How do I bleed the RABS valve on a 94 Mazda b4000

You always start with the brake that is furthest away from the master cylinder. On most vehicles, it is the passenger rear. Bleed until nothing but clear fluid comes out of the bleeder valve and make sure that the fluid does not go empty in the master cylinder reservoir. Then move to the next closest brake, usually the drivers rear, then to the next closest, usually the passenger front, then finally the last brake. If you do not end up with a proper operating brake system, there must be an issue in the system. Bad master cylinder, booster, or ABS system are likely suspects.

Kind of sounds like the torque converter might be locked up. This happened to me on my 96 dodge truck, my converted had exploded inside.

https://www.bing.com/images/search?q=2001+mazda+b4000+fuse+diagram&qpvt=2001+Mazda+B4000+fuse+diagram&qpvt=2001+Mazda+B4000+fuse+diagram&FORM=IGRE

Should be 30 - 40 psi at idle.

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The reason is, you have a rear anti lock brake system. The anti lock valve is located on the frame just underneath the brake master. It is called a RABS valve. Almost impossible to bleed. But it can be done. A dealer has a tool that plugs into the RABS valve which activates the valve constantly moving the valve back and forth. This will then push all fluid and air out of your open bleeder screws in the rear.
I did'nt go to the dealer. i was too stubborn. My solution was to lift the rear of the truck and place on jack stands. Pinch off the rubber brake hoses on the 2 front brakes with a C-clamp or non marring vise grips, this will keep all fluid from going to front brakes. Next adjust the rear brake shoes by tightening the adjuster on the rear brake drums. Tighten the brakes on the rear until the brakes start to drag and the tires no longer spin freely by hand. Attach a bleeder hose to the bleeder screw on the RABS valve, place open end of hose into a jar or canister of brake fluid, so as not to draw in any air. Open the bleeder screw. Start the vehicle up, put it in gear, and let the rear tires spin. (I got up to 25mph on my speedometer) Step on the brake while it is in gear and the tires are spinning. This will activate the RABS valve and cause the air in the RABS valve to bleed. Do this several times. Put vehicle in park, shut off engine, and close the bleeder on the RABS valve. Attach bleeder hose to right rear of the truck, place open end of hose in a canister or jar of brake fluid so no air gets in and open the bleeder screw. Start the vehicle up, put it in gear, and let the rear wheels spin freely. As the wheels spin, you press your foot on the brake pedal, this will activate the RABS valve, and effectively bleed the brakes. Do this a dozen or so times, tighten the bleeder screw and do the other side. Remove clamps from front brake hoses and you will be go to go. All this may seem a bit extreme, but it is the only effective way to bleed a Rear Anti Lock Brake System on an early Ford. All the steps I laid out are necessary. You cannot skip one. The reason why the rear has to be in the air, is that there is a sensor mounted to the rear differential that senses wheel spin(or axle spin), this goes directly to the RABS valve and tells it that the tires are moving at a certain speed, and to activate the Rear Anti Lock Brakes when the brake pedal is depressed. It will not activate if it does not sense movement. The reason for pinching off the front brake lines, is that there are needle valves in the master cylinder and they will send too much fluid to the front calipers, and stifle or hinder the amount of fluid needed to go to the rabs valve and ultimately the rear wheel cylinders. It seems like a lot, and it is, but I did it and it works. Good luck

SOUNDS LIKE IT IS A BLEEDING NIPPLE FOR BLEEDING BRAKE SYSTEM.

fuel cap

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In order to bleed the RABS there is a special tool that plugs into the connector of the RABS and holds the solenoids open to facilitate bleeding, you will need to take it to a brake specialists that has a tool to do this.

the nipple sticks out side the bell housing on the left side just above your hydralic line for your clutch,auto zones web has a complete diagraham and steps for bleeding