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Cadillac Repair/1990 Cadillac Seville


I have a 1990 Cadillac Seville and the error code says: b121 Twilight Sentinel circuit problem
how would you fix that what part is it thats messed up also I'm trying to find the power steering pressure switch and I can't seem to find it can anyone tell me where that would be located fyi...not a mechanic not even close


You really do not need to be a technician (or close to) to diagnose and repair the problems in your car. In fact, from my decades of dealing with dealer technicians, many of them don't have a clue either and replace parts trying to fix a problem without ever fixing it, lasting as long as the customer has money. Of course people go to dealers because they represent the manufacturer, so the thought is they must know what they are doing. Want to bet?
OK, to your issues--there are too many possibilities without me being at the vehicle. I could give you any old answer which may or may not be correct, but I am concerned about my loyal readers and their pocket book.
The manual comes with easy to follow diagnostic flow charts that in many cases do no require any specialty tool other than a cheap multi-meter available at any local parts or radio store such as Radio Shack. The service manual is the bible to your specific car and one does not need to be an auto tech to understand it. In fact, someone with your limited experience in vehicles could get a feeling of accomplishment repairing most every problem that turns up.

The service manual is one of the most valuable tools in the auto technicians arsenal, but many are too lazy to read and parts changing is the way they go. With you doing your own minor repairs, no longer are you at the mercy of a "mechanic."

Good luck and let me know how it turns out.

Auto theft claim under investigation? Have an examination Under Oath coming up? Auto theft claim denied? Before making the mistake and turning to a general attorney that does not have over 2 decades of experience in this area, give us a call at 1-866-490-1673 or 1-903-513-7808 (cell) or contact me at or visit our site for information you are not told in those cute insurance TV ads. For the last 20 years, we are the only firm that represents insured's in the US and Canada and serve as expert witnesses and consultants to attorneys in this area.

The first thing is to acquire a 1990 Cadillac Sevile factory service manual. You can find them for sale on Ebay and Craigs list.

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Rob Painter


Alarm system questions cannot be answered on this forum. These systems are not what I can answer. Without being physically at the vehicle and not knowing what kind of electrical service has been done on the vehicle, there is no possible way to give an accurate answer over the internet. My expertise is in Ignition/key based anti-theft systems. These issues include GM VATS (resistor chip in key blade) PASSLOCK (MRD)-ignition lock rotation based, no special ignition key and the PKIII Transponder (computer chip in key) systems. These systems are not alarm based and are integral with the starting of the engine. This is why I cannot diagnose alarm problems without physically looking at the vehicle: Alarm systems are a completely different annimal than ignition key/lock based anti-theft system. Many alarm questions come from vehicles 10 years old, and since older, many hands that had been involved over the years.I am an expert in all GM factory (ignition/key based)systems. Alarm system questions pose to many situations beyond my knowledge as to what has been done to the vehicle over the years. Some guy may have actually wired the stereo into the alarm system. Who knows? Over my past 30 years in vehicle wiring repair, I have seen unbelievable wiring disaters done by guys that consider themselves "mechanics." I have seen stereos and alarms intalled using surgical tape. I have seen modules burn up, un-fused circuits, wiring jambed between the doors and even lamp cord used for a starter kill. To answer alarm questions over the internet without examining the vehicle is like asking; What does it take to remove a dent?


Education/Credentials-ASE certified. 11 years with a GM dealer and 17 years with a repair facility dealing with only the repair of theft recovered vehicles.

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