two sets of terminals on the brake switch. Put the switch in whatever state it is in when the brake pedal is released (switch plunger pushed in). While in that state, determine which set of contacts has continuity. Pick one of those two contacts and connect it to a +12V source (either hot all the time or switched via your simulated PCM power relay). Connect the other contact to pin 6 of the ABS module. With the switch in the same state, verify that the other set of contacts does not have continuity. Pick one of those contacts and connect it to your +12V brake light feed. Connect the other contact to your brake lights. That should satisfy the ABS controller (at least the brake pedal sense portion) and make the brake lights operate correctly.

[toadster]

So there are two sets of terminals on the brake switch. Put the switch in whatever state it is in when the brake pedal is released (switch plunger pushed in). While in that state, determine which set of contacts has continuity. Pick one of those two contacts and connect it to a +12V source (either hot all the time or switched via your simulated PCM power relay). Connect the other contact to pin 6 of the ABS module. With the switch in the same state, verify that the other set of contacts does not have continuity. Pick one of those contacts and connect it to your +12V brake light feed. Connect the other contact to your brake lights. That should satisfy the ABS controller (at least the brake pedal sense portion) and make the brake lights operate correctly.

perfect - this should work with this single switch!

with brake pedal released, the front prongs are 'off', and the rear prongs are 'on'
and with the brake depressed the front prongs are 'on' and the rear prongs are 'off'

thanks all!! I'm so ready to get the footbox sealed up after this update

[jamminj]

Hello Todd
hope things are well
Great to see you are working on your car
I've been working on my frame it will be a while before i even get to start putting my car together
My monster goes to dyno soon

[toadster]

ok - struggling a bit on this part...

Screenshot 2022-12-27 142943.png

I believe this is to only provide key-on/run power - correct?

here's our thoughts:

1. Start/Run 10A Choke Fuse from the RF fuse panel will power #32 on the ABS Unit
2. Pin #3/18 on the ABS align with the Coyote HS-CAN wiring loom
3. Pin #6 on the ABS will be powered with the Start/Run Wire (yellow) which is part of the coyote harness, part of the HS-CAN wire bundle
4. Pin #2 on the ABS will have a 30A fuse inline to the battery
5. Pin #31 on the ABS will have a 40A fuse inline to the battery

the upper left side of the diagram (circled orange) has a PCM-RC relay - which we found from Ford is Pin #60 on the 2018 Mustang C175B CE302 (YE-BU) wire, which runs from the harness into the PDB, then out to who knows where...
Does the PCM need to provide this power? or can we wire a 15A fuse into a HaaT feed?

also from the diagram - does the PCM AND the ABS need to connect to the brake pedal switch?

[jab351w]

the upper left side of the diagram (circled orange) has a PCM-RC relay - which we found from Ford is Pin #60 on the 2018 Mustang C175B CE302 (YE-BU) wire, which runs from the harness into the PDB, then out to who knows where...
Does the PCM need to provide this power? or can we wire a 15A fuse into a HaaT feed?

I don't have direct experience wiring one of these ABS modules, so use the following at your own risk.

That said, you should be able to provide +12V to your simulated PCM power relay from any fused hot all the time source. But something needs to switch the low side of the relay coil (85 in the diagram) to mimic the functionality of the PCM in the OE application. If the PCM you're using has an output intended for this purpose and you can verify that it's grounded when active you can use that. Otherwise one possibility would be to ground the coil of the relay (85) and switch +12V to the coil high side (86) in ignition run/start, while keeping the switched side (87) fed from a hot all the time source. This would provide power to the brake pedal switch in ignition run/start.

also from the diagram - does the PCM AND the ABS need to connect to the brake pedal switch?

That depends on whether the PCM you're using requires a brake pedal position input, and if so whether it uses the same polarity (+12V when pedal released, open when pedal depressed) as the ABS module.