How Do You Test The Idiot Brake Light

[Gregski]

putting together a '71 GMC 1500 350/350 basket case, the truck has the wiring harness for a gauge cluster with gauges, but I am missing the cluster/gauges itself, so I am making my own DIY gauge panel and have the high beam idiot light working as well as the turn signal indicator lights, but I can't get the idiot brake light to work

I did some forum searches and I read that the brown wire connects from the bulkhead to the distribution block (I have drum/drum brakes) which I have connected, and when grounded out it will light up the brake light, I read that it also should light it up when you first go to start the truck, well mine does neither

I tried to test the light with the ignition in the ON position by manually grounding out that brown wire that would plug in to the distribution block but no joy

so my question is how do I get that pesky red light to glow, just to make myself happy, I know that for it to really light up I would have to be pretty SOL with the brake fluid, but I should see it glow upon start up

FYI: the gauge panel aint much to look at as the PO hacked it up pretty good, so I am doing the best I can with it, also I know that this one is the one without gauges, but this is what came with the rig, though it was not installed, just thrown in as extra

thank you

[VetteVet]

The wiring for the brake warning light runs from the distribution block to the key switch and then to the gauge cluster plug. It is shown in the diagrams below.

The 20 T wire on the ignition switch is the BW light wire and it runs from the key switch to the no. 2 terminal on the cluster plug in both the gauge cluster and the idiot light cluster. This is the grounding side of the light and is open to ground until the distribution block switch is moved by uneven brake pressure.
Or whenever the ignition switch is turned to the start position which will ground the brown wire to complete the circuit to light the light. You should be able to ground the 20T wire at the distribution block, and light the light if the key is on.

The temperature light wire (green) parallels the brown wire to light the temperature idiot light whenever the start switch is moved to the start. position.
It is connected to the no.5 terminal on the idiot light cluster plug, and it is eliminated on the gauge cluster plug.The temperature gauge wire is moved to the no.6 terminal for the gauge cluster to complete the circuit for the temperature gauge to ground. The ignition switch may not have the green wires in a truck which has a gauge cluster.

Here is the diagram showing both the cluster plugs and how they are wired.

Don't pay any attention to the black arrows as they are for other circuits.



Now you should know that the power for the gauge cluster is provided by the pink wire which went to the no. 7 terminal on the OE cluster plug and it is moved to the no.3 terminal on the gauge cluster plug. It provides power to the fuel gauge and the temperature gauge on the stock gauge panel.

It appears to me that you do not have the circuit panel and are wiring the gauges and lights manually. Is this the case? Either way here is the wiring for the gauges and lights for the gauge cluster panel.




Notice the wire on no. 3 pin is the pink wire which powers the fuel gauge, the temp gauge, the brake warning light, and the temperature warning light if you still had one.

Be advised that you will have to change the temperature sensor in the block if the truck had the idiot light cluster from the factory.

I see by re-reading your post that you have tried to test the BW light by grounding, but do you have power to it from the no. 3 terminal or the fuel gauge as in the diagram above?

The pink wire originates at the fuse pane and is fused by the clstr pnl fuse. A 3 amp fuse IIRC. With these diagrams you should be able to wire the gauges and lights without the circuit board if you go slow and be careful.

[Gregski]

Wow, thank you so much

Originally Posted by VetteVet

The 20 T wire on the ignition switch is the BW light wire and it runs from the key switch to the no. 2 terminal on the cluster plug in both the gauge cluster and the idiot light cluster. This is the grounding side of the light

Bingo! I thought it was the positive side... Wrong!

Originally Posted by VetteVet

It appears to me that you do not have the circuit panel and are wiring the gauges and lights manually. Is this the case?

That is correct, I am essentially deleting any stock engine management gauges and using my own digital ones. The exception being the idiot lights.

Originally Posted by VetteVet

Notice the wire on no. 3 pin is the pink wire which powers the fuel gauge, the temp gauge, the brake warning light, and the temperature warning light if you still had one.

That's the gold nugget I was looking for, the first diagram which I had only said it was the Fuel Gauge feed.

Originally Posted by VetteVet

I see by re-reading your post that you have tried to test the BW light by grounding, but do you have power to it from the no. 3 terminal or the fuel gauge as in the diagram above?

