What supplies the ground for the starter enable relay control( which is the pass-key II decoder module on a 1996 pontiac bonneville? I can not get the starter to engage unless I probe on side of the starter enable relay with a test light while turning the ignition key. It will engage the starter then, but if I take the test light off of the relay and then turn the ignition key it will not engage the starter. I an looking for what controls or supplies the curcuit for the key with the diode imbeded in it.

Question edited for clarity.
Question moved to model category.

It is in the engine compartment Fuse and Relay Center. However, it may not be that but good place to start.

https://www.google.com/search?q=1996+cadillac+deville+starter+relay+location

Test, don't just blindly replace components.

https://www.google.com/search?q=1996+Cadillac+Deville+no+crank+no+start

Best idea by far. A pro grade scan tool computer can diagnose in 20 minutes

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Your look at owners manual or a wiring diagram .

http://www.bbbind.com/tsb-wiring-diagrams-database-results/?type=WD&years=1998&make=50&makeDesc=Pontiac&model=538&modelDesc=Bonneville&system=5&systemDesc=Engine&subsystem=99&subsystemDesc=Charging%20System&docid=7507782

Looking at the wiring diagram i wouldn't suspect a bad fuse , main battery cable to the s terminal on the starter solenoid , starter relay , PNP - park neutral position switch , PASS KEY II theft deterrent module or the ignition switch . Do you know how to use a DVOM - digital volt ohmmeter to test electrical circuit's ?

Could be park neutral safety switch , move gear selector to neutral too see if it starts then .If not that , you need to view wiring diagrams an test the starter electrical circuit's . Also should read how that circuit works , what's all involved . Does the security light come on when it won't start ? Starter enable relay , pass - key decoder module . alot involved here . Free wiring diagrams here http://www.bbbind.com/free-tsb Enter vehicle info. Year , make , model an engine size . Under system click on engine then under subsystem click on charging system . Starter circuit is located there also . Do you have knowledge of anti- theft system on GM vehicles of that year ? How to videos on youtube for testing starter circuits .

It's the anti-theft system . (SECURITY ) Keeps vehicle from being stolen !
Important: If the wrong ignition key is used in an attempt to start the vehicle, a Data Trouble Code (DTC) will be set and the Body Control Module (BCM) will not send a fuel enable or starter enable message to the Powertrain Control Module (PCM) for three minutes even if the correct ignition is used.
The Pass-Key II?® Theft Deterrent system prevents vehicle theft by disabling the starter motor and fuel system. If the Body Control Module (BCM) dose not identify the use of the correct ignition key to start the vehicle, the (BCM) will communicate a message to the Powertrain Control Module (PCM) which will disable the crank relay and fuel delivery to the engine.
When the (BCM) identifies the use of the correct ignition key (resistor pellet) to start the vehicle, the (BCM) will send a fuel enable and starter enable message to the (PCM) which will allow the vehicle to start.
Your best bet would be have it towed to a qualified repair shop !

There is no wire you can cut ,doing this will make your vehicle never start .
The Personal Automotive Security System (PASS-Key II?®) is standard equipment on the vehicle. The system is designed to prevent vehicle theft by disabling the engine unless an ignition key with a specific electrical resistance is used in the ignition cylinder. The PASS-Key II?® system and the universal theft deterrent operate separately. The universal theft deterrent system is optional. The PASS-Key II?® system includes the following components:
?€¢
The ignition key

?€¢
The ignition cylinder

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The body control module (BCM)

?€¢
The starter relay

?€¢
The powertrain control module (PCM)

The ecm fuse also powers the pass-key module on the key barrel.
See diagrams below. I recommend you probe the starter enable relay socket to see if it is getting the ground signal from the pass-key decoder whole someone tries to start the car.

