So I've been trying to install Twilight Sentinel into my '75 98 for the past couple of days and I've been struggling with getting it to work consistently. For reference, the 98 wasn't offered with the option from the factory, though dealers offered it as an option after the fact. I've sourced a headlight switch sub-harness, amplifier / controller, photocell, headlight switch with the extra terminals and rheostat "stack" (it has the rheostat for Sentinel as well as another for the separate auto-dimming high beam option) from a '77 Eldorado. I've connected the existing wiring from the old switch back up to the new switch, supplied 12v from one of the "ignition" terminals on the fuse panel to the power connector for the controller and while everything works as it did before, I'm having issues getting Twilight Sentinel to work consistently and I think it may grounding.

For reference on the original harness the controller's ground apparently went into terminal 12 on the headlight switch (courtesy light ground) and the rheostat grounded out through the metal chassis it was originally mounted to. I've since tried connecting the ground for one, the other and both to different locations (the IP harness ground under the dash, the ground on the headlight switch, etc.) and I've had mixed results with each. Either the lights don't come on when moving the key forward two positions (controller grounded, rheostat not grounded), they come on but don't turn off with the delay (rheostat grounded, controller not grounded), the lights come on but either immediately power off with no delay when switching the vehicle to off or relay in the controller trips on and off continuously (both grounded to the same point). There has to be some specific method for grounding both the controller and switch, but as of yet I've been unable to figure it out. If anyone could offer assistance with this it would be greatly appreciated.

 

Don't ground either the controller or the rheostat to the chassis. Grounding of metal surfaces (i.e. the chassis) that aren't intended to carry current is a multi-point ground. These should be kept seperate from a single-point ground, or the manufacturer's intended ground for an electronic component.

I'd run them both to the ground point on your fuse panel. If that doesn't work you may have to manufacture a cable run specifically to your negative battery terminal.

BTW, do you know this Twilight Sentinel equipment works (did you get it functioning from another car)?

 

I know it works now.

The rheostat needs constant ground for the circuit to close and enable the whole system.

The controller needs to be grounded out through the courtesy light ground (the white wire on the headlight switch) as the ground for the controller is used only to trigger the timer for the delayed off. With it connected to the courtesy light ground, that means the timer starts when the key is in the off position and a door is opened (and the lights on buzzer only sounds when the lights are manually on, the key not in run and a door open). If you attach the controller to constant ground like I did it will start the off timer immediatley after headlights come on and immediately power them off when the door is opened.

Additionally, the relay in the controller had a broken solder point where it was attatched to the board, causing intermittent operation of the unit.

With it groynded properly everything works as you woukd expect. Now I just have to figure out how to mount the new switch...