Brake light switch /w cruise control fix

thethee

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Last couple of days I've been working on trying to get my cruise control working again and found that in fact the cruise part of my brake light switch had gone bad. When looking online th non cruise switches are readily available, but the cruise ones are hard to find. The one NOS I found was 125$ and that's just too much for me. So I figured I'd give it a go and try and fix my switch, even though its another one of those non servicable parts, and provide some pictures of the internals for the rest of you and show how it works.

This is from my '75 Imperial but I think the switch is used across many years and models. Don't mind the cut wire, that was me and I'll patch it later.
upload_2021-8-4_10-59-26.png


The blue wire connectors are mounted on the cap of the white plastic housing. The cap is glued on but with a sharp slim knife I was able to break the connection cleanly by being careful and going all the way around and not just force it at one end.

Components:
upload_2021-8-4_11-5-32.png

Center white stalk operates both switches simultaneously. Normal condition is pushed in with open circuit in break lights part and closed circuit with cruise control part. When pressing brake pedal switch is extended closing brake circuit and opening cruise circuit.

Cruise:
upload_2021-8-4_11-12-46.png
upload_2021-8-4_11-11-49.png

Brake:
upload_2021-8-4_11-13-42.png
upload_2021-8-4_11-14-10.png


The first problem with cruise part of the switch was center stalk, you can see some spots on the narrow right side. Plastic deteriorated so that it was out of round causing cruise circuit to be open all the time. Sanding it down with some fine grit sanding paper was enough. Second issue was that somehow, on the cap, the copper rivet lost it's connection to the brass wire connector. Some soldering fixed that.
upload_2021-8-4_11-16-9.png
upload_2021-8-4_11-18-15.png


Hope this helps anyone with a broken cruise control switch.
 

Ross Wooldridge

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Really cool diagnosis and repairs, well done! I'm in the process of designing a retrofit to install cruise control in cars with manual transmissions, and there a number of versions of that dual function brake switch out there - I think I found a Neihoff one for 15 bux that works, using the exact operational design - closes the brake circuit and opens the cruise circuit.

My biggest challenge was to make a bracket that held a momentary push button switch that I could mount on top of the clutch pedal - so the when the clutch pedal was in the up position the arm would press on the switch and would complete the circuit allowing the cruise control to function, but whenever the clutch pedal was depressed it would break the circuit and disengage the cruise until the clutch pedal was released.

After much fiddling on my workbench I got things so that it works, and that the bracket is adjustable. I used a heavy-duty hardware store black push button switch, that can handle up to 20 amps at 600 volts. So it's big and bulky but should stand up to the rigors of use.

Please keep me posted as to whether the repairs on your brakes which have allowed your cruise system to start working again - because as I delve into expanding my Auto Pilot repair services to include the refurbishment of vacuum control cruise control system, I'll likely be tapping you for some advice and tips.
 

Big_John

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I broke the switch on my car when I was putting the column back in. I found a $40 replacement so I was good, but I had also had figured that a regular $15 switch with a $10 relay could do the job.

You would wire the relay normally closed, with power breaking the circuit. Brake lights come on, relay opens the circuit.

The relay would also need to be under the hood, so the clicking "on and off " wouldn't drive you crazy, but it's all simple stuff.
 

thethee

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Really cool diagnosis and repairs, well done! I'm in the process of designing a retrofit to install cruise control in cars with manual transmissions, and there a number of versions of that dual function brake switch out there - I think I found a Neihoff one for 15 bux that works, using the exact operational design - closes the brake circuit and opens the cruise circuit.

My biggest challenge was to make a bracket that held a momentary push button switch that I could mount on top of the clutch pedal - so the when the clutch pedal was in the up position the arm would press on the switch and would complete the circuit allowing the cruise control to function, but whenever the clutch pedal was depressed it would break the circuit and disengage the cruise until the clutch pedal was released.

After much fiddling on my workbench I got things so that it works, and that the bracket is adjustable. I used a heavy-duty hardware store black push button switch, that can handle up to 20 amps at 600 volts. So it's big and bulky but should stand up to the rigors of use.

Please keep me posted as to whether the repairs on your brakes which have allowed your cruise system to start working again - because as I delve into expanding my Auto Pilot repair services to include the refurbishment of vacuum control cruise control system, I'll likely be tapping you for some advice and tips.
With this my speed control servo should be good as new, electrically speaking that is. I'm a little skeptical that the diaphragm will hold vacuum as I fixed a small hole with a bycicle tire repair set. Maybe it works, maybe it won't, will have to wait and see.

