Topic: 1979 cruise control wiring question

[rerun]

My friend Matt has been restoring his 1979 Trans Am (403 Olds engine) for about a year.  It's now basically done, so it's time to address the one thing that doesn't work: the cruise control.  The car has new cruise control and speedometer cables, and the speedometer and tach both do work correctly.

I attached 3 photos to this post, and tried to embed below, but in case they aren't visible, see them here: http://www.gregburrus.com/1979/cruise
 
Under the hood we found a large bundle of green wire running along the top of the left fender. 



It runs from the firewall to the cruise assembly "HOLD" terminal.  As you can see, the wire has been folded back onto itself 10 times, with each loop about a foot in length. 



What really caught our attention was that the wire bundle was warm to the touch with the key ON, engine OFF.  There was 12 volts present on the green HOLD wire, and no voltage present on the black ENGAGE wire (also, there's no continuity to ground on the black ENGAGE wire, if that matters).



I believe that the cruise control harness gets its power from the spare ignition terminal on the fuse block.  As such, I guess it's normal for the wire to have voltage with the key on, and subsequently, the wire bundle could get warm.  But why would there be so much wire bundled and taped together - is that normal?

Also, I checked the fuse for continuity (pink/black wire) coming out of the fuse block and it tested good.  After going through the firewall into the dash are the green and black wire connect to a 3-wire connector (brown black blue).  This is as far as we have gone with our cruise control research.

Since the cruise isn't working, and the fuse I found at the under-dash fuse block was good, I imagine it could be any number of things: failed cruise button, faulty cruise system itself, etc.  The brake lights do work, in case the functionality of that switch impacts the vacuum breaker switch.

The RPO code for his cruise control system is K30, in case that helps (I don't know the visual difference(s) between Cruise Master and non-Cruise Master).

Please realize I'm not trying to get an answer/solution to why the cruise doesn't work - just trying to get some info about this huge bundle of green wire.

Thank you very much!

-R

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[Mongo]

The bundle of green wire is most certainly NOT stock.

[RENOVATIONS]

Actually it is factory correct so don't sweat it...all of my cars with cruise have this large wire "bundle"...older models use a brown wire but others have the green wire.

It's my understanding that this extremely long wire was GM's method of creating resistance in the circuit...for whatever reason 

[Mongo]

Really?  Didnt see that on mine thats why I made the comment. I may have to look again.

[RENOVATIONS]

Here's a pic of it on a '76 (brown wire on this one)

[Mongo]

Mine has a piece of plastic wire cover over it. That may be why I didnt see it. Leave it to the General.

[Gunner]

It's my understanding that this extremely long wire was GM's method of creating resistance in the circuit...for whatever reason  

GREAT engineering solution. 

Gunner

[rerun]

Thank you to Renovations and Fredbo99 - now that the green wire mystery is solved we can move forward with our diagnosis.  Thanks again!

-R

[r1mcnally]

Okay, I just learned a bit more about the cruise system.  I'm sorry if this is something everyone already knows, but I wanted to share in case it helps someone else.

Assuming you're driving faster than 30mph:

1. when the cruise button is pressed all the way in (the switch "off" position) any previous speed setting is lost, as this position interrupts voltage.
2. when releasing the button it first passes the "engage" position and voltage goes to the wire running to the cruise unit's ENGAGE tab.
c. when the button is all the way out (after you've pressed and released the cruise button) it's at the "hold" position and voltage will also now be found on the HOLD wire.

So putting this all together, when the cruise button is pressed all the way in ("off") there should be no voltage on the HOLD wire or the ENGAGE wire.  When the button is partially pushed down ("engage") there should be voltage on the ENGAGE wire.  When the button is completely released ("hold") there should be voltage on the HOLD and ENGAGE wire. 

If the above tests are good, we'll next check the contacts on the cruise-related switch located near the brake light switch down at the brake pedal.  When you hit the brakes the contacts of that switch open and voltage to the HOLD and ENGAGE wire is interrupted. 

We'll check these wires for continuity (as I can't test them very well while I'm driving down the highway) and see what we find.  We'll also likely replace all the vacuum hoses as they're probably original (and likely dried out and possibly cracked).  Wish us luck!  Thanks again to everyone for all your help.

-R