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No Power to Transmission?

dabomb6608

dabomb6608

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Alright, i know theres another post up about the lockup. But i figured i would start my own thread so i dont hijack the other one. I gotta few questions. When i test the transmission for 12v on the A terminal. (1985 700R4) Do i need to have the truck running or just to the ON position? When i test it with it just in the on position it doesnt have any power. It has the vaccum switch behind the brake booster and the brake switch under the dash. I got ported vac going to the vac switch. Everything looks to be plugged in. My main question is where/how should i go about getting power to it? Is there a way to just run a hot wire to the brake switch only and then down to the tranny?
Thanks, Patrick
 
Thats what I did, found a switched power source in the fuse panel, ran a wire from that to the brake switch, from there to the trans. I cannot remember the terminal number on the trans on the 700r4, but in was the outside front side on mine. Power should go to it when the brake is not pressed.
 
Because the wiring is such a mess from the PO and i havent found much info when searching on how the original wiring is supposed to be. My haynes manual doesnt show it in the wiring diagrams.
 
It tells when your at a low vaccum(highway speeds, low load) correct? Then when it is under those circumstances it sends power on a "switched" 12v circuit to the tranny. The tranny also has a key on 12v wire i.e. A terminal only broke by the brake switch.


From another thread, posted by Blue85
There were a lot of variations of wiring inside the 700R-4. On the outside, there are generally two main circuits (pre-TBI models). You have a "constant" 12V, which is switched ignition broken only by the brake switch. Then you have a "switched" 12V which is broken by the brake switch, the vacuum switch and the 4x4 relay. This relay switches when the transfer case switch provides a ground. It lights the lamp on the dash and breaks this "switched" source to the tranny so that you only get lockup in 4th gear if you are in 4WD.

So if i could find out why the tranny and vac switch dont have power then i would keep the vac switch. But if not then i need to know how to wire it the correct way (like stock). Are there any wiring diagrams out there that show the tranny circuit?
 
dabomb6608 said:
It tells when your at a low vaccum(highway speeds, low load) correct? Then when it is under those circumstances it sends power on a "switched" 12v circuit to the tranny. The tranny also has a key on 12v wire i.e. A terminal only broke by the brake switch.


From another thread, posted by Blue85
There were a lot of variations of wiring inside the 700R-4. On the outside, there are generally two main circuits (pre-TBI models). You have a "constant" 12V, which is switched ignition broken only by the brake switch. Then you have a "switched" 12V which is broken by the brake switch, the vacuum switch and the 4x4 relay. This relay switches when the transfer case switch provides a ground. It lights the lamp on the dash and breaks this "switched" source to the tranny so that you only get lockup in 4th gear if you are in 4WD.

So if i could find out why the tranny and vac switch dont have power then i would keep the vac switch. But if not then i need to know how to wire it the correct way (like stock). Are there any wiring diagrams out there that show the tranny circuit?
Click to expand...

Correct about the vacuum switch...i'm not sure about the 2 different circuits though. If it's factory wiring it should go through the vacuum switch as well as the brake and 4x4 relay.
You'll need to back track through and see where the 12v is lost...it could be the brake switch not adjusted properly; could be the vacuum switch is bad...but remember, since the vacuum switch is connected to ported vacuum, it will not let 12v through it until the throttle blades open slightly like when in cruise; at idle it will not work unless you have it connected to manifold vacuum.
 
Ok well i have tested the wiring going to the vacuum switch before and it didnt have power going to it. I had followed the wires from the transmission into the cab. They go to a group of wires wrapped in the tape(im guessing factory) and then split three different ways. One goes up to the speedo. The other goes to a relay up behind the dash around the steering column on the firewall. And then the other goes to a big group that i havent found out where it goes.
Now the brake switch obviously is adjusted properly for the brake lights. But could it still be out of adjustment for the transmission side of things? Theres a connector on one end of it with 4 grey wires with black stripe on them. I unplug it and the brake lights still work. Are those the wires for the transmission?
 
I think those may be the ones..the relay you are referring to, is for the 4x4.
Mine had cruise control, and I think mine uses the switch that was for the cruise like the brake switch. It's right next to the brake switch. I had to adjust that one to make mine work. Does yours have that switch also?
 
Yessir. But cruise has been deleted. The switch is still there however and hasnt been touched. If i adjusted it should i adjust it to where it doesnt push the button until the brakes depressed? Or should it be barely on it? Im going to go look at it here shortly. Ive gotta get layerd up first, kinda chilly out there.

Edit: one thing i will add is when i put it in 4x4 the light doesnt come on on the speedo/fuel(whichever it is). I dont know if this is just a bad bulb or something related to this issue.
 
Mine was just the bulb in the dash...but remember that relay disconnects the 12v for the transmission; it's normally closed when not in 4x4, so is should still pass the 12v through it.
 
Ok well when I checks stuff for 12v earlier this week I can say that the relay had 12v going to it. From 1 wire
 
dabomb6608 said:
Yessir. But cruise has been deleted. The switch is still there however and hasnt been touched. If i adjusted it should i adjust it to where it doesnt push the button until the brakes depressed? Or should it be barely on it? Im going to go look at it here shortly. Ive gotta get layerd up first, kinda chilly out there.

Edit: one thing i will add is when i put it in 4x4 the light doesnt come on on the speedo/fuel(whichever it is). I dont know if this is just a bad bulb or something related to this issue.
Click to expand...

Pushing the switch should disconnect the 12v...so, if it's already pushing the switch in, it could be disconnecting the 12v.
Also, if you can find the wire that has the 12v from the distribution box, it would help to know if it's get 12v to the switch in the first place.
 
Ok well I'm outside looking and the brake switchs rest on it and then when you hit the brake the buttons springs out. I'm guessing it then makes contact when it springs out. I will adjust the white one to where u have to push the brake further. Glad I have an iPod so I can be on ck5 while working :)
 
dabomb6608 said:
Ok well I'm outside looking and the brake switchs rest on it and then when you hit the brake the buttons springs out. I'm guessing it then makes contact when it springs out. I will adjust the white one to where u have to push the brake further. Glad I have an iPod so I can be on ck5 while working :)
Click to expand...

Find the wire that should have the 12v that supplies to the tranny, then adjust the switch until you have the 12v, and then test pushing the brake pedal and it disconnects the 12v.
 
Alright well I adjusted it but couldnt test it for 12v. I am going to my dads to do that. Can test the lockup on my way over tho.
 
Ok no lockup. I tested the 2 wires going to the white brake switch. The brown one has power. Blue one never gets power when brakes is engaged or disengaged. I'm gonna try jumping them and see if the tranny gets juice.
 
We have the brake switch opened up. Cleaning up the contacts. Fixing he problem so now the question is. Why does the power from the brake switch give power to the front inside terminal on the transmission. I think it's "b" terminal. I thought the a terminal was the one with power all the time.
 
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