What are these? What do they do?

[Free Candy Inside]

I mainly post in the 60-66 section for the 63 Panel truck I'm building but I have a tbi 350 with a 4l80e tranny that came from a 1995 G30 based RV in the truck as my drivetrain. I'm trying to wire all of the 95 harness into the 63 stuff. So far I have successfully wired up the ignition switch, I'm using the 95 headlight switch (it actually fit in the 63 hole in the dash and was very similar to the 63 switch), and have most of the turn signal stuff figured out. I am trying to eliminate all things that I don't need to make it run or are needed legally (turn signals, headlights, tail lights). I have unhooked wires like the radio for now to simplify things. I figure that will be easy enough to add later. I have 3 mystery items I don't know what they do. The vehicle did come with cruise control which I'm considering eliminating. All 3 of these are located by the steering column.

So here they are: First one was located by the drivers side kick panel. I thought maybe it was tied in with the parking brake?

[Free Candy Inside]

Second one. Also located by the kick panel

[Free Candy Inside]

Last one. This was located at the base on the steering column. It snaps on and has a tong that slides when the steering shaft is turned. It transfers power based on where the slider is. I thought it would be like a clock spring to turn off the turn signals but it doesn't.

[Free Candy Inside]

And here is a pic of all the wiring I'm trying to sort out. It does actually run and drive even with all this mess!

[87lm7]

The first pic is your brake light switch that also gives a signal to the ecm and cruise control, the second is the speed buffer I believe, and the third is your neutral safety/park-neutral switch. Hope that helps.

[ChevyTech]

Originally Posted by 87lm7

... the second is the speed buffer I believe...

Yes,
Also known as the DRAC

The DRAC conditions the alternating currant signal from the vehicle speed sensor to a square wave signal so it can be used by the vehicle electronics.

The DRAC also compensates for axle and tire size variations so the speed signal is accurate.

1995 model was the last year for a separate DRAC, in 1996-up it's built into the PCM.

The VSS produces 40 pulses per drive shaft revolution.
The DRAC uses an Schmitt trigger to convert the AC wave the a square wave
The DRAC produces 2000 pulses per mile signal for the speedometer
The DRAC produces 4000 pulses per mile signal for the cruise control
The DRAC produces 128000 pulses per mile signal for the antilock brakes

[Free Candy Inside]

Thanks guys and yes that's very helpful. Not sure how I can use that brake switch with my setup. Probably just have to wire it in to my existing switch. And I guess I can cut out the neutral safety switch thing as I'm running a Lokar shifter.

[87lm7]

The computer does need to see when the trans is in park/neutral and when it's in gear though, some limit the rpm's when they are not in gear so I have been told. The blue and green wires are for your back up lights and the other wire, I believe it is black with a white tracer, is the one going to the computer. I think it is grounded when in gear but it had been awhile since I've looked at a wiring diagram.

[ChevyTech]

Originally Posted by 87lm7

The computer does need to see when the trans is in park/neutral and when it's in gear though, ...

He is correct.

The IAC will not work correctly without that input.

If you can't get that brake switch to work with your pedal, use one a few years older. A single set of contacts like a 1963 had will not work.
The brake switch has multiple circuits through it. Notice all the wires. You need it for the transmission lock up torque convertor. The brake switch has separate circuit for cruise control also.

If you take short cuts and do not connect ALL the electronics it WILL affect how well the PCM controls the engine and transmission.

[Free Candy Inside]

IAC - idle air control? I'm doubting I'm right with that. I had an 84 donor truck that I used the front K member and master cylinder in my panel truck. I also put the brake pedal set in the truck to work with the master cylinder properly. The brake switch for it looks like it is 2 wires. Are you saying I need to use the whole brake switch from the 95?

[ChevyTech]

Yes, the IAC = Idle Air Control
You are right about that.
I am a little worried you are in over your head. But if you hook up ALL switches and sensors so they work, you will have no need to understand everything about the system.

The IAC (and computer) controls the idle speed.
The IAC (and computer) is what gives the engine a “fast idle” speed when started cold.
The IAC also supplies more air to compensate for the extra load when the A/C is on.

If you have the brake pedal & master for a 1984 K series then it will be easy to do.

