1977 superior/Chevy wiring

[Soundman1]

So the wiring on my bus is pretty shot and I am going to rewire the bus. I am using a universal harness. My question is about the electric brake override. I can not find a wiring manual for the bus and was wondering if anyone knows how the electric emergency brake stuff wires?

[chev49]

do you mean wiring that tells you that the emergency brake is on or wiring that puts the brake on.
ones i have seen have an idiot light that is on both when the switch is on, and the emergency brake is on so that the driver will not drive around picking up kiddies with the brake on all the time...

[Soundman1]

I'll start with a picture of the rear brake problem



Now some of the lights that come on. Oath the brake and the brake elect boost come on when I press the brake pedal



Now of the parts under the hood





And the brake pedal



The main questions are. What do you guys think the wires on the brake pedal feed?
What is going on under the hood what is the grey sensor wire? And what is the pump under the brake booster, how how does it all wire up?

And why is the electric brake boost light coming on?

[chev49]

its been over 25 yrs since i worked on one of these kind of systems. my first 1978 bus had about the same thing.. and a line going back to the rear brakes was also broken...so i jacked up both ends and changed all wheel cylinders and the brake lines.

first, with the wiring exposed, if it hooked up to something, either the color code of the wiring or using the VOM should tell easily tell you.
my guess for now is that one set of wires from brake petal sw goes to the stop lights, and the other to the booster. it looks like about the same color of wire goes to the hydraulic switch which is normally a stop light switch. that wire doesnt look so good on the end from what i can see.

it also looks like the booster has been changed out as well as the hydraulic lines.
i have yet to figure out why the red wire is grounded.. and where does the black one go to?
you should at least have voltage to one side of the brake switch wires..
if it were mine, i would start with that, and first determine stop light system working, then trace the 2nd switch set next. if you have nothing and are building your own wiring, just buy an aftermarket fuse panel with modern fuses and maybe some relays for the heavier load electrical stuff.

[Soundman1]

That's part of the problem, none of it really works so I am afraid previous owners jacked with it. There are some wires that when I follow them have a connector that has a resistor inline with it now.

I guess I need to keep hunting and find a wiring diagram, there has to be one somewhere

[Soundman1]

I found this wiring diagram

http://www.faxonautoliterature.com/1977 ... 26468.aspx

Just need to wait for it to show up n the mail now

[Soundman1]

So is it two seperate systems, and the electric is just there for a backup?

[ol trunt]

Wow! No kidding someone jacked with the brakes! '49's recommendation that you replace the wheel cyls and the (steel) lines is the first thing you need to do. There are two important factors in that repair.

1) Do NOT use compression fittings on any part of a hydrolic brake system--simply stated, they fail. No auto mfg anywhere in the world uses compression fittings on their product. There are two reasons for this; A, they fail, B, they cause a constriction in the brake line and as you know hydrolic pressure ALWAYS seeks the path of least resistance. A constriction even ever so slight provides added resistance. This results in fluid flowing to another part of the system faster than to the part of the system beyond the constriction. The faster the fluid arrives say at a wheel cylinder the sooner that wheel cyl can stop the wheel it serves. It is only going to amount to a split second before pressures equal out but that split second is enough to throw the vehicle into a one wheel skid from which recovery may not be possible.

2) Do NOT use a single flare flairing tool when you make up new brake lines. Double flare flairing tools used to be very hard to find. Now days they can be bought on line at several hot rod sites and even e-pay. The problem with single flares is that they tend to split the steel lines at the outter edge of the flare (right along the welded seam of the pipe). This leads immediately to difficulty bleeding the system followed by leaks around the joint. Once again, no auto mfg anywhere in the world uses single flare brake lines.

I can only add one thing to the discussion of your wiring issues. The tan or greyish single wire with the round plug (and the bare wires) is no dout supposed to be connected to the brake proportioning valve originally on your vehicle. If you ground this wire (ign on) the "BRAKE" light warning on the factory cluster should light. Wait until you receive your wiring diagram just to double check my suggestion before you ground the tan wire. Good luck !