Brake light on. Codes?

[ASEASIDER]

Chevy Tech,
I installed the switch on my '90 K-5 Blazer 350 700r trans as you instructed me to during lunch today, the light came back on. But while I was under the dash I notice another switch that is actuated by the brake pedal, (if you are looking foward) it's to the right of the brake light switch up a little higher with a red/ black wire and a purple wire comming out of the switch. On the purple wire someone attached a jumper that fed down to the switch on the driverside transmission (a 700R). Do you know what they were thinking if they were thinking? Do you think Auto Zone has a scanner that can read my brake light issue? My scanner is not able to read the fault. Any suggestions? I unplugged the 6 pin connector so I wouldn't have to look at that light for the time being.
Thank you

[ASEASIDER]

Oh I jumped pins A-H and still same code 10

[ChevyTech]

I don’t think Autozone will have scanner that can read this. You got the code already. We will figure out the reason it sets a code 10.

Your trucks is a square body R/V body style which has a different brake switch configuration then the newer C/K trucks. I am going to go back and edit my earlier reply to you so this thread is cleaner for other people to use.

I don’t have a schematic in front of me for you truck but I think the purple wire they spliced into is for the RWAL system.

You are going to have to figure out what the spliced wire is for. You will most likely have to remove the spliced on wire, from the RWAL wire, and figure out where it should have been connected.

Some of the wire colors should be the same as the newer C/K trucks.
1993 schematic brake switch wire colors:
Brown - power from “BRAKE” fuse to switch – circuit 439
Pink//black - power from “ECM/IGN” fuse - circuit 250
Purple – To antilock module – circuit 420
Orange – power from “STOP-HAZ” fuse – Circuit 140
White – brake light out to turn signal switch – circuit 17



I am not sure this will match your Square body truck but if I remember correctly it will because I think the module is interchangeable.
Module 6 wire connector
Terminal “A” – Ground.
Terminal “B” – power with key on. Fused
Terminal “C” – Power key off or on. Fused
Terminal “D” – DRAC speed output signal & ALDL terminal “H”
Terminal “E” – brake warning lamp, park brake switch circuit, and combination valve switch.
Terminal “F” – power signal from brake pedal switch and 4 wheel drive front axle switch

Take a meter to the six wire connector you unplugged and check for voltage on terminal F.

Terminal F should be within ONE volt of battery voltage with the key on and brake pedal not pushed.

[ASEASIDER]

Chevy Tech,
Will try your suggestions, any idea what the switch (or wires) comming out of the driverside tranny 700r that the other owner spliced into is? Or what the other switch next to the brake light switch is? Just trying to figure what the previouse owners logic was.
On my '90 K5 350 700r trans. I cut the jumper and no difference in the peformance of the Blazer shifting etc.. during a 60 mile run home after work on Fri (this afternoon). I got on her a couple of times because of Friday afternoon (knuckle head) traffic. Other than that one splice all the wires under the dash look good. I would like to have a heart to heart with the guy that invented the little blue splice connectors. You should have some sort of liscense to purchase them. Thank you!

[ChevyTech]

The wires going into the side of the transmission are for the lock up torque converter.

Switches at the brake pedal are for the Brake lights, RWAL, Cruise control and lock up torque converter.

The torque converter needs a power feed through a brake pedal switch just like the RWAL does. The Torque converter circuit could have failed so someone piggybacked onto the RWAL feed instead of fixing the problem. Now the problem has damaged a second set of contacts or wires, taking down the circuit that they spliced into. You need to separate the circuits like they were built to be, and fix the damaged parts.

My guess is the lock up torque converter on your truck no longer works.

Later today I will try to find time to see if I can find some good schematics that will help you.

I will not use the blue scotch locks!

[ASEASIDER]

I understand know their thinking, I didn't know what the switch on the side of the trans was. Anyway to check that system out. No way I plan on getting this system back the way it rolled off the factory floor :. I just need some steering in the right direction.
Thank you

[ChevyTech]

I looked a bit and did not find schematics that were good.

You can go to AutoZone’s site and register so you can view schematics there.

If you do the tests in my post four above this one, and see if power gets to terminal F of the six wire connector to the RWAL module, that will tell us if the brake switch/ circuit is the problem.

If you find no voltage a terminal F you just need to work your way back through the circuit with a test light until you find the problem.

[ASEASIDER]

Chevy Tech,
I did a voltage test on pin F (purple wire) and no volts. While I was there I didn't have any volts on any of the pins. I followed the pin F (purple wire) down near the firewall where it comes to a connector and the purple turns into a Purple /white. The purple/white wire runs inside the cab near the fuse box and ties into a plug that has some type of resistor (looks factory installed). I unplugged the resistor and tested that it had 4.47ohms. Plugged it back in. And tried to follow the purple/white and white wires up into the dash, but ran out of time. Any idea on how I can get power where I need it. Will log on AutoZone web sight and see if I can find some more info.
Thank you

[ChevyTech]

I did a voltage test on pin F (purple wire) and no volts. While I was there I didn't have any volts on any of the pins.

Did you have the key in the on position?
Have you checked the fuses?
You are testing for voltage on the wire harness and not the module, correct?

If there is no power on any terminal there are bigger problems then a switch, but I am concerned you are not testing correctly, or are unsure of using a meter.

[ASEASIDER]

Chevy Tech,
I tested the wire harness not the module with the key in the on position not the ACC position (fan blower was blowing).
The meter was set to Volts DC and after the first test that resulted in 0 volts, I connected the meter directly to the battery (to verify the meter was good) and had 12.3 volts comming out of the battery. Went back and tried the harness with several different ground spots for the meter and still no volts. Fuses look good pulled and tested them all. VERY familiar with meters, my co-workers as well as my life depends on my ability to use ELECTRICAL meters for wireing up ORDNANCE 1.1 (the big stuff thats leaves a hell of a crater if you should screw up) on a daily basis.

