1976 non functioning cruise control

[duane_wong@hotmail.com]

I'm posting this problem in the general discussion section rather than the technical section because I see a recent , similar post here by fellow member Roy Schroeder . My 76 Eldo's cruise control doesn't work either . First , is the cruise control in my 76 the same set up as Roy's 78 ? If it is , I'll print out the responses to Roy's post , give the information to my restorer , and save everyone the time of repeating information for me .  Second , let me try to explain what my restorer has told me . This stuff is way out of my league , but I'm sure some of you will know what he is talking about . He said he thinks the problem may be in the "transducer" - a unit which is attached to the firewall that has a wire entering it from the transmission and another wire exiting it  and going to the speedometer . He said the service manual states that the "coil in the transducer "( his words , not the manual's -  I guess some people refer to it as a solonoid ) is supposed to register 6.0 ohms but mine registers only 0.5 ohm . I hope I'm relaying this information correctly . So ... does it sound like this unit might be the problem ; and if it is this unit , can it be repaired/rebuilt or must I go junk yard hunting ? I'm waiting for J. Pinto to respond to that same question in case someone planned to suggest his name . Thanks for any help . Paul Tesone CLC #6876

The whole story for me goes back to adjusting the brake/cruise switch at the pedal.
I think it has been misadjusted for some time,  not having tried to use it for months after installing the brake booster.

I had a 1976 Cadillac Seville that had cruise control that wouldn't engage. No green cruise light and no engagment with the cruise control switch turned on and tap the engagement button on the end of the turn signal switch above 24 mph.

After going through the 1976 Cadillac Seville troubleshooting in service manual, I found that my transducer was bad (according to the manual) using a test light and further utilizing continuity function on my ohmmeter.

According to the service manual, one can pull and rotate the two pronged hold/engage connector, and connect the the 'black' wire normally connected to the  'engage' connector to the 'hold' prong with the key ignition on and the cruise switch set to on, and depress the engagement button on the turn signal lever halfway, so you should hear the cruise control transducer click, and the green cruise light should light, until one depresses the brake pedal,  which should make the transducer click again and the green light should go off, signaling disengage of the cruise control.

I grounded the 'light' prong on the transducer to ground by backprobing the harness connector with a test light, and both the amber on and green cruise light came on on the dashboard switch for cruise control on/off switch, indicating a bad transducer (according to the service manual).
I also disconnected the small three wire harness connector under the dash with small black, brown, and blue wires on the end of the micro blue plastic colored plug that plugs into the black harness connector. I tested with a continuity function of my ohm meter with a couple of double ended small alligator clips from Harbor Freight Tools to test continuity with the button 1/2 pressed and fully depressed on the engagement switch on the turn signal lever. That tested out okay according to flowcharts in the repair manual.

If you can't see the contacts on the end of the blue plug, you can leave it plugged to the black harness connector and test the black receptacle by inserting the prongs of the ohm/continuity meter into the black, blue, and brown colored wires that enter the plug. One can test it that way, too.

I also tried to use a test light to supply power to the disconnected prong for hold and engage. No clicking sound.
I found a remanufactured/rebuilt transducer on ebay.com for about $200.

Update: I changed the transducer with a remanufactured unit, but it still did not cruise properly.

I am embarrassed to say, that I backtracked and found the brake light/cruise control combination switch was adjusted with too much play at the pedal. I had previously changed the vacuum brake booster out, and although the brake lights worked correctly, the cruise control portion of the switch was adjusted so it was sending a signal to the cruise control circuitry that the brake pedal was depressed, causing the cruise to not engage at all.

If I pulled up on the brake pedal and simultaneously 1/2 depressed the turn signal lever engagement button, and the green cruise light goes on momentarily, assuming the bulb is good, then everything is fine with the cruise control circuits except for the simple adjustment of the brake and cruise control combination switch.

In conclusion, my cruise control not engaging at all, can be traced back to a problem with adjusting the brake/cruise switch so the brake pedal barely rests on the button, as it returns under gradual spring pressure from the rod connected to the vacuum brake booster. It is better that the switch trigger brake lights and cruise control disengagement on an ounce of pressure pressed on the pedal by the foot, than to have it travel 1/2" before the brake lights go on and the cruise control disengaged. The brake/cruise disengagement switch on my car may eventually be replaced, but for now it works fine.

Note: I fixed the broken plastic vacuum T by replacing with a 5/16"  black plastic vacuum T from local NAPA Auto Parts store.

'Elementary, my dear Watson'- Sherlock Holmes comes to my mind.