ArdWrknTrk Posted February 2 Share Posted February 2 Jim - I'm sure my writing is a sign of sloppiness. Some have suggested that I should have been a doctor. But having literally JUST met with my doctor, I think I'm too organized for that. After we talked a while he said "So, you don't have any complaints. So, why are you here?" I replied that "This is supposed to be a Medicare wellness check wherein you ask me what county I'm in and if I have extension cords running across the floor in the house." He basically did a Ok, back to the questions, with my answers in bold: - circuit 848, “speed control switch return” Do I simply run that wire to ground as Gary suggests in the Big Blue thread? Yes. It works. - circuit 307, “brake pressure input” My master cylinder does not have provisions for this “fire hazard” switch. Do I cap this wire off? In essence creating the “open when system has pressure” state necessary to allow use of the controls? No. The switch opens when there is pressure in the brake system, so the speed control needs 12v on that circuit save for when the brakes are applied. Otherwise it won't engage. So if you don't have the switch then you need to take that wire to power, but you will lose a safety. - circuit 306, “clutch pedal position switch”. I will no longer have this switch so I’m assuming that I need to provide a jumper, out of a couple female spade terminals and wire, at the connector (as the EVTM diagram implies) Yes, or as Jim suggested with a fuse. - circuit 679, “vehicular speed input”. I would very much like to retain the use of my stock VSS that is part of my speedometer cable (just under the master cylinder) It has two wires, the DG/W would be the signal and the BK should be ground. Can I just run the BK wire over to the firewall with a ring terminal and a self tapper? Or does it need to be tied into the harness somewhere? You could ground the Bk wire, but I made a "twisted pair" by twisting the two wires together for the run to the speed control. That helps to cancel out electrical noise in the signal. But in my case I was running the wires from the transfer case instead of by the master cylinder, so my wires were a whole lot longer and, therefore, more likely to pick up noise. I managed to get by Staples on the way to work. (@3. 😉) I'll be looking at all this and trying to sort it out. Hopefully by dawn I'll have something to run by you and Bill, since I've never had speed control. Link to comment Share on other sites More sharing options...
85lebaront2 Posted February 2 Share Posted February 2 I managed to get by Staples on the way to work. (@3. 😉) I'll be looking at all this and trying to sort it out. Hopefully by dawn I'll have something to run by you and Bill, since I've never had speed control. Ok, the electronic vs vacuum speed control: 1. Steering wheel switches are the same for both 2. Vacuum system uses a dump valve or a pair of dump valves depending on whether it is auto or manual transmission. 3. These are the "fail safe" so if the electronics fail to cancel via closing the vacuum valve and opening the vent, the servo is vented so the throttle is released. 4. Electronic speed control uses a servo motor and an electric clutch to pull the speed control throttle cable. 5. Electronic speed control clutch is fed through the switch on the master cylinder, hydraulic pressure opens the switch dumping the clutch so that if either the servo is stuck or the electronics fail to disengage the speed control you do not have a "Chevy motor mount moment". To achieve the same safety function, a normally open (closed when depressed) switch on the brake pedal will serve the purpose. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 2 Share Posted February 2 Ok, the electronic vs vacuum speed control: 1. Steering wheel switches are the same for both 2. Vacuum system uses a dump valve or a pair of dump valves depending on whether it is auto or manual transmission. 3. These are the "fail safe" so if the electronics fail to cancel via closing the vacuum valve and opening the vent, the servo is vented so the throttle is released. 4. Electronic speed control uses a servo motor and an electric clutch to pull the speed control throttle cable. 5. Electronic speed control clutch is fed through the switch on the master cylinder, hydraulic pressure opens the switch dumping the clutch so that if either the servo is stuck or the electronics fail to disengage the speed control you do not have a "Chevy motor mount moment". To achieve the same safety function, a normally open (closed when depressed) switch on the brake pedal will serve the purpose. Thank you for this! It's where I was going when I glanced at the prints, but I haven't had time to think about it. Things were pretty hectic when I arrived Link to comment Share on other sites More sharing options...
