Dash brake light short

[snowball]

Hi all,

The Brake light on my dash is on. It's as bright as when the parking brake is on.

Ive done some basic troubleshooting and I think I have a short.

I say this because I've disconnected the proportioning valve and the parking brake switch and the light is still bright. According to this diagram, there are only 2 things that can activate the light and they're both disconnected.



So is there anything else I can disconnect to see what is causing the tan&White light to stay on? I'm guessing the wire rubbed somethign and is grounded.

Also, on the diagram there is a CKT33 next to the ECU. Can someone translate that and what the E connector is?

Anybody else run into this? any advice?

This is a R1500 burb 350 1990

Thanks!

[ChevyTech]

It could be an RWAL problem.

Here are some threads on RWAL.
http://67-72chevytrucks.com/vboard/s...d.php?t=302690

http://67-72chevytrucks.com/vboard/s...d.php?t=399153

The ECU in the schematic you posted is the RWAL module.

[snowball]

Thanks CT

I forgot to mention that the RWAL was giving me trouble a few years ago. Random errors so i disconnected it.

Also i was digging around last night and noticed that i have continuety between ground and the power wires for the rear stop lights. Does that point to anything?

[ChevyTech]

You're welcome!

If you take a meter and test for continuity between ground the the wires leading back to the brake light bulbs, you will find continuity because, if everything is in place, currant will flow through the filaments in the brake light bulbs and go to ground.

Is the RWAL module unplugged or removed from the truck?

[snowball]

Yes. it is disconnected.

Ok. Continuity makes sense.

[ChevyTech]

If the RWAL module, park brake switch, and metering and proportioning valve wire connector, are all unplugged, the dash brake light should not be on.

I would remove the instrument panel and see in the metal has come loose on the printed circuit and is coming in contact with another circuit. Sometimes this happens right where the instrument panel plugs onto the connector.

[snowball]

Thanks CT.

I'll start digging. Where is this connector? Can I reach it from under the dash or is it mandatory that I pull the whole thing apart?

[ChevyTech]

To get a good look at the printed circuit you are going to want the instrument panel removed and in your hands.

Remove the bezel then removed the instrument panel so you can inspect it in good light to see if it has come loose. Take a pencil eraser and see if the metal moves right where it plugs onto the connector.

If you don't find a problem then you should start inspecting the harness of the truck. I would do this with everything put back together so I can keep checking if the light is on or off while I move the harness.

[snowball]

Thanks CT.

I really appreciate all your help.

[snowball]

CT,

I'm getting ready to do this over the weekend.

If the metal does move with the eraser, is that a good thing or bad? How do I fix it?

I would hate to have the dash all over the place and not be able to complete so if you have any further advice I would appreciate it...

[ChevyTech]

If the dealer had the part in stock I replaced some of the printed circuits.

On some I have come across I used packing tape on to keep them from shorting out (At the owners choice) (an option I suggested). If it is loose right next to where the connector plugs on it, I would tape it as close to the contact area as possible and then carefully plug it together.

On a few I have soldered in wire in place of areas of the printed circuit.

This was a problem I saw on several of the early 1980s cars as they got older.

On your truck make sure the RWAL is not causing this. You said it is disconnected. Does that mean the module has been removed? What do you mean by disconnected?

I would unplug all 3 items, that can turn the light on, at the same time, to see if the light goes off.

Does the truck have wiring splices – not factory – aftermarket equipment, trailer brake unit, or other suspicious wiring messes?

If I had the instrument panel out, and found no problem, I would take an ohm meter and test for connection between the instrument panel terminal that turns the light on and ground. If it is grounded and I can't find the cause, I would unplug the bulkhead connector and see if the meter reading changes. On a vehicle that old, it may be a challenge to get the bulkhead apart.

PS: Are you ggenovez from Chevytalk?

Do you have a link to the site where you found the schematic?

[snowball]

I am.

RWAL was disconnected by means of removing the wires from the RWAL ECU. The RWAL unit is in place but nothing is connected to it.

All 3 items are disconnected. Light is still on.

There are splices in the wiring. The PO added an aftermarket cruise control unit so there are splices in the Stop light switch. Should be isolated...

Can you elaborate on
"connection between the instrument panel terminal that turns the light on and ground."

Also is there a dash ground or is it just attached to the frame?

Here is the place I found the diagram originally.
http://www.truckforum.org/forums/che...vy-only-2.html

[ChevyTech]

On a GMT 400 body the instrument panel ground is right by the ALDL connector but I can't remember off the top of my head where it is located on your square body truck.