Had two other little problems with the servo 1) red wire on the right was touching the copper contact when it was flat so wouldn't activate vacuum dump valve and 2) vacuum inlet was pushed in to the servo so far it blocked off all vacuum all the time. Hopefully now it'll work, I'll keep you posted
upload_2021-8-4_16-6-8.png
upload_2021-8-4_16-7-52.png
 

thethee

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I broke the switch on my car when I was putting the column back in. I found a $40 replacement so I was good, but I had also had figured that a regular $15 switch with a $10 relay could do the job.

You would wire the relay normally closed, with power breaking the circuit. Brake lights come on, relay opens the circuit.

The relay would also need to be under the hood, so the clicking "on and off " wouldn't drive you crazy, but it's all simple stuff.
Agreed, there are several ways to fix it, but I really enjoy taking apart broken things to try and fix them. Even if things aren't supposed to be taken apart.
 

NY69

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Thanks a lot for taking the trouble to explain.
Question: how did you figure out that the switch was bad?
 

thethee

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With my multimeter I checked the voltage outputs of the wiring connectors in the engine bay. One was hot with CC switch in on position, one was hot when set or resume button was pressed and cold with buttons released, and third one did nothing. From wiring diagrams found that third one was connected to brake pedal. Checked third one for voltage while pressing and releasing brake pedal, nothing. Checked it for continuity with ground while pressing and releasing brake pedal, nothing. So switch must've been dead.

Removing the switch isn't easy.
 

thethee

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Refitting the switch was a pain.

Roadtest will have to wait since I need to renew my drivers licence first so don't know if it'll fully work BUT electrically everything is up and running. Had to also rewire control switch on the turn signal lever, wires were shot at the base where it screws into the column.
 

thethee

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Please keep me posted as to whether the repairs on your brakes which have allowed your cruise system to start working again - because as I delve into expanding my Auto Pilot repair services to include the refurbishment of vacuum control cruise control system, I'll likely be tapping you for some advice and tips.

My speed control is working again! Well, sort of. Setting a cruise speed caused it to accelerate, more than I expected, so I quickly turned it off before it settled. But it definitely engaged so I'm calling it a win. Feels like it needs some fine tuning, but that will have to wait. Me not servicing the wheel bearings caused me to break down this weekend so I need to sort that mess out first. You win some you lose some I guess.
 

Ross Wooldridge

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Glad to hear of your success - however, acceleration (uncontrolled) is indicative of another issue, so it's worthwhile looking into that once you're ready to.

It may be within design specs however, as I know that on my Perfect Circle electro-mechanical Auto Pilot system, if one turns the speed dial to increase the speed dramatically (say from 40 miles per hour to 80 miles per hour), the car will accelerate with vigour.
 

thethee

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Couldn't agree more! Definitely not there yet but on the right track at least.
 

thethee

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It is indeed accelerating continuously, it won't settle on the set speed. BUT I have a hunch of what's happening.

As posted earlier, the main vacuum control lever was wedged between the housing and the vacuum inlet port:
upload_2021-8-4_16-7-52.png


I pulled out the vacuum inlet port so the lever was free to move again. If I understand correctly how the speed servo works, when the car speed exceeds the set speed the lever is supposed to close the vacuum inlet to reduce vacuum pull on the throttle and reduce road speed. I think I pulled out the vacuum inlet to far so it can't be closed off anymore. But I also think the distance between the two is super important.

@Ross Wooldridge could you perhaps get me a measurement of how far the vacuum inlet is supposed to be pushed into the housing?
 

Ross Wooldridge

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@thethee - unfortunately I can't answer that question. My expertise is firmly in the earlier electro-mechanical units. However, perhaps the info is contained in the Master Tech document that is linked in other cruise control threads here on the forum - I'll see if I can find it...

Update - I can't seem to locate it right now - however, if you PM me, I'll send it to you. It's a large file but has a ton of info on the vacuum controlled auto pilot system.
 

thethee

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I have that master tech document. Unfortunately not mentioned in there but that makes sense as it's not supposed to come apart.

Was hoping someone knew a rough estimate but looks like some old fashioned trial-and-error will be needed.
 

Ross Wooldridge

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Make sure that sufficient vacuum is present in the first place, because I assume that the vacuum is not present (or low) to cue acceleration, and the reverse to close the circuit.
 
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