gauge readings erratic

I have a 91 Dodge W250 with the Cummins diesel engine. Recently I experienced some air in my brake lines and when I pressed the pedal to the floor my emergency brake and anti-lock brake light on my dash lit
up. I bled the brakes but the lights on my dash stayed lit (except now they go out when I press the brake in?). I also began experiencing intermittent static on my radio and my speedometer is fluctuating wildly. I have recently noticed that my oil pressue gauge and temperature gauge also appear to be reading erratically. I have checked all the fuses but nothing was blown. I also have not experienced any engine problems. Does anyone have any ideas what might have caused this? It does seem to have originated when my brake pedal was depressed all the way. Could this have broken something?
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The brake computer is behind the glove box. Open the door and the glove box will come out. Unplug the computer for a few minutes and plug it back in. This will reset it. If the lights stay on you need to look for the problem. Get a service manual at the library and follow the test procedure.
Al
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Relating it to my 89 CTD, 3 things come to mind. 1. Brake proportioning valve stuck or malfuntioning.( mith need to bleed some more. 2. CVR(constant voltage regulator dying). 3. A short. I had one where the insulation rubbed through on the fuel cut out solenoid. JMTCW
On 12 Oct 2005 15:16:59 -0700, snipped-for-privacy@gmail.com wrote:

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You have to go into the dianostic mode for the ABS. The light will brake light will flash and then you look up the problem with a repair manual, Speedo can be acting up from a dirty sending unit on the trans. or MOST LIKELY a worn or shorting wire. Like Big Al suggested reset the ABS computer by unplugging.
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Well I haven't had any luck. I tried resetting the brake control module and checked all the fuses. I haven't took the gauges cover off to look for any shorted wires yet, but that is next. I still believe this is some kind of systematic problem and not related to any one bad sending unit. When the problem first started the speedometer would work fine if the "brake + anti-lock" light was NOT on. When "brake + antilock" light was on the speedometer would start jumping around. Like I said in my original post this all started with air in my brake lines. I'm wondering if the brake control module might be bad and somehow causing all these other problems. Anybody have any additional thoughts on this weird behaviour?
chuckster wrote:

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If the speedometer is jumping around as you say, the most likely cause is the rear wheel speed sensor located on top of the rear axle. This problem has been seen in here over and over again and replacing this sensor almost always corrects the problem with both the speedometer and the ABS light.
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'91 truck.... no RWSS
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I hit 'send' too quick... no RWSS that has anything to do with the speedometer. IF he has ABS, there's a rear wheel sensor - but the speedo comes from a sending unit on the transfer case (doubt they were still using mechanical speedometers in '91, but I'm not positive)
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I didn't see anywhere where he gave the year but if it is a 91... I didn't know that they were even offering anti-lock brakes in 1991.
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First post of the thread.... he stated it was a '91 Dodge W250
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I believe you, I just never saw the OP, just the one I responded to.
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Rear wheel only, and the speedometer is electronic. Sensor is where the speedometer cable would normally attach.
Al
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I have tried all the things listed here and still have not solved the problem. Things done so far: 1) changed differential speed sensor 2) checked for shorts 3) checked for error code from the ABS control module 4) changed voltage regualtor 5) bled the brakes (again) 6) replaced battery 7) checked alternator output at battery
I would like to add some new info I have noticed. The static from the radio disappears and all the gauges read fine while vehicle is sitting still just idling or if I'm stopped with the brake and clutch depressed. I have noticed that the lights dim intermittently now as well, especially if it is cold weather. I checked the alternator output and it appears to be charging the battery however I do wonder if perhaps the alternator is somehow causing this. There are 2 posts on my alternator that have wires running to the voltage regulator. One of these posts while running produces 14.8 volts, the other wildly flucuates. Is this normal?
Thanks, Brent McConnell
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