92 Buick roadmaster wants to cut off when I get ready to stop at lights after the service engine light comes on what could it be

did you check bulbs , check for fuse , check sensor on tranny,
is shift selector moving correctly,

A cheap cooling sensor might not start the fan. Make sure the one you or your mechanic bought is a quality product.

Jump pins A and B on the ALDL (data link connector). Turn the key on and the check engine light will flash the trouble codes.

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take a test light and make sure you have power to the injectors. then put the test light to the positive side of the battery and check for injector pulse from the ECM by trying to start the vehicle and see if the light flashes.

If you stop by auto zone and find out what codes are in the computer we can go from there. Did you check fuel pressure?

With GM when the tail lights and dash lights go out together it's time for a new headlight switch. Hope this helps.

If you check your owners manual or purchase a repair manual it should tell you.

need new distridutor, same problem i had replaced two so far, 94 buick LT 1

try a tune up-plugs and wires-and air filter

Check your fuses first. In a '92 Roadmaster, they would be number 14 and 15, light blue 15A fuses. I am not sure about other years, but your owners manual should tell you. Otherwise it could be the headlight switch, or the Twilight Sentinel Module if your car has the option.
I had a similar problem a few months ago with my '92 Roadmaster Wagon. My problem was due to the Twilight Sentinel Module. If your parking lights do not come on (dash lights, too), but the headlights do when your Twilight Sentinel should turn them all on, try to use the rocker switch to turn on the lights. If the parking lights come on with the rocker switch, I believe you need a Twilight Sentinel Module. However, if you do not have a Twilight Sentinel Module, or your lights do not come on using the rocker switch, you may have a bad switch or faulty wiring. The Twilight Sentinel Module is located way up under the dash, to the right (passenger) side of the steering column where the column goes through the firewall. It looks like the one in the picture, and could be off white or gray, or perhaps a different color.