Reverse light adjustment for 1988 chevy silverado

Faulty switch maybe. Check it works.

Right here 1988 90 Chevrolet Pickup Alarm Remote Starter Keyless Entry Wiring

Are all parking lights on or just front daytime running lights only? Either case sounds like a light control module in your fuse panel stuck.

sounds like your cluster has a short

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Did you check the park fuses, note the diagram, rr and lr. Use a test light to check voltage at fuse circuit, headlamp switch on. That should tell us if problem is before the fuse or after.
You always want to check voltage and ground circuits, for lamps. Do the front park lamps work?

take it to a dealer, it is most likely under warranty. tell them to check the neutral safety switch adjustment. it also generally is the switch for reverse lights.

I would take the bulbs out and put the trans in reverse, the check for voltage with a test light or multimeter. If no voltage is present then it's more likely a problem with the reverse switch which is located on the trans.

bad switch or out of ajustment

I had the same problem. My backup lights wouldn't come on in when I put the auto. trans. shifter into the Reverse position. They WOULD come on briefly as I moved the shifter from Park position into Reverse, but would go off again when the shifter reached the Reverse detent. I got the solution from the Haynes service manual, in which the relevant switch is referred to as something like the neutral safety switch. Check on top of the steering column close to the firewall. Set the parking brake, then move the auto. trans. shifter into Neutral position. Get under the dash and rotate the neutral safety switch clockwise as far as it will go. Then move the shifter into the Park position, and your switch should be set. If the backup lights don't come on now when the shifter is put into Reverse position with the ignition switch 'on', there may be another problem.

You must have a bare wire at the back of your truck that's shorting out where gravel stones have pounded the outside coating off. If you have an after market trailer plug on there, you might want to check that out too. The connections to your main wires from the trailer plug, are never done properly, and always cause problems somewhere.