Motojunky

Hi all,

I'm a new Cherokee owner, having just picked up a 1999 Cherokee Sport. I had it inspected in MD today and one of the failure items was the brake warning light not coming on. It doesn't self-test at startup or light when the parking brake lever is pulled.

My first thought was a blown bulb. I pulled the dash apart (pleasantly surprised at how easy it was) and found that the bulb was in fact blown. I swapped with the lift gate bulb (tested good) and no joy. I then swapped with the key (sentry?) bulb since I remembered seeing that it was lit. The key light continued to work and still no joy for the brake warning light. I hurried up and put it all back together as it was getting dark and I didn't feel like working with a flashlight.

In hindsight, I don't recall seeing the ABS lamp light. I did not check that bulb.

I'm seeking suggestions as to where to start troubleshooting. I would assume a sensor failure would cause a steady on condition vs. off. I guess "the computer" manages the self-test light cycle. What sensors does it receive input from to do its thing?

I searched forums but all posts were about lights that wouldn't go out.

Thanks in advance!

BlueRidgeMark

Welcome to the forum!

Interesting problem.... I'd check two things for starters:

1. Do you get voltage to the socket when you should?
2. Do you have good ground continuity at the socket?

CCKen

The brake warning indicator lamp is hard wired to the instrument cluster and does not activate when doing the instrument cluster actuator test.


The bulb is powered by the instrument cluster and is looking for a ground to illuminate. The parking brake switch and the brake warning pressure switch on the brake master cylinder proportioning valve provide the ground. The two switches are wired in parallel so either switch will provide the ground to turn the light on.


More that likely the parking brake switch is defective. You can check for continuity in the circuit by removing the instrument cluster, and using an ohmmeter, probe pin cavity 2 at cluster connector C1 (connector on driver's side) with the meter + probe and the meter - probe to chassis ground.


Set the parking brake, you should see continuity on your Ohmmeter. If not, the switch may be defective or its wiring is defective.


Unfortunately if the switch is bad you have to remove the center floor console to get at the switch.


Cluster C1 pin out:



.
Parking Brake switch:



.

Motojunky

Thank you for the welcome!

I did not yet test voltage to the socket. That may be tricky - not sure if I can free up the wiring enough to have the cluster plugged in and still have the rear accessible. Hopefully I can.

I used my meter to test continuity from the cluster plug on that side to the brake light warning bulb socket. I did get continuity, but I got it from more than one pin which I thought odd. Ground side maybe?

It may not be until Friday that I have time to test further, but I'll be more methodical in my approach then. Last night was just a quick check in hopes that it'd be an easy solution (bulb).

Does anyone know how the circuit from the parking brake lever works? Is it a continuity check that the ECU reads and then sends a voltage signal to the cluster based on condition, or is it powered and the switch simply grounds the circuit and lights the light?

I think a service manual would be my friend for this one. The OEM one is fairly expensive - are there viable aftermarket manuals? I haven't really fiddled with cars/trucks for fun in ~20 years so I have some catching up to do.

Thanks!

Motojunky

Fantastic reply, thanks!

Could I just ground the wire that plugs into the parking brake lever switch as a quick test? That wire is easily accessible through the center console.

CCKen

[QUOTE=Motojunky;3308125]Fantastic reply, thanks!

Could I just ground the wire that plugs into the parking brake lever switch as a quick test? That wire is easily accessible through the center console.[/QUOTE]


Go for it. But keep in mind that the wire from the connector to the instrument cluster may be intact but the switch may be defective. By jumping a ground to the connector does not check the switch.

Motojunky

[QUOTE=CCKen;3308133]Understood. I can squeeze in 5 minutes to ground that wire and hopefully "light the light" tonight. It'll be Friday before I have time to pull the dash again.

Thanks again.

CCKen

FYI: Parking Brake Switch Mopar part number is 52127960.


Rockauto listing.


http://www.rockauto.com/en/moreinfo....113074&jsn=234

Motojunky

Tonight's quick troubleshooting results:

Grounding the wire to the switch does not light the light.

The switch checks out good. Both ends are exposed and accessible via meter and it changes state (open/closed) when the brake handle is moved.

My next step will be to check the circuit via C1/pin 2 cavity per your suggestion. If I'm thinking this through correctly, a lack of continuity points to a wiring issue. Continuity would suggest an issue with the instrument cluster.


I may be able to make time tomorrow evening.

Motojunky

This was the clue I needed.

I headed out to the jeep this evening prepared to dig in and get this thing figured out. I decided to ground the plug at the proportioning valve first, just to see what it might tell me. I opened the hood and found it unplugged. I plugged it in and the light works as it should.

If not for that clue, I probably would not have found it until I got a service manual and studied the wiring diagrams.

Thanks again!

Next up is the non working parking brake. The cables all look good and move as they should. Removing the drums should reveal the problem.

CCKen

Can you explain how this worked? Was the parking brake set?


This doesn't make sense to me. The two switches are wired in parallel. The light will come on when the key is turned to start if there a failure exists between the front and rear brakes and the park brake is not engaged.


The park brake switch will turn the light on when the park brake handle is engaged and the key is to ON/RUN and there is no failure detected by the proportioning valve.


See diagrams.



.

Motojunky

I'm replying from my phone and can't quite digest the wiring diagrams. In a nutshell:

The warning light on the dash did not light when applying the parking brake. I did some not very methodical troubleshooting as noted above. I discovered that the plug at the proportioning valve was unplugged. Upon plugging it in, the warning light works as it should. It comes on briefly at startup and turns on when the parking brake is applied (and off when the brake is released).

Is it possible that in later years the wiring changed? Either way, I'm getting expected behavior and appreciate the help!

CCKen

Doesn't get any better than that.