[ChevyTech]

If the RWAL module was not getting power you would not have been able to retrieve trouble codes from it.

Terminal “A” is a ground.
If you test for voltage on terminal ”C” using terminal “A” as a ground for the meter, there should always be voltage at terminal “C”.

Be very careful what you use as a ground for your meter.

Your vehicle could also have body ground wire problems.

[ASEASIDER]

Will try "A" and "C" in the morning, what if I try "A" and "F" well

[ASEASIDER]

I couldn't wait went and check it A to C = 11.73 volts. A to F = 0 volts

[ChevyTech]

You should have had the key in the on position when testing for voltage at terminal “F”

“F” is from the brake switch.

Power to goes through a fuse in the fuse box – to the brake light switch – to the RWAL terminal “F”

Find the purple wire at the brake switches. It should have power with the key on. If not, check the wire next to it in the switch which should be the wire bringing power to it from the fuse box.

[ASEASIDER]

Will do in the morning, when I checked "A" to "F" the key was in the ON position.
Thank you again

[ASEASIDER]

Chevy Tech,
I found the Purple wire on the brake switch, the switch that is towards the passenger side, not the brake switch that I replaced that one was towards the left and fixed my cruise control problem. Anyway comming off the switch that had the purple wire it also had I believe a red/black wire comming out of it also. I tested the voltage on the purple wire and then voltage check on the red/black wire they both were within a volt of battery voltage.

[ChevyTech]

If you have power at the brake switch end of the purple wire, and not at the RWAL end of the purple wire, then go test for voltage at the resister you found which is in between the brake switch and the RWAL module.

It sounds like you are getting very close to finding the problem.

You should go to the AutoZone site and get the schematic and attach it to a post here.
You may need to save it to your computer and then down load it to a post to get it to show.

[ASEASIDER]

No voltage at the resister (resistor goes to 1 purple wire and 1 white wire near the fuse box) between the brake switch and the RWAL module. All fuses looked good just went and checked them again.

[ChevyTech]

There is a resister between the RWAL module an the brake switch but I think you may be looking at something else because I am fairly sure the wire is purple all the way from the Brake switch to the RWAL module.

NOTE: you may find a diode that connects this circuit to the factory circuit for the torque converter clutch circuit. Something has to tell the torque converter system when the brake pedal is pushed.

I just can’t take the time to hunt down a schematic for that old truck and I don’t keep anything that old for future use. The amount of information I save is cumbersome just to index it all.

I am going by memory on this. I think you are very close to finding the problem. You need to compare what you are looking at with a schematic for your exact truck.

The RWAL circuits are different between different models in the same model year. Different year trucks are going to have similar circuits for the RWAL but definitely will have differences.

If I were working on it could possibly find my way through the circuits. This is way too old of me to get anymore detailed by memory from something I have not seen for so many years.

Here is a link to One RWAL information site. It is a good site for people with a low brake pedal that are wondering if the RWAL is causing it.
http://www.aa1car.com/library/abs_kelseyhayes_rwal.htm

[ASEASIDER]

I understand and if you are going from memory WOW!!! I tested for continuity between pin #7 on the ABS module harness and the purple/white wire inside the cab and I have continuity. At the engine compartment firewall is where the purple turns into purple/white. Is there anyway I can test the ABS module it self to make certain it pin #7 is doing what it is suppose to be doing.
Thank you very much for getting me this far

[ChevyTech]

By pin #7 I think you mean Terminal “F”

If there is continuity, then voltage should make it through the wire unless there is a poor connection so as any load is put on the wire no currant flows.

Double check for voltage at both ends of the purple wire. I may be that the brake switch works sometimes and doe not work other times, and is messing with your test results.

Also if you are moving wiring next to the problem it could be making and breaking connection.

I like using a test light because it puts a little load on the circuit.

Be suspicious of any connector the wire goes through.

We test modules by installing known good module.

You are lucky you have an early RWAL module because the later modules would not be capable of blinking out the code 10. It could only be read with a scan tool.

[ASEASIDER]

I am sorry, thats right I was referring terminal F to pin 7. My bad, I was working on other stuff along with this nighmare. I did dig my test light out this morning and started to check for voltage and then measured it with my meter. I made a run to the parts yard today and purchased 3 of these ABS Modules to very that the two I already have are good. Well the ones from my local yard function just as the two I already have. I am out only $10.00 (for the three used ABS Modules) on that test.
Maybe a few days before I can get back to testing, bad weather is comming thru and my garage is full two other trucks in there.
Thank you!!!

[ChevyTech]

You should have grabbed a brake light switch, when you were grabbing modules.

There is an extremely good chance that the brake light switch is the problem, and you are not catching it with your testing.

[ASEASIDER]

Dang!!!!! You are right, I rode out to get gas for my chain saw and was thinking about testing the module. Anyway I looked @ my gas guage and figured I have enough gas to make a trip to the salvage yard about a hour drive each way. Didn't even think about the switch, oh well I can get one from NAPA for around $10.00 or so. Will try later on this week. If you need a module let me know

[ASEASIDER]

I did some more digging tonight. I found that the jumper wire from the transmission TCC is spliced into the purple wire going to the Cruise Control Actuator (the switch next to the brake light switch). I tested the Cruise Control Actuator' out and it seems fine but I am going to replace it anyway(CHEAP PART). My next step is to replace the Cruise Control Actuator, then I am going to disconnect EVERYTHING that has to do with the electric brake setup and drive the dang thing to see if the light comes on again. Unless anyone has some good suggestions.
Thank you