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No Brake Lights or Hazards


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Ok, some of you may have seen my post about no brakes. Well I got that solved and now guess what?

 

NO Brake Lights or Hazards

 

Turn signals work, but do not alternate with the marker lights, as it used to. Headlights function fine and parking lights are ok.

 

Everything functioned perfectly before removing the rear proportioning valve. I also replaced the master cylinder and booster.

 

What could cause this? Could that brake warning connector on the front metering block be at fault somehow?

 

I just don't think the hazard system is getting power, or else grounding issue somehow.

 

Any ideas?

:headpop:

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Ok, I'll check anything about right now. I checked the rear ground behind the tail light and cleaned it. However, I don't think the hazard circuit is getting power. The only thing I monkeyed with was the brakes. Could a relay be at fault? Strange that this just happened after my brake issue.

Keep throwing em out here guys.

:nuts:

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Ok, some of you may have seen my post about no brakes. Well I got that solved and now guess what?

 

NO Brake Lights or Hazards

 

Turn signals work, but do not alternate with the marker lights, as it used to. Headlights function fine and parking lights are ok.

 

Everything functioned perfectly before removing the rear proportioning valve. I also replaced the master cylinder and booster.

 

What could cause this? Could that brake warning connector on the front metering block be at fault somehow?

 

I just don't think the hazard system is getting power, or else grounding issue somehow.

 

Any ideas?

:headpop:

 

Have you checked the fuses to make sure they're all good?

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Gotta be either fuse or ground. Did you disturb any wires back there when messing around with the rear proportioning valve?

 

By the way -- are you certain your side markers alternated with the turn signals? They were't that way from the factory until 1997 in the Cherokee. I don't believe the MJ was ever set up to do that, unless an owner modified the wiring. I KNOW the '88 isn't supposed to work that way.

 

Did you by any chance disturb the switch on the brake peddle when doing the master cylinder? It's a mechanical switch, not run by hydraulic pressure. If it's not set correctly, it won't activate the brake lights when you step on the peddle. I don't think this should affect the hazard warning lights, but be sure to eliminate all possible variables.

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First Off; Thanks I greatly appreciate all the help I have gotten here.

 

 

I double checked all fuses in the cab and they are all good.

I lack a good electrical schematic but am attempting to trace the power input to the Hazard Flasher because I have no power at the Hazard flasher. Which way does the power flow? From the flasher to the brake switch and ,then, to the hazard switch, or the other way around.

I thought the power flowed from the key to the hazard switch and then to the brake switch, and then to who knows where? Ha!

Not too sure I understand this Flashing Brake light operation.

If the flasher grounds, as my schematic seems to show, why then does my Cherokee have power at one of the hazards flashers plugs?

 

That mechanical switch on the brake pedal, should not have been harmed or damaged. I only removed the bolt which connects the pedal to the brake booster arm, and to which it is attached. I replaced the booster and master.

However, I will check this mechanical switch.

 

I don't see any relay that could be involved?

All grounds seem good; I cleaned the rear ground behind the drivers side tail light. All lights are good.

 

I'm sure it's something stupid. Could I have knocked anything lose which feeds the power to the Flasher circuit? Fuseable links?

The flasher and brake circuit are idependent and powered from a hot lead attached to the top of the steering shaft in the cab; Right or wrong?

 

About your question on the signal operation; Yes, i've had this vehicle since new. One owner, me. It's only left my view twice in seventeen years for service I could not do. It has never been monkeyed with in any way. Ah, untill my little brake mod started three weeks ago that is.

 

The turn signals flash then the side markers flash; they alternate but only with the parking lights on or the head and parks on. I thought they always did, but can't be sure since this brake light problem and hazard issue could be causing interference. Being old doesn't help a hell of a lot either, and I don't mean the truck. The 88 Cherokee does not alternate but I have since discovered that the flasher units were put in the wrong spots. The 522 was in the place of the plastic factory unit and vise versa.

Swapping those caused the signals to begin functioning at a normal pace. Before they flashed like they had bad grounds, which the do, but that could also be responsible for a variety of flasher issues. I was amazed to discover how critical the bulb types are to correct functioning. Who knows, maybe the only difference between the 88 and 90 Comanche are the types of bulbs!

 

As soon as I get this idiotic brake and hazard problem solved I would like to look into this more.

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The difference in the flashers is that the stock turn flasher is a load-sensitive type (unless you have a factory tow option). They do that specifically so that the flash rate changes if any bulb burns out. That's supposed to alert you, but most people don't seem to know that so they ignore the fact their turn flasher is blinking twice as fast as it was yesterday (or half as fast, or not at all, depending on the flasher).

 

The hazard flasher is the heavy-duty type, which will always flash at the same rate, regardless of how many bulbs it's pushing. They use the same one on the turns if you have trailer wiring, so the added lights of the trailer don't have the turns flashing at 60,000 hertz. The sockets are the same, so they will interchange.

 

If the flash rate changed considerably when you swapped the blinker modules, that's a clue that there's a problem. The stock turn blinker would NOT be happy with a bad ground, which increases resistance in the circuit and puts more load on the blinker module.

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Gotta be either fuse or ground. Did you disturb any wires back there when messing around with the rear proportioning valve?

 

By the way -- are you certain your side markers alternated with the turn signals? They were't that way from the factory until 1997 in the Cherokee. I don't believe the MJ was ever set up to do that, unless an owner modified the wiring. I KNOW the '88 isn't supposed to work that way.

 

Did you by any chance disturb the switch on the brake peddle when doing the master cylinder? It's a mechanical switch, not run by hydraulic pressure. If it's not set correctly, it won't activate the brake lights when you step on the peddle. I don't think this should affect the hazard warning lights, but be sure to eliminate all possible variables.

 

Only the 91-92 MJs had the alternating turn/side markers. If you have that on your rig, it's been installed by a PO. Easy to do. The emergency flasher circuit is independent from the brake lights and turn signals. The flasher power is connected directly to the battery +, through a fuse, to the column switch, then to it's own flasher, then to the four corners. The only commonality is the bulb socket grounds. The flasher circuit also goes through the alarm/chime module. So if the corner light grounds are okay, try pulling the chime module and see if that might clear it up.

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