I have a 2007 Suzuki Reno hatchback. my My car does not gointo DRIVE , PARK or REVERSE without slamming into gear. and when this happens the car stays in low gear and only has half the power. also I have to diconnect by battery just to get my keys out of the ingnission because when the car is in park we have to use a key in a slot by the gearshift to get it out of park. we are told that it is a external sensor problem are these easy to change

wow ,no engine or country stated, not that is Challenge.
RTM yet, this is advanced repair,,, skipping steps, you will fail.

the line up, got one of these?
1.4 L E-TEC I4 (petrol)
1.6 L E-TEC I4 (petrol)
1.8 L Family II I4 (petrol)
2.0 L Family II I4 (petrol)
2.0 L RA 420 I4 (diesel)

if in usa
this covers you
https://suzukipitstopplus.com/Products/1068-2007-forenza-reno-service-manual.aspx

if not, not.,

the cluster lamp, well that's easy,
turn key, all lights i dash glow as a test. see it TPMS
or open up glove box operators guide, see that page telling you same? and more.. on topic, lost it get one?

4 bucks a gander
https://suzukipitstopplus.com/Products/1067-2007-reno-owners-manual.aspx

same for FSM book (service), see it? see both?

Do you mean the little poorly engineered sensor that tells the trans what gear your car is in that failed on our car twice before we dumped it and brought a New Camry ;-), yea that is located on top the Transmission housing. It's 3 bolts to remove, check the Suzuki forum for the write up of how to replace it. When it fails the car will go into limp mode, hopefully not on the highway, but its easily enough to replace in your driveway with the E brake engaged and a few common wrenches. it may need to be adjusted, but even that has a limited range, the only way to avoid its premature failure is to make sure every single time the car must be at a complete stop and when you feel the car engage the next gear ie Drive to Reverse, only then you can apply the accelerator. Anything too soon and you'll strip that sensor every time.

take out the head light

run the fault codes to find the fault in the transmission

Suzuki recommends 10w30 grade oil and it will need about 2.4 quarts of oil without a filter change and 2.6 with a filter change.

need to replace brake light switch or at least test

your brake light switch above the pedal has failed or is stuck in. Look up at it to see if it is releasing the button when the brake is pressed. If yes, replace the switch. It only costs about $20, but may be a pain to get in and out. The switch looks like this:

You may have to add a little silicone to the gaskets, especially around the crankshaft area. be sure to tighten the bolts down firmly.

when check engine light comes on i lose 75% of my hourse power and it slams into park, reverse and drive