I think that the connector on the sensor might need to be replaced. It could have a bad connection inside. I think that LMC Truck or National Parts Depot has it. It should be pre wired and just require being wired to the existing wires. If you do this solder it or use posi locks (made by swenco) connectors. You can get these at Autozone and Walmart. Don't bother with the crimp ones or you'll end up having to crawl back under there and redo them.

 

ok. i checked the codes on yellow rear anti- lock light. it flashed 4 times. we did it several times, still 4 flashes. changed the rear abs valve on the frame under the drivers side. light still on. the yellow light stays on but doesnt flash at all when i ground it. it just stays lit. again ty
bill

 

i sure wish i knew how them 3 wires that go in a connector that goes in the master cylinder go. they had came loose sometime. i had changed them around to get my emergency brake light to go out. it went off when i released it. and all else seems to be working ok except the yellow rear anti brake light. again ty
bill

 

Bill,

On mine the center wire is black, with a purple w/ white trace front and rear

This is how mine has been acting for a long time.
I'm glad to hear that yours was flashing, and then started staying on. It gives me some hope that my computer isn't toast.......

 

when i turn the switch on now, it goes off momentarily then right back on. thats the way it has done all along, but still no flashing when i ground it, it just stays lit. ty
bill

 

Code 4 indicates a problem with circuit 535 (Light Blue/Red wire that goes from the RABS valve to the RABS Module. Code 4 is set when the RABS Module indicates the Valve Reset Input line to the RABS Valve has low resistance when it shouldn't.

For a code 4 this is the trouble shooting procedure.

Disconnect the 4 wire electrical plug at the RABS valve.

With an ohm meter measure the resistance from the pin shown in the diagram to the RABS valve body itself. Should measure greater than 10k ohms. If less, replace the valve.




If that test is okay this is the next test to perform.

Use an ohm meter and measure across the two pins shown in the diagram.
If less than 10k ohms, replace the valve.



Since you've already replaced the RABS valve the only thing left would be to do the last two tests.

Use an ohm meter and at the 4 pin connector at the RABS valve harness, you should measure zero ohms from the Black/White wire to ground.

Disconnect the negative battery terminal.
Disconnect the electrical connector at the RABS Module under the dash.
Use an ohm meter and measure the resistance of the harness connector Pin 6to chassis ground.

If resistance if greater than 100K ohms Replace RABS Module.
If resistance is less than 100k ohms, repair short in Light Blue/Red wire from RABS Valve to RABS Module.



This is a picture of the RABS Module located under the dash behind instrument panel left of center.

 

I have an 87 f250 4X4 and it has the rabs speed sensor on it as well. and like purecty my anti lock light is on. however according to my haynes repair manuel f series trucks and broncos didnt come equipted with rear anti lock brakes until 93. so obiously the book is incorrect.

 

well i guess i'll quit messing with mine. too much trouble for an old man. thank you guys for all the inputs. you have been great, again ty.
bill
and yes the book is wrong

 

The book is not really wrong....
My '80-'88 F Series Haynes manual shows the RABS in the schematic.

There was RABS that came out first, to try and keep boneheads from swapping ends when they panic braked in their unloaded truck.

True ABS was introduced later (1993?).
And *actually worked*, from what I'm to understand....

Sorry this has been so frustrating for you Bill.

 

thanks a lot friend for caring. im used to being frustrated as im an old fart and not much knowledge at stuff like this. but at least all the info u all gave me has been great, and i didnt screw up anything else while trying to fix this as i usually do. i can put one washer in a faucet and wind up having to re-do all my plumbing in my house. lol j/k there, but i can mess up a lot, so i think i better stop while my truck is still running. lol, its hell to be old and not much money to get things fixed. i love my truck, but i cant afford another one, so i'll just look at that yellow light. lol again ty
bill

 

Well sorry for resurrecting the dead.... But this thread was a pretty good one on the older truck RABS braking diagnosis. Yea I have been doing some digging. Not that I need the Rabs working. I am more of one to not like to stare at a idiot light on the dash. Yea pull it, but i would rather fix something right.

BTW my truck is a 1988 F250 4x4.

Just a couple foot notes for any others that follow in my steps.

When you check RABS codes on the 87-92? Fords, (The connector on the early ones are by the parking brake, the later ones are by the glove box. Small kind of square black connector)

Turn the key to on. The light should come on and go out, then come back on again if it sees a malfunction.

To read the codes, hook a jumper to a good ground, the bare metal of the parking brake pedal mount is a good spot. Turn the key to on (not running) and then touch the jumper to the end of the diagnostic connector. Only for a couple seconds and release. The light should start flashing. The code is fast but repeats itself over and over. So you can keep recounting to be sure.

BTW the RABS module is in the center of the dash, behind and to the left of the radio. Good luck if you ever have to take it out.

 

Since this took me a while to find I hope it helps someone.

If you run across a code 10 Sensor resistance low. (possible short) Disconnect the sensor on the pig on the rear axle and recheck. If it still shows a code 10 sensor is probably ok... If it switches to a code 9 (sensor high resistance) probably bad sensor.

If you still show a code 10, pop the hood and look in the mess of a wiring harness above the drivers wheel. It took me a while to find. There is a 8 pin, gray, rectangular connector. Look at the wires on it. The twisted pair of red and green are the sensor wires. It looks like the insulation is poor and it shrinks and shorts out. I think being twisted it does not help either.

I took oil free carb cleaner and washer off connectors the best I could and blew them dry with a compressor, Seperated them well and hit them with a few layers of liquid tape. Electric tape was not going to work that close to the connector. It looks like it is a common problem.

Here is a pic of both ends of the connectors.

 

The 1987 does have rear anti lock breaks because I have one and it is equipped on them