I have my blazer 1999 4,3 automatic 5 doors just one week and I found some problems with it. I can't find exact answer where is backup reverse lights switch? When I put on R theres no light... And bulbs seems to be ok and fuses too. What else to check? My mechanic thinks it could be something with neutral position switch as I found is this proper name for it. Or is there any separate sensor which activates the lights?

 

Have you tried to testing the voltage where the bulb plugs in? And are all of your fuses good? Sometimes if one fuse pops that doesn't directly control one thing it can still stop that thing from working.

 

I will check fuses one more time today. Which one I should check first?
And is there some separate switch on auto gearbox which energizes backup lights? Or that lights are controlled from neutral position switch potentiometer I think...?

 

They should be controlled by the neutral safety switch on the transmission so if you don't see any bad fuses then I would replace that. From what I've read its as easy as unplugging the switch, unscrewing it from the tranny and then screwing the new one in and plugging it in.

 

Problem solved :-) I checked fuses and all was ok but today I saw there's one missing... Exactly for backup lights 25A.. I put new one and all works great :-) second fuse was fine like previously. I didn't know there's two separate fuses for backup lights.
I also replaced Neutral Position Switch for new one.. Old one was damaged and someone fix it no one knows how long ago and it has missed one track inside and plugs was really in bad shape.