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Intermittent ABS/Brake Light On -1st Gen


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Good Morning fellow bombers!

Hope this fine day is being good to you all.

 

Believe it or not I have a new issue with my old ‘93.

My ABS/Brake light on the dash will come on intermittently.  I can find no rhyme or reason, no pattern.  It just feels like coming on.

I know somebody on here must have dealt with this at some point before.

I did a search but found nothing.  
I don’t even know where to start looking for a problem on this so I’m turning to you knowledgeable and helpful folks.

 

Thank you and I hope you all have a stellar day!

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Speedo is picked up from transfer case. The only sensor on the truck for abs is on top of rear diff. Betting it's missing signal due to metal shavings or possibly bad sensor. 

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Posted (edited)

Well the sensor is original but I just had the diff fluid changed a few weeks ago.

I’ll just go buy a new sensor and change it out.

should be fairly straight forward…even for me!

Edited by Ternkiem
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  • 4 weeks later...
Posted (edited)

Finally got around to changing the ABS sensor in the differential.
Made no difference…still just comes on if it feels like it.  Sometimes it will even go out if it feels like it!

I thought maybe a speed sensor on the tranny so I bought one of those.  Can’t find that on the tranny anywhere…

Could that sensor be the problem and Where is it located?

 

I did find the 3-Wire Neutral/Safety Switch was barely making contact though.

I cleaned the contacts and plugged it all the way in this time.  
I know that wasn’t at fault because the damned ABS/Parking Brake light came right back on again.

 

I’m starting to get pretty frustrated with it now and since it doesn’t effect the driveability I may just ignore it until I get back from my cross-country trip (leaving next Wednesday) with it.  Problem is I’ll be towing 10k pounds and I’d like to know everything is working properly.

My mechanic will adjust the brakes for me tomorrow…Maybe that will have an effect on it, who knows. 🤷🏻‍♂️

Edited by Ternkiem
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13 hours ago, Big Russ said:

Brake Switch on the pedal - My 2nd gen did this too.


ive replaced that 3 times over the years, but it has been a long, long time since the last one.

What the hell…they’re cheap, may as well replace it again.

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Found and replaced the output shaft speed sensor today.  Nothing changed.

started tracing wires…got lost under the dashboard.

Anyone have a wiring diagram handy?  marksmith maybe??


 

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I do not have wiring roites/diagrams for that truck. 

 

If it were here I'd component test the sensor then trace the wires (power probe has a wire tracer tool for this)

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Looks like big Russ as correct (so far). I replaced the breaker light switch and the abs/parking light stopped coming on.

yea!

  • Like 2
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Posted (edited)

Well…both lites came back on after a very short time.  I’ve just been too busy to give this update (had to pull a 11k pound load to Springfield, MO for my daughter.

 

there’s only a couple of things left to try (that I know of anyway).

1.  Change the neutral-safety switch

2.  Change the E/brake switch

3.  Unplug the black box behind my glove box.  The ABS light will go out but not the E/brake light. There’s an awful lot of wires on that plug and I don’t know what other systems will be affected.  Any of you know?


I have time to do any or all of these things while I’m stuck in Springfield, MO to get my A/C fixed.

Edited by Ternkiem
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  • 4 months later...

Just wanted to update this thread…

 

After a boatload of troubleshooting and investigation it appears I may have fixed the problem (at least temporarily).

During my research into this issue I came across an OLD, OLD thread on another forum.

One of the responders said to disconnect the E-broke switch, the Low Pressure Vacuum Switch (which is located directly beneath the hood spring on the drivers side), and the Distribution Valve connector.  Then, if the light does not go out you know your problem is with the ABS system (either the dump valve or the sensor). If it goes out then reconnect each item one at a time to see which one will cause the light.

So…I did this and my light DID go out so now I needed to find out what the cause was.  Before I started reconnecting them I cleaned all the connectors (both sides of each) then reconnected the E-brake switch and started the truck.  No light…so I turned the truck off and reconnected the Low Pressure Vacuum Switch.  No light again…so following the same procedure I reconnected the Distribution Valve and started her back up.  NO LIGHTS!!  YAY!!  
Took her out for a 25 mile stop and go test drive through town and around the island with no lights coming back on.

Now I don’t know what the actual cause was or which connector was the issue but I swear all I did was clean them and put them back on.


In the end it works as it should (at least for now).  I’m keeping my fingers crossed it stays that way for a long, long time.

 

HAPPY THANKSGIVING ALL!!

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