Does the SECURITY light on the instrument cluster flash or is it on steady ? The problem with this system is the contacts inside the key lock cylinder wear causing this problem ! It's not the module more then likely ! This system you can do a by-pass on ! Measure the resistance of the pellet on the key , go to radio shack buy resistors to = the key pellet resistance . Find the wires from the ignition lock cylinder under the dash , disconnect the connector from the dash wiring harness an solder the resistors into the dash wiring , not to the lock cylinder . There are videos on youtube showing how to do this by-pass .
When a key is inserted in the ignition, contacts that are located in the steering column (ignition) lock cylinder contact a resistor pellet located in the ignition key. The theft deterrent module measures the resistance of the key pellet. The module compares this value to a value stored in memory. The theft deterrent module then performs one of the following functions:
• If the values match, the theft deterrent module performs the following system enable functions:
• The module provides a ground for the theft deterrent relay at terminal A4 (CKT 625, YEL/BLK). The ground enables the starter to operate.
• The module sends a proper pulse width modulated (PWM) signal to the PCM. The signal travels via CKT 229 (DK BLU), terminal A3. When the PCM receives this input, it enables the fuel delivery system.
• If the values do not match, the theft deterrent module performs the following system disable functions for approximately three minutes:
• No ground is provided to the theft deterrent relay. The starter is disabled.
• No command is given to the PCM in order to enable the fuel delivery system.

GM VATS Key Resistor Key Security Bypass

Have it checked for DTC'S - diagnostic trouble code's . I suspect the problem is with the tdm module or the ignition switch ???? Assuming will only get you into trouble . If the PCM - engine computer does not see the right coded meassage from the TDM it won't turn on the fuel injectors or it will cut them off in two seconds . .
Buick Security Systems 1998 Chevy is the same .
Ignition Key With Wrong Resistor Pellet Code is Used To Start Engine
The theft deterrent module performs one of the two following actions when you attempt to start the vehicle with a wrong ignition key:
• There are 15 PASS-Key® II resistance ranges. The PASS-Key® II resistance may be one of the 14 valid but incorrect PASS-Key® II resistance ranges. The theft deterrent module will perform the following actions when you attempt to start the vehicle (if the condition is present during an engine start attempt or for 1 second any time after the engine has started):
• Turns on the SECURITY indicator
• Sends a password to the PCM through the fuel enable signal circuit
• The password disables fuel delivery to the engine.
• Disables the theft deterrent relay, which disables the starter circuit
• Disables sampling of the PASS-Key® II resistance for 3 minutes
• The 3 minute time period is called the shut-down period.
• Disconnecting the battery will not clear the timer sequence. The timer sequence will resume when battery power is restored.
• Inserting the proper key during the vehicle shut-down period will not start the engine. The engine will not start until the shut-down period has elapsed.
• After the shut-down period, the engine will start if the correct ignition key resistor pellet is used.
• The PASS-Key® II resistance may be correct and allow the engine to start. Later during the same ignition cycle, the PASS-Key® II resistance may be one of the 14 valid but incorrect resistance ranges. The theft deterrent module will perform the following actions:
• Enters the fail-enable mode
• Turns ON the SECURITY indicator
• Sends a password to the PCM through the fuel enable signal circuit when more attempts to start the engine occur
• The password allows the fuel enable circuit to deliver fuel to the engine.
• Enables the theft deterrent relay, which also enables the starter circuit.

Ignition Key With Correct Resistor Pellet Code is Used To Start Engine
The theft deterrent module performs the following actions when the correct ignition key is used in order to start the vehicle:
• Enables the theft deterrent relay. The theft deterrent relay enables the starter unit.
• Sends a password to the Powertrain Control Module (PCM) through the fuel enable signal circuit. As a result, the PCM allows fuel delivery to the engine.


By pass theft system .
GM VATS Key Resistor Key Security Bypass

your vehicle is equipped with Personal Automotive Security System (PASS-Key II(R)).
This security system is designed to prevent vehicle theft by disabling fuel system and starter unless an ignition key with a specific electrical resistance is used in the ignition key lock cylinder. PASS-Key II(R) system operates using sensing contacts, which are located in the ignition key lock cylinder. These contact a resistor pellet located in the ignition key. When lock is rotated, battery voltage is applied through appropriate fuse and resistor pellet to theft deterrent module (except Century), or body control module (Century). Pellet resistance is then compared with programmed value in the theft deterrent module or Body Control Module (BCM).
System components include ignition key, ignition key lock cylinder, theft deterrent module (except Century) or BCM (Century), theft deterrent relay and Powertrain Control Module (PCM). The PASS-Key II(R) system can also be supplied as a special equipment option on some vehicles

It will reset itself after about 10 minutes. You just have to wait until you hear a click and the pass key light goes off.
Be sure to clean the little metal strip on your key while you're waiting...

check the ground bar under the carpet by the drivers door sill it is probably corroded