Brake Warn Lamp Wires

[Ppardini]

Hello everybody I've been lurking around this page for some time but have never posted, amazing the amount of knowledge on here! My 16 year old son and I are rebuilding a 1972 Chevy K20 for him. I have gotten tons of tips, tricks and answers from this forum. I have a question that I've searched for and found some parts of the answer but not the entire answer so here goes: installed a new painless wire harness hooked up a battery to it recently and just about everything works as it should, however I'm stumped on the brake warn lamp, I know that 2 brown wires are on the ignition switch one wires in to the master cylinder wire from engine compartment and one wires into instrument cluster harness, that's where I get confused every diagram I can find shows 1 brown wire for brake warn lamp coming off the instrument cluster harness but our original instrument cluster harness has 2 brown wires from this pin and I can't figure out for the life of me where to wire in the second wire. Any ideas would be greatly appreciated!

[pjmoreland]

That's strange. The only pin on the gauge cluster connector I've seen with two wires is the one with two gray wires for the gauge and heater back-lighting.

[Ppardini]

Well I wired it up without connecting the extra brown wire from the instrument cluster harness and the brake warn lamp works correctly so I have no idea what that extra wire is for, it's definitely factory so it had a proper use at one time.

[pjmoreland]

Originally Posted by Ppardini

Well I wired it up without connecting the extra brown wire from the instrument cluster harness and the brake warn lamp works correctly so I have no idea what that extra wire is for, it's definitely factory so it had a proper use at one time.

I suppose if you really wanted to know where it goes, you could remove the vinyl wrap from the harness. It can be unwrapped and re-wrapped afterward if you are wanting to preserve it. I have done this several times.

[RustyPile]

Originally Posted by Ppardini

Well I wired it up without connecting the extra brown wire from the instrument cluster harness and the brake warn lamp works correctly so I have no idea what that extra wire is for, it's definitely factory so it had a proper use at one time.

It's not a good idea to leave a disconnected wire loose in the harness. Do you have gauges or "idiot lights"? With idiot lights, there's a brown wire that runs from the external voltage regulator back to the instrument cluster plug. It's part of the charge light circuit. But it doesn't connect there with a second wire.. With gauges, this brown wire isn't there. Instead, it's the black wire with the small amp fuse, part of the amp gauge circuit. If you have an internal regulator, this brown wire goes to the alternator.

[Ppardini]

Originally Posted by RustyPile

It's not a good idea to leave a disconnected wire loose in the harness. Do you have gauges or "idiot lights"? With idiot lights, there's a brown wire that runs from the external voltage regulator back to the instrument cluster plug. It's part of the charge light circuit. But it doesn't connect there with a second wire.. With gauges, this brown wire isn't there. Instead, it's the black wire with the small amp fuse, part of the amp gauge circuit. If you have an internal regulator, this brown wire goes to the alternator.

It has an external voltage regulator, instrument cluster has a voltage gauge no idiot light and I have the 2nd brown wire out of the instrument cluster harness. So based off what you're saying I shouldn't have the 2nd wire? Maybe the only way to really know is when I get the truck fired back up if something is off with the voltage gauge?

[RustyPile]

Either way (gauges or lights) I don't see the need for the second wire. I'm not familiar with Painless wiring color codes, I'm going by the factory colors. First -- the wire that carries the brake warning signal isn't brown, it's tan. With the ignition on, voltage is sent to the brake warning light. The tan wire goes from this bulb to the proportioning valve. When there is a brake failure, a switch inside the valve grounds the tan wire and the warning light come on. The ignition switch has a built-in test circuit. Does the brake warning light come on when the ignition switch is in the "START" position?? Does the warning light come on when the tan wire is momentarily shorted to ground?

The brown wire I spoke of in my previous post is the charge indicator light. There are no other brown wires in these circuits. With gauges, the resistance needed to excite the voltage regulator is in a separate brn/blk wire. Due to my unfamiliarity with painless, I can't offer much more help. But I will suggest you take this up with Painless before you go forward with applying power anywhere.. Blown fuses, burned wires, and other damage could be the result.

[Ppardini]

I should've been more specific, yes these are tan wires and they are original cut and spliced off the original instrument cluster harness onto the painless wires. I took one of the tan wires and wired it to one of the small brown wires on the ignition switch the other small brown wire from ignition is wired to the master cylinder, the brake warn lamp works correctly, lights up when cranking the engine. Also the instrument cluster harness does have the black wire that runs to the alternator so I think I've got the voltage gauge connected correctly. So far so good no fires and no blown fuses. In hindsight I definitely should've paid more attention when I snipped all the wires off the original instrument cluster harness and followed where they went, I did not forsee a phantom extra wire.