Can you elaborate on
"connection between the instrument panel terminal that turns the light on and ground."

According to the schematic you posted in this thread there is power to the bulb for the dash brake light, and the various items supply a path to ground the other side of the bulb to make it light. I would connect the meter between the wire that goes to the instrument panel (the path to ground) and put the other meter lead on ground. If the is a connection with the instrument panel remove the problem is not in the instrument panel.

I went and looked at the schematics using the link you posted. There are some nice schematics there but the description of what vehicle they are for is WAY to wide. When is see errors I don't know what to trust or what else is labeled wrong. There are vehicles included in what the labels state that the schematics are NOT for.

[snowball]

Stupid question.

Does the silver pin #18 go up or down when you plug it in?

Also is there a ground connection on the instrument panel? I'm assuming it's that taught wire that I haven't figured how to get out yet right?

I don't see any frayed wires and when I tried to do a continuety test from pin 15 to ground I did not get any ring.

[snowball]

Never mind. I figured it out by looking at the wear marks.

Here is what I tested so far.

Connect pin 15 (brake light) and 2 ground - No continuity

Took the circuit board off and connected pin 15 to everything for continuety. Pin 17 rang - Gauge fuse.

Pin 2 did not ring.

What am I missing?

[ChevyTech]

Originally Posted by snowball

Stupid question.

Does the silver pin #18 go up or down when you plug it in?

I don't know what you are asking me.
If you mean terminal 18, the schematic only shows 17 cavities.

Originally Posted by snowball

Also is there a ground connection on the instrument panel? I'm assuming it's that taught wire that I haven't figured how to get out yet right?

Terminal #2 in the instrument panel connector in the schematic is the ground.

NOTE: The dash indicator brake light does not connect in any way to the ground circuit in the instrument panel. The ground for the light is at the park brake switch, combination valve, or RWAL module. Read my RWAL threads about the different brightness levels, depending on which item is turning the light on.

Originally Posted by snowball

I don't see any frayed wires and when I tried to do a continuety test from pin 15 to ground I did not get any ring.

That would indicate that there is not a problem outside the instrument panel.

[ChevyTech]

Originally Posted by snowball

Never mind. I figured it out by looking at the wear marks.

Here is what I tested so far.

Connect pin 15 (brake light) and 2 ground - No continuity

Took the circuit board off and connected pin 15 to everything for continuety. Pin 17 rang - Gauge fuse.

Pin 2 did not ring.

What am I missing?

Pin two should be connected to ground.

The schematic could be the wrong one because the other information at the post was not concise.

Do the dash lights work right, as well as the other gauges?

[snowball]

Sorry for my last posts. Long and tiring day.

Everything else works fine on the instrument panel.

Did confirm that pin 2 connects with ground.

I think it's a wiring problem in the harness and here is why.

When I touched pin 15 to pin 2 it didn't ring BUT the meter counted down to about 520.

When I touched pin 15 to the e-brake wire which should have rang, it didn't but read 520 as well.

When I touched pin 15 to the frame it also didn't ring but read 520.

All this with the instrument panel sitting in my dining room

So, I started with the wire by the master cylinder and it goes under the the master cylinder and over the engine. and I lost it.

So does anybody know the path of that wire? It connects to the e-brake so is there a connector or is it soldered to the e-brake wire?

Any ideas would be greatly appreciated.

[snowball]

Hey CT,

Do you know where the brake diode is located?

I got the combination switch connector to ring when I touched ground, but it doesn't happen when I touch the ebrake connector.

According to page 120 there is a C118 connector and page 121 there is a diode connection C290.

http://www.73-87chevytrucks.com/tech..._Manual%20.pdf

Any idea where those are located?

[ChevyTech]

I don't know where the diode is located.

If the combination switch (Center terminal) had connection to ground, then it is turning the light on – If it is truly a low resistance connection to ground.

The park brake switch terminal will not be connected to ground IF the park brake is not applied.

That PDF in over 16 megabits. That is to much for what I am accessing the site with today. Today is a busy day for me.

[snowball]

NP CT.

Thanks for all your help as always...

[snowball]

Found the issue. The wire from the master goes over the engine and followes the ECM wires. The conduit over the engine failed and the wire was rubbing on the block.

[ChevyTech]

Thank you for letting us know what you found.

That type of failure is very hard for most people to track down.
Good Job!

[snowball]

I'm very tenacious. And obnoxious with my questions and posts.

Thanks for your help. I hope you enjoyed the 16MB of diagrams....