No sir, that's what I was missing, I had no way of knowing how the power traveresed the circuit board, so your second diagram is very helpful, I have never seen that one before, I have the first one you shared.

Thanks again, I can't wait to try this first thing tomorrow morning.

[CG]

Where do these color diagrams come from? Id like to take some of them and redo in Illustrator (very time consuming) and make garage art that's also useful.

[special-K]

How do you test the idiot brake light? Run the truck like a bat out of he!! up to a stop sign and jamb hard on the brakes. If peddle goes to floor and you fly on through the intersection with no light coming on, you are an idiot

[Andy4639]

You can hook it up to be on if the e brake is set to. Very simple to do and will save your rear brakes if your bad about leaving them on.
Here is my thread on doing the e brake switch.

Tim your a funny guy!


http://67-72chevytrucks.com/vboard/s....php?p=7608320

[Gregski]

Originally Posted by CG

Where do these color diagrams come from? Id like to take some of them and redo in Illustrator (very time consuming) and make garage art that's also useful.

This is one very good thread by boundstaffpress, there may be others

Color Wiring Diagram FINISHED

[CG]

Thanks for that link. I had forgotten all about it!

[davepl]

Originally Posted by CG

Where do these color diagrams come from? Id like to take some of them and redo in Illustrator (very time consuming) and make garage art that's also useful.

There's a commercial firm that makes them, but I think these were done by someone on the board (edit: Boundstaffpress?). Someone colorized them and then I just joined them into one big image for convenience.

If Illustrator has a TRACE function that'll do the bulk of the work to get you close, a scalable one would be cool! You could scale it up and print it on your wall :-)

So, if you do it, please send me a copy!

[54blackhornet]

71 GMC 2500 should have discs up front

[54blackhornet]

Can anyone explain how to reset the brake light after you fix uneven brake pressure ? Both sides of MC are full but the light still glows ? Thanks

[jocko]

Originally Posted by 54blackhornet

Can anyone explain how to reset the brake light after you fix uneven brake pressure ? Both sides of MC are full but the light still glows ? Thanks

In Park, slam the pedal home as if doing a panic stop. If you have correct pressure range in both systems, it should reset. If not, you'll wizz some brake fluid out somewhere, likely a wheel cylinder. Just refilling won't fix a brake light issue - the cause of the pressure drop that caused one side to decrease has to be fixed - and you may have done that, just mentioning in case any folks new to brake systems might think a refill was the fix. I will be the first to admit, chasing down issues with the brake light are kind of a pain, and it's sometimes difficult to reset. There is another procedure in the manual that requires some specific/special (or homemade) tools.

[VetteVet]

Originally Posted by davepl

There's a commercial firm that makes them, but I think these were done by someone on the board (edit: Boundstaffpress?). Someone colorized them and then I just joined them into one big image for convenience.

If Illustrator has a TRACE function that'll do the bulk of the work to get you close, a scalable one would be cool! You could scale it up and print it on your wall :-)

So, if you do it, please send me a copy!

How much to ship a wall?

[CG]

Originally Posted by davepl

There's a commercial firm that makes them, but I think these were done by someone on the board (edit: Boundstaffpress?). Someone colorized them and then I just joined them into one big image for convenience.

If Illustrator has a TRACE function that'll do the bulk of the work to get you close, a scalable one would be cool! You could scale it up and print it on your wall :-)

So, if you do it, please send me a copy!

Illustrator does have a trace function, but its not perfect. I think if I was to do it I would just go over each line with the correct tools to make sure its perfect. And illustrator is infinitely scalable so you could paper your whole house I suppose haha. But it looks like someone already redid the first one on that thread and it looks really nice and printable.

I believe I asked the originator ages ago if he would share the AI file and he declined. I don't blame him, it was a lot of work. It really does take hours to make it perfect.

Over in the Photoshop section of this board you always see ... Oh this one was a quickie. It might have been a quickie, but only in Photoshop time. In actual time the quickies take quite awhile.

[Gregski]

Originally Posted by 54blackhornet

71 GMC 2500 should have discs up front

Not sure if this was meant for me ie the original Poster, but I have a 1500, and yes I know the '71 should have disc brakes already but this is a basket case and appears to sit on '69 chassis with 6 luggers and drums all the way around, just letting you know, it's a fun puzzle to put together for sure