[RustyPile]

Originally Posted by Ppardini

I should've been more specific, yes these are tan wires and they are original cut and spliced off the original instrument cluster harness onto the painless wires. I took one of the tan wires and wired it to one of the small brown wires on the ignition switch the other small brown wire from ignition is wired to the master cylinder, the brake warn lamp works correctly, lights up when cranking the engine. Also the instrument cluster harness does have the black wire that runs to the alternator so I think I've got the voltage gauge connected correctly. So far so good no fires and no blown fuses. In hindsight I definitely should've paid more attention when I snipped all the wires off the original instrument cluster harness and followed where they went, I did not forsee a phantom extra wire.

No offense meant, but just to inform you. You keep using the term "voltage gauge".. If you're referring to the factory gauge, it's not a volt meter that's used to indicate voltage.. It called an ammeter, and it measures a sample of the amperage, or current (not to be confused with voltage) that is flowing through the system.. I say "sample" because all of the current that flows isn't sent through that meter. Those 2 black wires with the small fuses are terminated near the ends of the main power distribution wire and form a shunt (parallel current path) and pass that sample through the meter, while most of the current flows through that large wire.. It's a safety design meant to keep heavy current flow out of the passenger compartment.

Now back to that "phantom wire".. As I stated, I'm not familiar with Painless wiring systems.. I don't know what deviations and liberties they took when designing their harnesses.. Since no one has come on here with an exact description of what that wire does or if some sort of modification is required, I'd seriously consider contacting Painless and ask them about it..

[Ppardini]

Originally Posted by RustyPile

No offense meant, but just to inform you. You keep using the term "voltage gauge".. If you're referring to the factory gauge, it's not a volt meter that's used to indicate voltage.. It called an ammeter, and it measures a sample of the amperage, or current (not to be confused with voltage) that is flowing through the system.. I say "sample" because all of the current that flows isn't sent through that meter. Those 2 black wires with the small fuses are terminated near the ends of the main power distribution wire and form a shunt (parallel current path) and pass that sample through the meter, while most of the current flows through that large wire.. It's a safety design meant to keep heavy current flow out of the passenger compartment.

Now back to that "phantom wire".. As I stated, I'm not familiar with Painless wiring systems.. I don't know what deviations and liberties they took when designing their harnesses.. Since no one has come on here with an exact description of what that wire does or if some sort of modification is required, I'd seriously consider contacting Painless and ask them about it..

No offense taken, thanks for the correction and the explanation. I've contacted painless they don't have an answer. The kit I bought is a 21 circuit with key in dash not specific to the 67-72 GM trucks although it is color coded to match GM vehicles.

[pjmoreland]

Originally Posted by Ppardini

I should've been more specific, yes these are tan wires and they are original cut and spliced off the original instrument cluster harness onto the painless wires. I took one of the tan wires and wired it to one of the small brown wires on the ignition switch the other small brown wire from ignition is wired to the master cylinder, the brake warn lamp works correctly, lights up when cranking the engine. Also the instrument cluster harness does have the black wire that runs to the alternator so I think I've got the voltage gauge connected correctly. So far so good no fires and no blown fuses. In hindsight I definitely should've paid more attention when I snipped all the wires off the original instrument cluster harness and followed where they went, I did not forsee a phantom extra wire.

So did your original harness have a total of three tan wires going to the gauge cluster connector? Normally there are just two (to two separate pins), and the second one is for the fuel gauge.

I'm not familiar with how the fuel gauge is wired on trucks with dual tanks, but I'm wondering if the extra tan wire could be for a connection to a second tank. Just a thought.

[Ppardini]

Originally Posted by pjmoreland

So did your original harness have a total of three tan wires going to the gauge cluster connector? Normally there are just two (to two separate pins), and the second one is for the fuel gauge.

I'm not familiar with how the fuel gauge is wired on trucks with dual tanks, but I'm wondering if the extra tan wire could be for a connection to a second tank. Just a thought.

Yes, there are 3 tan wires, a single on the fuel gauge pin and 2 on the brake warn lamp pin.

[RustyPile]

Originally Posted by Ppardini

Yes, there are 3 tan wires, a single on the fuel gauge pin and 2 on the brake warn lamp pin.

For the brake warning light to be tested when the ignition switch is in the start position, the tan wire must be switched to ground. Perhaps that second wire on that terminal connects to the brown/white wire on the ignition switch. I'd be tempted to give it a try using a jumper with small alligator clips.

[EDIT]They don't have an answer???? So it sounds like they don't know how their product is designed or works.. As I said, I build my own harnesses, but I don't deviate very far from the factory design. I can say this though: I know exactly how mine work. Give my suggestion a try. The warning bulb provides the load so there's not much chanCe of shorting something out.

[pjmoreland]

I think the original question was about an extra wire on the factory harness as opposed to an extra wire on the Painless kit.

[RustyPile]

Originally Posted by pjmoreland

I think the original question was about an extra wire on the factory harness as opposed to an extra wire on the Painless kit.

