specialty wiring question: brake pressure switch (1 Viewer)

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Here is my wiring I made for the pressure switches.
Where does that single wire leading through the firewall plug into?

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All of the wiring for the low brake pressure and park brake switches is built into the 1971 OEM harness.
On your 1971 you should have a single Red, Green or Green/White wire coming out of the main harness that runs along the drivers fender. It will be in between the dimmer switch wires and the Vacuum Switched Valve connector. You would attach your Yellow/Green wire to that red or green wire. If you turn on the key and ground that wire, the Low Brake Pressure light will light up IF you keep your foot off the brake pedal so it does not build pressure. Once pressure is built up in both the front and rear brake circuits, the two low brake pressure sensors will OPEN turning the light off.

The hand brake switch on a 1971 is connected in parallel with one of the two sets of contacts on the 4 wire brake switch. If you look at the harness side 4 pin FEMALE brake light switch connector under the dash, you will see that there are 6 wires going into it. Two wires (Green/White and Green/Red) are for the brake light set of contacts and the other 4 wires (all Red/Whiteor all Green/White) are for the second set of brake switch contacts. Here are what the 4 wires do: low brake pressure switches (1 Red/White Wireor Green/White), park brake switch (2 Red/White or Green/White Wires) and 1 wire for the low brake pressure light (1 Red/White or Green/White wire) I attached a drawing showing how all of this is connected on a 1972 FJ40 identical wiring to your 1971.
Brake_ParkBrake_Low_Pressure_SW.jpg
 
Last edited:
Coolerman
I looked in the drivers side of the fender on my cruiser. And I didn’t see a R/W or GW as you mentioned . All I saw was two sets of blue/W wires.
These wiring harness’s on these trucks sure play games with you. My rig is an April/71.
 
Maybe it got broken off - were you able to dig around in the harness for it, otherwise just ruin a new wire from the brake switch
 
This is one of the most common repairs I make to harnesses that have the Low Brake Pressure Sensors installed.
That wire has a tendency to break off right where it enters the harness making it difficult to find. Untape that section of harness and you will find the wire.
 
This is one of the most common repairs I make to harnesses that have the Low Brake Pressure Sensors installed.
That wire has a tendency to break off right where it enters the harness making it difficult to find. Untape that section of harness and you will find the wire.
Your talking about undoing the harness at the drivers fender? Correct?
 
Ok
Now!
Another problem has reared its ugly head.
I go to Turn on the my hazards switch while the car is off. And the fuse blows right away the one tucked up under the cowl vent.
The thing I have changed was the turn signal switch and stalk from Spector Offroad.
Also, I hit the left turn signal and it blinks the fender light blinks and the indicator comes on at the dash.
I hit the right side I hear it flashing but the turn signal don’t light up at the fender nor does the indicator light up.
Driving me nuts.
 
Did the turn signals work before?
None of the right hand signals flash at all (front, rear, and panel light not even dimly lit), but the relay clicks?
Sounds like you might have a short to ground on the right circuit.
Does the fuse still blow if the column switch is unplugged?
 
Did the turn signals work before?
None of the right hand signals flash at all (front, rear, and panel light not even dimly lit), but the relay clicks?
Sounds like you might have a short to ground on the right circuit.
Does the fuse still blow if the column switch is unplugged?
They were working kinda! I had an old original turn signal switch that was very wonky. It would work at times other times it wouldn’t.
I finally gave in and bought a new one. Installed it and it worked great. Then it started not too. And this is what I am getting now!
 
Note: I checked all my bulbs and they are all good. I know this is the sound of a blown bulb but I did verify they were all good.
It also does it on the right side as well. 🤨
 
There are so many variables involved with the early turn signals/Hazards, they can be quite difficult to troubleshoot.

Start with the basics.
If ANY of your turn signal lamps are LED you MUST use an LED flasher!!! That fast flashing I hear could be a sign of LED bulbs installed somewhere or it could be a sign of a bad flasher. First thing I would do would is to swap in a know good flasher

Next I would pull the Hazard switch, take it apart, clean all the contacts, and re-lube it. When reassembling make SURE you get the metal tabs holding the phenolic contact board down tight, or you will have intermittent issues. I use a vice to crimp those tabs down tight. Dirty contacts in the Hazard switch can cause all kinds of weird issues.

Next I would verify that you have the new turn signal switch connected to the harness properly. It is VERY easy to get the turn switch bullets connected to the wrong wires on the harness side. Toyota knew this and provided a means to identify the wires easily.
The shorter two wires (Green/Yellow and Green/Orange) coming out of the OEM turn switch are for the FRONT turn signals. They plug into the triple bullet connectors on the harness side along with the dash turn lights. The longer two wires (Green/Yellow and Green/Orange) on the turn switch are for the rear lights.
Again, the triple female bullet connectors on the harness side are for the front turn signals and the turn signal dash lights.
Then I would check to make sure you have the right bulbs installed. Since the flasher is a current activated device, it has to have a certain anount of current flow before it will flash. Using the wrong type bulbs (ones with less current flow ie dimmer bulbs) can cause the flasher to not activate. Make sure the two sides are running the same bulbs front to rear.

Grounds
Since the 1970 lights rely on a basic metal to metal method of grounding, if they are rusty you will have an issue with current flow resulting in dim lights and/or no flashing. I would HIGHLY recommend you run a separate 16ga White/Black ground wire to each light housing and ground it to the frame or to the body. This ensures you have a proper ground for the lights. Also check for corrosion in the bulb sockets themselves. A Dremel tool and a wire wheel can clean those up in no time. Note: the dash turn indicator lamp sockets ground to the dash through metal to metal contact. Make sure they have good contact with the dash. You can also solder a ground wire to the lamp socket and run that to a bolt under the dash for a better ground for these two lights.

Fuse Blowing When activating Hazard Lights
If your rear chassis harness is mangled, you may have a short in the rear harness. To test this unplug the rear chassis harness from the main harness under the hood at the passenger side firewall. Then test the hazard lights again. If they work then you know the issue is in the rear harness. If it still blows the fuse then the issue is in the front wiring somewhere.
 
Ok
Went out (Spector Offroad) and purchased a used original flasher unit on the 40 series. Installed it and it works!
Now for the hazard switch.
Will take it apart and clean it up as per Coolermans instructions.
 

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