My ABS light is on and there is a sound coming from the abs Metal box in the bonet and the speedometer is not working. The mechanic diagnose it as rear sensor(is it the rear ABS speed sensor. and would it affect the auto transmission. my car is nissan silvia S15 model 1999-2002 . i'm also finding it difficult to find the spare parts ....any suggestion. thank you

Question edited for clarity and make some real sentences.
Question moved to model category.

See the first video, but by the sounds of it, you need an auto electrician with a pro grade scan tool computer to diagnose these faults electronically. ABS, Speedometer and Transmission Solenoids.

https://www.google.com/search?q=1999+Ford+F-250+4x4.+The+ABS+light+is+on%2C+and+the+speedometer+doesn%27t+work

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but is the odometer working right.?
if is, the speedo is bad.,inside cluster. IP.
if is wrong too ,so is send data to it is wrong. speed data
some cars have bcm that sends speed data to cluster.
in the USA we scan the PCM and it tells use clearly why it fail.
even communication bus error. (to cluster)

Speedometer Not Working ' Range Rovers Forum
I would first check all fuses you may have several fuses which can be associate with your problems, not sure why radio would be associated.
My 07 Silverado gave me ABS, Traction control light it turned out to be rear axle left and right speed sensors which are used for ABS, all four tires have a speed sensor for ABS on my Silverado. My speedometer sensor is on the transmission. Just pointing out need to have the code read. My code reader did not read ABS codes, you need a code reader which reads ABS I had to go buy one. It told me the sensors which needed to be replaced. Want to add it could be a wiring issue to the sensors also.
Range Rover Sport L320 ABS Warning Light How To Diagnose - YouTube
Speedometer Not Working ' Range Rovers Forum
I would also suggest you get the code read auto parts store where I live will usually give you the code. You can search on google, put the year, make, modal and the codes which was read, you will get some posts/links which can tell you what the problem is and what others did to repair it.

Sounds as if it is a cable or the speedo sensor. If there is ABS it could also be the ABS sensor playing up on one of the wheels.
Best advice is take it to a diagnostic place or find a local mobile diagnostic mechanic where they can tell you why the light is coming on the desk.. This may be a cheaper way as they may be able to tell you the exact part which is showing the fault.

Need to have a shop check for codes & diagnose the issue
Somewhere between the speed sensor & abs sensors you have a problem

You will need to have your car's ECM (Computer) read by a OBD II scanner to determine what Trouble Code your ECM is giving so a mechanic can properly diagnose the problem. You can go to your local AutoZone store and they can pull the codes out of your ECM for no charge.

The ABS module when active makes noise when it is trying to control the vehicle by applying "leave" and "press" mechanism. If the lights are coming on , it is possible that the ABS needs to be fixed. Take it to the authorized service centre to electornically diagnose and reset the codes.

Sounds like a bad ABS control module is at least part of your problem. The symptoms are usually and ABS and TRACS light intermittent or constand and eventually your speedometer works intermittently or totally quits. This guy rebuilds/upgrades them for about $140. New ones run over $800. http://home.earthlink.net/~vicrocha/Volvo_Parts/Volvo_ABS_removal.htm

Sounds like your getting abs activation when its not needed. Most likley one of the wheel speed sensors has failed. You do need to have a scan tool to read the live data from the abs module as the problem is occurring to pinpoint which sensor is faulty. The abs light will not come on because the abs module thinks its just working normally. I'm an ASE certified mechanic and have seen this problem many times on various vehicles. You might have to pay somebody to diagnose it, but replacing the sensor it a very easy task. I hope this helps.

The Airbag and ABS are separate systems and un-related, the speedo is related to the ABS light, I think if you run a self test on the system computer there will be a trouble code for the transmission speed sensor, the output of this sensor is used by the ABS and the speedometer. The airbag is most likely a defective rotating contact under the steering wheel, we techs call it a clock-spring contact because of it's shape, it allows the connection from the steering column to the airbag. CAUTION! If you want to change out this contact the steering wheel needs to be pulled, follow factory recommendations on dis-arming the airbag, it can be very dangerous if you don't.