I have no reverse in every gear I shift to it go forward motion except for park

I have a 2001 Xterra and was having a little transmissions problem it would not shift to 4 over drive so I did some research and figure it was the shift solenoid was bad and tested and replace it with another from an infinity truck with same motor I think. So I decided to change the filter and fluid also when I removed the valve body I removed all the bolts holding it together to get to the shift solenoid when I exchange for a new one I did a voltage jump to see it click and did not hear anything so I figure it might be bad but I went on and replace it because it can’t be worse then what it was I’ll just do it replace it with a good one later. When I put back everything together again an fill the fluid ,started up the truck the check engine was gone but I had no reverse and every gear I shift to it in drive or the low gear even neutral it in forward gear did I put it back wrongly or miss something I drove it a little around the block then just park it I’m curious if I plug in the wrong wire to the solenoids please help

It may be that the replacement solenoid is shorted out and messing with something else inside the transmission, a sensor or another solenoid. Try putting the old solenoid back in. Or just install a known good solenoid. The way an automatic transmission works is by very high pressure circuits in the transmission fluid, so if there’s any internal leaks now b/c of misplaced gaskets that could be the problem too. In any event it looks like you will be removing the valve body again. Did you replace all the gaskets involved with new ones the first time you did this?

I put back on the old solenoid but did not replace the valve body gasket because of I thought it still look like it in good condition after doing all that it has kinda whining noise for lack of funds and was in rush to get it done so I can drive for work. I’ll replace every gasket and o-rings when I put in the new solenoid this time. An could low fluid cause it to do it too.

Good idea. And yes, low fluid is almost always the first suspect w/transmission problems. Often just topping off the fluid level fixes the symptom and is the thing to try first if the fluid is low.