mat in tn Posted February 3 Share Posted February 3 Ha! I’m not sure about that claim to fame. No rush, as today is being spent working in the woods, aka, drinking beer and burning logs that's my plan for tomorrow Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 3 Share Posted February 3 that's my plan for tomorrow Okay, I see these are largely answered.questions. Ground is right there.... Clutch interlock is a simple jumper (really simple, if you're using the bullnose cab harness) The damn firestarter master cylinder switch... 🤯 As I posted about my neighbor Ben's truck fire over a decade ago..... I don't think it needs hot at ALL TIMES, It could easily be power in start & run instead of constant. Closed except when brakes applied. We can figure out a way to rig this without the master cylinder that Ford screwed up. (or you could get one with the proper diaphragm material that won't go up 🔥 IDK about the bullnose speed input v/s my tone ring in the pumpkin. I guess it depends on how many pulses per mile the PSOM produces vs the Bullnose VSS. There are a million cheap solutions to this... Cheap ES32 chip to interpolate one signal to another output? I'm really not sure which harness you're using, or where it interfaces with the existing..? What else do we need to look at? Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 3 Share Posted February 3 Okay, I see these are largely answered.questions. Ground is right there.... Clutch interlock is a simple jumper (really simple, if you're using the bullnose cab harness) The damn firestarter master cylinder switch... 🤯 As I posted about my neighbor Ben's truck fire over a decade ago..... I don't think it needs hot at ALL TIMES, It could easily be power in start & run instead of constant. Closed except when brakes applied. We can figure out a way to rig this without the master cylinder that Ford screwed up. (or you could get one with the proper diaphragm material that won't go up 🔥 IDK about the bullnose speed input v/s my tone ring in the pumpkin. I guess it depends on how many pulses per mile the PSOM produces vs the Bullnose VSS. There are a million cheap solutions to this... Cheap ES32 chip to interpolate one signal to another output? I'm really not sure which harness you're using, or where it interfaces with the existing..? What else do we need to look at? The number of pulses/mile or revolution doesn't matter. The speed control just keeps the number of pulses that were being generated when you hit Set the same. But apparently the Bullnose pulses are the same as what was expected in the 90's as my speed control picks up or drops off 1.0 MPH each time that Set or Coast is hit. And you are right, the brake switch should never have had power all the time. Mine gets switched power and works great. And Bill is right, a switch on the brake pedal would suffice to get that safety back. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 3 Share Posted February 3 The number of pulses/mile or revolution doesn't matter. The speed control just keeps the number of pulses that were being generated when you hit Set the same. But apparently the Bullnose pulses are the same as what was expected in the 90's as my speed control picks up or drops off 1.0 MPH each time that Set or Coast is hit. And you are right, the brake switch should never have had power all the time. Mine gets switched power and works great. And Bill is right, a switch on the brake pedal would suffice to get that safety back. Two things Ford engineering screwed up. They drew the fuse on the trailing side of the switch. They speced Kapton for the diaphragm, and it's not resistant to glycol. The brake master switch could be plenty safe. And using actual hydraulic pressure is about the most failsafe way to do that. (still burned my neighbor's truck down) I told him. People don't want to listen to me. I had pictures, but Flickr went subscription and I 🤬 Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 3 Share Posted February 3 Two things Ford engineering screwed up. They drew the fuse on the trailing side of the switch. They speced Kapton for the diaphragm, and it's not resistant to glycol. The brake master switch could be plenty safe. And using actual hydraulic pressure is about the most failsafe way to do that. (still burned my neighbor's truck down) I told him. People don't want to listen to me. I had pictures, but Flickr went subscription and I 🤬 Right on all counts. You just have to gently touch the brake pedal on Big Blue and the speed control shuts off. Unfortunately Kurt doesn't have a switch on his master cylinder. Maybe this would be a good time to do the master cylinder upgrade? Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 3 Share Posted February 3 Right on all counts. You just have to gently touch the brake pedal on Big Blue and the speed control shuts off. Unfortunately Kurt doesn't have a switch on his master cylinder. Maybe this would be a good time to do the master cylinder upgrade? I don't know if the one I keep showing from uhaultruckpartsonline has the port. I know it's still listed but I don't think U-haul wants drivers being lazy Link to comment Share on other sites More sharing options...
Tarheel Blue Posted February 3 Author Share Posted February 3 Right on all counts. You just have to gently touch the brake pedal on Big Blue and the speed control shuts off. Unfortunately Kurt doesn't have a switch on his master cylinder. Maybe this would be a good time to do the master cylinder upgrade? I did the MC upgrade over 10 years ago. I installed an ‘87 version w/ the plastic reservoir so, I’m reluctant to change out my MC at this point Just to have a switch that seems redundant, because I think the stop lamp switch on the brake pedal serves the purpose of shutting off the servo. The ‘85 EVTM shows indicates that the stock stop lamp switch get 12v/ 15a at all times via fuse 1 and describes the function as “closed with brake depressed” In stock form, in 1985, there were only two things that could get the servo to shut down. 1 - touch the brake pedal 2 - touch OFF on the horn pad Am I missing something? Link to comment Share on other sites More sharing options...
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