Where is the fuel injector fuse located on a 1990 Buick lesabre?

Try 1990 buick lesabre fuse diagram Google Search

Jim, Remove passenger side kick panel to access the fuse box where horn fuse is located #3 fuse in your manual, box fairly high up under dash. Horn relay under hood/engine compartment fire wall.
Check the attached links,instruction and guides and a manual for your buick, Good luck
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http://pdfstream.manualsonline.com/8/81776d98-998a-493c-aac6-a5895c51d47b.pdf
Horn doesnt work Ricks Free Auto Repair Advice

You will need a fuel injector testor, about a $100, and a fuel pressure guage, about a $100, to flow test the injectors.

You can ohm check them with an ohm meter to see if one or more has shorted windings. Remove the electrical connector and test between the two pins. They should all be about the same ohms. If one is significantly lower than it is probably bad. Its best to check them when they are hot (after the engine has warmed up).

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The fuse compartment is located on the left side of the dashboard accessed by opening the drivers door and removing the cover.

The sensor is a screen-looking device...located at the input to the fuel injection port. Follow the large air hose from the air filter...it should be easy to see once that end of the hose is disconnected.
Try cleaning it before replacing it...I use carb cleaner (generous spray of it directly on the screen). Then reset the Check Engine light (AutoZone can read and reset for you free).

For 1990 Buick Lesabre 3.8L FI OHV 6cyl the Control Module-Ignition is located: Under hood, passenger side, front engine area, mounted on upper passenger side of cylinder head under ignition coil.

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I believe it is located on the left end of the dash. You will have to open the driver's door to access it.

no. What is wrong with it. I can help you.

even if you have preasure in the line that does not mean you have fuel going into the engine. you should check the injectors to see if they are spraying and if not you need to check the injector pulse to find out if the PCM is sending the signal to them to spray. to check injector pulse you will need a noide light to test the pulse it the light lights up you have pulse, but easy way to check is pull an injector and turn the engine over see if it sprays.

If fuses are good, I would check the flasher. Located under driverside dash by the steering column.