How do i chage the starter on 1996 caddy seville

Ohh... The notorious caddy starter. Lol
It's under the intake manifold. I've done a few. Unbolt throttle body from intake. The throttle body kinda loose where it is. Remove intake manifold. You can't miss it once intake is removed

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If it's like my 1989 Caddy Seville - it's under the distributer cap.

is the check engine light lit?

Ask a caddy dealer parts guy to tell you what type of suspension you have.

www.strutmasters.com sells conversion kits but you have a 500 dollar car there and how much are you going to spend on it. it will still be worth 500 dollars after you replace the entire suspension.

the starter is under the intake manifold

Have your alternator tested too; if it has a sick diode, it can drain the battery and also shunt current away from the starter as well as damage the battery by applying unrectified voltage on one leg of the output. I replaced SIX (6) Delco alternators in nine years on a car built in '95. It would have been more except the engine failed at 57,600 miles and I junked the lemon.
If the starter solenoid is not integrated on your Caddy, it too can fail which will cause too much lost voltage trying to get to the starter. 

You should check out www.reliable-store.com they have info on repair, service, wiring diagram, electrical diagram, fuse diagram, torque specs, troubleshooting,
PCV, gear box, owner's/service/repair/parts manual, fault codes, error codes, etc everything on all vehicles. must check it out

In The Fuse Box Usually But My Bets On The Starter. Hit The Starter With A Hammer And See If It Starts Then. It Should And Thats Your Starter.

http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c15280090328

it is the modulator valve..replace it.