Need some help, Electrical Issues.

[drew23]

I have a 99 Cherokee Sport. 4.0, 4WD, Auto, Non-ABS. I have had the "no bus" pop up and the gauges go dead once before. After shuting it off and restarting it was fine. I now have developed a beep under the dash when I press the brake pedal. It only beeps when the key is off and the pedal is pressed. My brake lights are also coming on when the key is on. They brighten up a little when the pedal is pushed but they have been hot enough to distort my taillight lenses on the top.

I have checked the brake light switch with a meter and reset the plunger and the problem continues. Any ideas?

Rundown as follows.

1. Beep when ignition is off but bake is pressed
2. Brake lights on when key is on.
3. NO BUS status- Contacts need cleaned right?

Any help would be appreciated.

[bluedragon436]

I'd say pull the positive off the battery and touch it to the negative for about 30 seconds, as this should reset the ECU... (never hurts to get a clean computer).. and while that is chillin unhooked, pull your gauges and clean those contacts up and put it back together... got to AZ or your choice of parts store and pick up a new $15 brake switch (never hurts, at least you'll know it's good).. put it in and then see what it does once you hook it all back up and try it again... as far as the beep under the dash that is a bit odd, at least as far as the other issues... but then again, it is also making me wonder.... when you have this beep going on with the key off... and the brake pressed, is the headlights cutting on or even the marker lights?? Sounds like a stupid question, but almost wondering if it might not be the headlight switch or something to do with the lights shorting out.. cause if you have the marker lights or headlights on and cut the Jeep off it beeps or buzzes.. so wondering if that is the sound going on....

[drew23]

Time to get to work, that makes sense that a short in the lights may be causing the beep.

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[drcherry]

On the left side above the kick pad is a white connector with a large bolt through the center. Remove the NEGATIVE terminal from the battery. Then remove the bolt from the block. disconnect the block. Using a 'acid brush', clean the contacts with some WD40 and reconnect the block. Then reconnect the battery. The problem is caused by corrosion on the serial data contact in that block. The instrument panel is driven by a serial data connection to the ECU. Cleaning the contacts with WD40 ends the gauge problem.

[NW99XJ]

On the left side above the kick pad is a white connector with a large bolt through the center. Remove the NEGATIVE terminal from the battery. Then remove the bolt from the block. disconnect the block. Using a 'acid brush', clean the contacts with some WD40 and reconnect the block. Then reconnect the battery. The problem is caused by corrosion on the serial data contact in that block. The instrument panel is driven by a serial data connection to the ECU. Cleaning the contacts with WD40 ends the gauge problem.
I'm very curious to see if this will work....

[drew23]

I'm very curious to see if this will work....

Hope to try this as soon as I get off work. I'll let you know.

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[drew23]

Removed the connector and brushed with WD40. Brakelights still come on as soon as the key is on. Still beeping with foot on the pedal. Any more ideas? Still have to do the gauges.

[NW99XJ]

Anychance you could get a video of whats going on?....I'm particularly interested in the "beep" ...more so the tone of it than anything...
I'm wondering if it's a tone being generated by a relay that has the internal microswitch "fluttering" and thats what your hearing, (i've heard this before - in other vehicles)
...or if its the door chime/headlight on & key on/door open warning beep....

Do the turn signals and hazards work as they should?
What happens if you unplug the brake switch?
Have you checked the fuses for the brake light & tail light circuits?
(corrosion on the fuses could cause a voltage drop which may or may not be contributing to the problem)

I'd also be going corner to corner and inspecting each light socket to ensure there is no corrosion, or anything shorting out.

[drew23]

UPDATE on the situation.

I think I found the problem. When I got home last night from a meeting at the fire department I opened the back hatch with the Jeep running. As I opened the hatch the brake lights went off. I shut the Jeep off and pressed the brake pedal, NO BEEP. Upon inspection I have several broken wires in the rear hatch harness. Could a short here be causing the problems? Seems to me the only logical option. I am going to try to get it to beep again and I will video it just for others a future reference.

Drove to work this morning and everything is acting fine.

Still don't understand the beep but, maybe I'll figure it out upon further inspection.

Thanks everyone.

I'll keep the post updated as much as possible.

[NW99XJ]

CORRODED, BROKEN, OR SHORTED WIRES WILL ALWAYS CAUSE ISSUES.
The corrosion will not allow the electrons to flow properly, increasing the resistance on the circuit, and decreasing voltage and amperage.
Broken wires, well, obviously wont allow any voltage to pass, and can lead to shorts....all of this can cause all sorts of havoc in an electrical system.
Patch, fix, or otherwise replace the broken/ corroded sections of wire in the harness, and you should be good to go.

Good luck!