There are a lot of square body trucks that had transmissions with lock up torque convertors which required a brake switch with multiple contact sets in it. I would use a switch from one of those. The square body trucks had brake switches that are way more dependable too. It seems like every truck GM built after 1987 had a weak brake switch in it.

The computer (PCM) controls the shifting of a 4L80E transmission and needs the inputs to do it.

You should get a schematic for the donor truck so you do not cross wires when wiring to a different brake switch.

You have the DRAC signal for the donor cruise control if you want cruise. If you do want cruise the square body trucks had a second brake switch for the cruise. The wires for that should be in with the brake switch wires in the donor harness. If you want the new style cruise you should be able to find everything you need to hold multiple brake switches too, but your setup may already have that.

[Free Candy Inside]

Thanks for all the info, I appreciate it. I would have to agree that I am in over my head on most of this wiring although I'm mainly just shortening things up and cleaning up the harness. So far I have everything connected as it came besides the brake switch. I guess I was thinking about this harness like my chopper where I only have the things it needs to run and drive. I probably should have used the donor steering column and made my life way easier but I wanted this thing to look factory from the outside.

[Free Candy Inside]

Do you think it would be easier for me to just do the transmission hack with 3 switches and just control it manually? I was considering doing that anyways.

[ChevyTech]

I like to keep things set up so my wife can operate them with up doing damage.

I would connect everything so it works just like a 1995.
With just a little work you can have that.
To me the electrical stuff is a very small task compared to the engine & tranny swap.

Us older people that drove vehicles with manual chokes, carburetors, freezing weather, and carburetor icing, forget the the new generation expect to get in turn the key and the engine starts and run well without any other action, like holding the gas pedal down a bit or setting the choke.

When I think of the older trucks, I remember my 1967 with 4:11 gears and the poor fuel mileage down the freeway. If I put together a old truck for a toy it will have overdrive and a lockup convertor.

[ChevyTech]

One more item I just thought of.

You should swap the horn relay in your truck.

When vehicles went to having computers with semiconductors in them, changes were made to other parts like the horn relay. Protection was built into the new horn relays so they do not induce a voltage spike as the magnetic field collapses across the winding inside it.

My understanding is that all horn relays with C4 molded into the outer cover have the protection diode inside them. Any car build starting in 1981 should have the protected relay.

[Free Candy Inside]

So I did a bunch of wiring today and I found that my brake switch has 4 connections on it. I hooked up the white and orange in the front (it still had the factory pigtail) and then I planned on putting the pink and purple wires on the back set or tabs. That still leaves me with 2 other wires. Guess I need to check a decent wiring diagram and see if I can daisy chain them together or if I have to add another brake switch.

Wire wise, I literally am using everything from the 95. I completely gutted all the 63 wiring. The only thing I am going to wire in is the turn signal switch from the 63 into the 95 harness. Other than that, everything else is 95.

[ChevyTech]

My guess, without looking at a 1995 schematic, is you have the brake lights wired, and the brake switch for the PCM wired. I think the other two wires are for the cruise.

None of these circuits should be daisy chained together.

[Free Candy Inside]

I haven't decided if I'm going to try to keep the cruise or not. I left the connector but since I'm not running the 95 steering column I don't gave the controls for it. I'm sure I could wire that up also but that can come later.

I know it's stupid but I went to get a chilton/Haynes awhile ago and it had like 30 pages of black and white diagrams. I hate those so I didn't buy it. If I could find a decent color diagram I would like to buy one. So far I have only shortened wires and untangled them so hopefully everything is still in working order as it came. I went wire by wire so I'm pretty confident all is good. I'm almost done. Finish it monday. Winter break as a teacher has its perks

[ChevyTech]

The service manual schematics from GM for 1995 are in black & white and not very good.

Every year the GM manuals get worse. I remember decades ago schematics in some of the service manuals that were in color and on a fold out page so a circuit could be traced through the entire vehicle. Now the schematics are in bits and pieces with to many mistakes in them.

To me Haynes and Chiltons manuals are worthless.

If you find one that is in color, and online, let me know because I will save a copy of it.

[Free Candy Inside]

I agree. I looked at the diagram and thought this won't even help so I didn't buy it.

[joecool]

Chevytech ,I sent you a message,thanks