Eric in Chicago

I am trying to wire a warning light to let me know when the ABS has tripped. I have a ABS reset switch wired to relay in the fuse box and was wondering if there was a way to wire a light to come on when the relay was tripped? does anyone has a gauge panel elet. schematic and could help me identify the wire that I would need to tap into to run a LED light? I would prefer to use a standard warning light like the Longarce model but being an electrical idiot, I do not know how I could set up a circuit without using the low voltage dash light power feed. Thanks in advance for any help!!

Eric in Chicago

Bump for the evening viewers.

centerpunch

What exactly are you doing, and what do you want the light to show?

When you say "the ABS has tripped," what do you mean?

Eric in Chicago

During a race, I have tripped the ABS into the off mode. ABS will fail into the off mode after hitting a rumble strip, or at track out hitting the dirt and or pot hole at the edge of track out. While it the heat of battle I am unable to see if the ABS light goes off. I have a ABS switch wired to the relay in the fuse box to reset the relay but when holding off a couple cars behind me or in a battle with a car in front of me, it is easy to forget to look down to see in the tiny ABS warning light is on. I lost 2nd place in a race last season when I did not notice the ABS was tripped, went into a hot brake zone and flat spotted my tires. When the tires flat spotted I lost 1/3 of my braking as the tires would slid instead of stopping. This allow the guy that was on my tail to get by me with 3 laps to go. I would like to mound a light (LED if I have to tap into the dash light as it is low voltage) or if someone has another idea to trigger a normal 12v light off the relay when the switch goes into failure (off) mode. A flat spotted set of tires are worthless and at 1200.00 a pretty expensive mistake that could be cured with a warning light.

Bri Bro

I need a question answered. How does the ABS reset operation under normal conditions? From the wiring diagram, there is a main ABS relay that supplies power to the ABS control unit and the Hydraulic unit. I am guessing that your reset switch is cycling power to the relay which cycles power to the ABS. There is a wire (white) coming out of the ABS control unit that goes directly to the ABS light in the dash. It can be tap into on a four pin plug (t40) pin 4. Is this a 5V signal?

Driving a 12 volt light from a low voltage signal just take a transistor and a couple of resistors. You pick out the light you want, send it to me and I will add in the driver circuit. Are you looking for this type of light?
http://www.pegasusautoracing.com/pro...asp?RecId=1855

BTW: Is this your 91 944 S2?

centerpunch

I have never heard of ABS turning itself off. Maybe you just have a bad relay or intermittent connection to begin with.

hderr

Perhaps I don't understand what you would like to do, but if you would like to be alerted to an event without having to look down at a light, I wonder if a buzzer wouldn't work?

Bri Bro

I was reading the manual trying to gain a little knownledge on the subject. It states that if the difference in rolling radius (wheel speed) exceeds a certain amount on the wheels, the control unit will deactivate and the ABS pilot light will come on. It states that the different wheel speed are interpreated as different road speed at the cars axles. One way the manual states that this can happen is by using unapprovied tire dimensions. I am sure racing can have the same effect on generating a difference in wheel speeds on the axles.

Oddjob

Pretty common occurance for track cars with stiff suspension and stiff tires. More vibration and bump impact is transferred through the suspension, which is picked up by the ABS sensors. The ABS ECU is detecting an irregular signal, and it thinks there is a fault in the system, so it shuts itself off - but its not an actual power down, nor is the relay tripping. There is still power to the ABS circuit (which goes to the ECU and the Hydraulic pump). The brain just does not operate the ABS pulse function (if there is something wrong with the system, the ECU may pulse when unnecessary and not allow the car to properly apply the brakes when needed - so for the fail safe mode, the factory programmed the ECU to shut down the system if it thinks there is a problem somewhere).

When the system faults out, the dash "!" and "ABS" warning lights will stay on, and the ABS will not function - so you have a basic standard non-ABS braking system.

In order to get the ABS ECU to start working, it needs to be reset (or powered off). Since you dont want to have to shut off the car while driving on the track, its common for racers to put in an ABS reset switch (cutting power to the relay, or cutting power to both the ECU and Pump). Porsche realized this problem and solution back in '87, and so the factory Cups have an ABS reset switch on the center console for this reason.

If you want to add an additional warning light or buzzer, Im thinking you need to splice into the wire going from the ABS ECU to the instrument cluster. I think this is a white wire off pin #29 on the ABS ECU (confirm with a wiring diagram if you have access to one) There is a plug connector (4 wires) that connects the ABS wiring harness to the main wiring harness - the connector is under the glove compartment. It may be easiest to tap into the wire there. But Im not sure if this signal wire will be able to light up a nice big/bright warning light, or if you will need a separate power wire (I avoid electrical engineering like the plague...see Brians notes above, looks like he is into that kind of ****.).

Eric in Chicago

Thanks Brian!
Yes, it is for my 91 S2. I dont have the factory wire diagram so I dont know the volt/amps but I am sure is is low power. The link to the light is the one that I was looking to buy. As Oddjob states below, the reset switch shuts the abs off and when the switch is flicked back on the system is reset. If someone wanted to get really fancy they could hook up a micro switch to reset the relay when the light came on. A warning light would do just fine for me. I would be happy to send you the light if you know how to hook up the right resistors/transistor to make it work. I would be happy to pay you for this service and if your interested in setting up a kit, I am sure more than a few racers would happily pay you for that service! PM me with your address and I will order the light.
Still need to confirm the wire on the inst. panel to tap.

Oddjob,
I am not sure if tapping into the ABS ecu wouild work as the relay is what is being shut down not the ECU, but I could be wrong...

As for a buzzer straight pipe on a race engine, helmet on, radio ear plugs with spotter telling me how slow I am, cup cars flying by me at 110 db's and wind noise... Not a chance of hearing a buzzer!

Thanks for the answers, is this a great place or what?!!!

Bri Bro

I would be happy to do this, it is really a simple circuit and the current to drive the device will not be an issue. Just have to use a high gain darlington transistor. It will require that you have the signal, 12V power and gound to make it all work. Just drop me a PM when you get the light you want and I can put it together in a flash.

On a side note, you could auto reset but that could cause real issues if the ABS truely is not working correctly. I am not sure it is worth the risk but it wouldn't be hard to do.

Kyle Donley

ABS is for street cars.

Oddjob

Your reset switch will cut power to the relay (the common way of installing the switch), which in turn cuts power to the ECU and Pump. But the ABS Fault Detection/shut down is internal to the ECU and has nothing to do with cutting power (tripping) to the relay.

Another thought on this - its probable that the ABS warning light on the dash is a grounded light (my terminology may be incorrect), meaning that for the light to be shutoff, the instrument cluster needs a 5V signal from the ECU. If the ECU faults out, it will stop the 5V signal, the same as if the ECU loses power, and the light comes on.

You will need to check that white wire from the ECU to the instrument cluster with a multimeter, and see if there is voltage/current when the system is functioning, faulted out and/or switched off.

centerpunch

When I bought my Turbo Cup car from PMNA in 1987, I was told the switch (which turns the ABS off when you push it in, and back on when you pull it out) was because many race drivers do not like ABS in the dry, but virtually all like it in the wet.

In 19,000 miles, many of them on the track, I have not once had the ABS turn itself off or the ABS or exclamation point light go on by themselves. (I have had the ABS act goofy when I get two wheels off, but it always works again at the next turn.)

centerpunch

But assuming this problem does shut down a function in the ECU, perhaps powering the ABS off and back on triggers the ECU to reexamine the ABS, and then seeing it appears to now be OK, re-engage it.