Yeah, that's the way I understood what he wrote, but I wasn't sure. That's why I elaborated on the possibility of the Painless harness being modified or somehow different from factory, so he should contact them about it..

In the idiot light harness, the brown wire coming off the charge light and the brown/white wire the the ignition switch pulls to ground when in the start position are connected to the same terminal on the inside plug of the firewall connector.. I wonder if it has something to do with that.. Possibly the truck came originally with idiot lights and at some point in the distant past a full gauge cluster was installed???

I can build a color correct harness for about 1/3 cost of these aftermarket assemblies, so I'm not familiar with their products.

[pjmoreland]

I think zosoppp has a valid point. The two tan wires that are normally crimped together at the ignition switch could have been crimped together at the gauge cluster instead.

[RustyPile]

Originally Posted by pjmoreland

I think zosoppp has a valid point.

HMmmm. It appeears so.. But the diagrams I have don't show those 2 tan wires connected to the switch.. On my diagrams, the tan wires from the brake proportioning valve (and the charge light when equipped) connects to the brown/white wire at the firewall connector. My diagrams are in a large GM issued book. The diagrams unfold from this book and are large enough to be easily read.. I was given these books when I attended a GM training school in Houston back in the late '70s-early '80s..

Although I don't recall ever seeing the tan wires actually connected to the ignition switch plug, connecting to either end of the brown/white wire doesn't affect the function of the circuit. If you guys are following my posts closely, you'll see where I suggested the OP do a test by temporarily connecting his "ghost wire" to the brown/white wire at the switch. it appears I owe zosoppp an apology.

[zosoppp]

Originally Posted by RustyPile

HMmmm. It appeears so.. But the diagrams I have don't show those 2 tan wires connected to the switch.. On my diagrams, the tan wires from the brake proportioning valve (and the charge light when equipped) connects to the brown/white wire at the firewall connector. My diagrams are in a large GM issued book. The diagrams unfold from this book and are large enough to be easily read.. I was given these books when I attended a GM training school in Houston back in the late '70s-early '80s..

Although I don't recall ever seeing the tan wires actually connected to the ignition switch plug, connecting to either end of the brown/white wire doesn't affect the function of the circuit. If you guys are following my posts closely, you'll see where I suggested the OP do a test by temporarily connecting his "ghost wire" to the brown/white wire at the switch. it appears I owe zosoppp an apology.

Whew, for a moment I was wondering if I'd misremembered.

No problem. We're all just trying to get it all sorted out.

[pjmoreland]

Here are some photos from a '67 dash harness for gauges that I've got. Sorry, the tan brake warn wire isn't visible in the last photo.

The '68 dash warning light harness in my truck had the "GENERATOR" light tan wire crimped together with the brown/white wire at the bulkhead connector like you described. I snipped the tan wire from that connection when I converted to gauges, and used the tan wire for one of the ammeter connections instead, along with the dark blue oil switch wire that was no longer needed for its original purpose.

[RustyPile]

Originally Posted by pjmoreland

Here are some photos from a '67 dash harness for gauges that I've got. Sorry, the tan brake warn wire isn't visible in the last photo.

The '68 dash warning light harness in my truck had the "GENERATOR" light tan wire crimped together with the brown/white wire at the bulkhead connector like you described. I snipped the tan wire from that connection when I converted to gauges, and used the tan wire for one of the ammeter connections instead, along with the dark blue oil switch wire that was no longer needed for its original purpose.

Modifying wiring harnesses and repurposing wires is all well and good for the person making those changes.. But what happens when some subsequent owner needs to make repairs?? Also, with all due respect to your knowledge and skills, pj, but the OP is working on a 1972 model, not a 67 or 68. I'm looking at an original GM factory diagram of a 1972 C/10, not some "universal" '67 - '72 diagram issued by some aftermarket 3rd party publisher.

Back in those days the mfgrs, especially GM, were famous for making mid-year changes.. There was a famous terminology used by all the parts guys. "Up to and after!!".. Referring to design changes implemented at a certain VIN sequence.

[pjmoreland]

Fair enough. And a future owner of my truck will have a lot more to worry about than just those ammeter wires being the wrong color. On the bright side, at least the ammeter works now as opposed to when I got the truck. The point I was trying to make, albeit poorly, is maybe you were looking at a warning light schematic instead of a gauges schematic.

[RustyPile]

Originally Posted by pjmoreland

Fair enough. And a future owner of my truck will have a lot more to worry about than just those ammeter wires being the wrong color. On the bright side, at least the ammeter works now as opposed to when I got the truck. The point I was trying to make, albeit poorly, is maybe you were looking at a warning light schematic instead of a gauges schematic.

This is what happens to discussions when a thread goes off on a tangent..

Read post #5 and #6.. I asked for clarification and the OP immediately responded.