brake lights work backward???

[williamM]

we were trying to untangle the dual circuit brake lights and found the return from the switch and hooked it up to the lights wire and the brake lights are on-- now when pushing the pedal- the lights are off. The signal from the brake switch is a double wire with 2 small "dash light" style connections with it. Can this circuit be combined with the warning light? to cold n dark last night for pics- going back after it now- and -- what might the alternator have to do with this circuit? as its not connected.

73 bus
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[Abscate]

Thats a great mod for keeping people off your a$$...
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[williamM]

good for brake checking big trucks
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some days I get up and just sit and think. Some days I just sit.

opinion untempered by fact is ignorance.

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[busdaddy]

There should be another thin harness with a black and black/red wire in it that leads to the fuse box and connector above the steering column brace. The wires you describe are for the dash warning light only, the charge light wire also connects to the warning light to "self test" the bulb every time you start the bus.
The terminal on the switches matter which wires go where as well, right now it sounds like you have some swapped, it should be the black (#15) wires on the 82a terminals, the red wires to the warning light on 81a and the black/red brake light wires on 81.
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[williamM]

Thanks- that makes it easier- was kinda annoyed that they worked backward and saw a post how some switches were wrong?? but this worked before we went after all the failed stuff under dash.
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some days I get up and just sit and think. Some days I just sit.

opinion untempered by fact is ignorance.

Don't step in any!

[williamM]

[Wildthings]

The brake switches as shown in Current Tracks #53-55 of this drawing are double throw switches, if you reverse the wires between terminals 81a and 82a, the switches will function the opposite of how they should.


Double click to enlarge:

[williamM]

We have spent a while with those wires and now have the warning light on the dash out of the circuit- locating the black wires at the fuse block has been a no show- power feeding them back from the fuse bloc has not produced any results except energize everything that takes ig voltage.

Today- we will power the fuse block and find the source for the switches and work backward from there.

NONE of the library of books really shows any of the connections clearly concerning the dual relays or how they connect to the warning lights or the brakes.

about to use shutters and coleman lanterns on strings.
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some days I get up and just sit and think. Some days I just sit.

opinion untempered by fact is ignorance.

Don't step in any!

[busdaddy]

There are no "relays" involved with the brake circuit, as WT's has mentioned all the action happens in the switches on the master cylinder.
The switches are powered by a black wire from fuse #12, it leads down the nose in a smaller black harness to 82a on the master cylinder (current track #55 on the diagram above). The 72 model uses the same circuit, perhaps this diagram below is more friendly for you?

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[telford dorr]

Sounds like the brake switch wiring is messed up.

The brake light switch is a single pole double throw switch. It has a common pole which connects to one of two terminals depending on whether there is hydraulic pressure or not. The switch common pole (81) connects to the brake lights. The normally open switch terminal (82a) receives power from the ignition switch. The normally closed switch terminal (81a) feeds the brake warning lamp on the dash.

The two brake light switches are wired in parallel, terminal for terminal. If both switches operate at the same time, the brake lights illuminate and the dash lamp does not. If only one switch operates, power feeds back from the operating switch through the non-operating switch and illuminates the dash lamp.

If the wires on the two switch terminals (81a, 82a) get swapped, then the brake lights will illuminate when the brakes aren't pressed and will go out when they are pressed. Check the switch wiring with a test lamp to see what's wired where. Test the disconnected switch with an ohmmeter to identify the common pole, the normally open terminal, and the normally closed terminal.

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[williamM]

wow- thanks guys- we have lights---ended up putting ben under the bus with a jumper and Leha running the brake pedal and found some mis placed connections (don't know who could have done such a thing) but did a methodical power track and ended up right where everybody said I would. So can't tell you what a relief it is to get yet one more process done. Pizza on me if you get to Quartzsite-- (ark Robbie if its any good.)




[img]

Guess who saw the Pizza first???[/img]
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some days I get up and just sit and think. Some days I just sit.

opinion untempered by fact is ignorance.

Don't step in any!