When should the middle rear light be lit?

[JaguarS4R]

Sometimes when I have the headlights on, the middle rear taillight is lit and sometimes its not. Should it only be lit when the brakes are applied or all the time?

[DaKat]

W/brakes

[JaguarS4R]

W/brakes

so when the headlights are ON, the middle lights should be off unless I hit the brakes?

[UDL]

Sometimes when I have the headlights on, the middle rear taillight is lit and sometimes its not. Should it only be lit when the brakes are applied or all the time?

Should be lit (dim) along with the tail lights and bright when the brakes are applied. There are 3 wires going to the assy, tail lights, brake light and ground. Sometimes those wires break where the trunk hinges so check the harness first.

[AZLincolnMercury]

Do these Marks have neon 3rd brake lights?

My 97 Explorer does.....
They are very temperamental and very expensive to replace.

They wanted somthing like $400 to fix mine which works temporarily.

yeah, right

[ekooke]

"the middle rear taillight" is called the CHMSL, which is Federal (DOT/NHTSA) parlance for Center High Mounted Stop Light, the key word being STOP. In other words, it's an auxiliary BRAKE light. A cynic would say it's an example of the Fed pandering to the automakers and their "stylists", allowing the 'real' brake lights on the sides to be just about anything the stylists want, while still meeting safety requirements. :)
It's also wired separately from the primary brake lights, being wired directly from the BOO switch on the brake pedal to the CHMSL, while the primary brake lighting is routed thru the MF switch in a shared grounding arrangement with the turn signals.

[JaguarS4R]

Ok, so the middle rear talight should ALWAYS be on with along with the headlights/taillights, but as soon as I apply the brakes, the rear taillight just gets brighter

[ekooke]

Ok, so the middle rear talight should ALWAYS be on with along with the headlights/taillights, but as soon as I apply the brakes, the rear taillight just gets brighter

Well, a TRUE CHMSL shouldn't be on at all, until the brake pedal is depressed and the BOO switch is activated. The CHMSL bulb is a single filament one, unlike the double filament bulb used in most taillight/brake/turn combo bulbs.
Of course, the neon trunk lid light on a Gen II Mark VIII isn't a true CHMSL; I think that's a combo tail/brake setup and the "running" light should be on with the parking lights or headlights and then go brighter when the brake pedal is depressed. When the ballast on the neon starts to go, anything can happen, and you're looking at an $800 fix for proper operation.

[JaguarS4R]

Well, a TRUE CHMSL shouldn't be on at all, until the brake pedal is depressed and the BOO switch is activated. The CHMSL bulb is a single filament one, unlike the double filament bulb used in most taillight/brake/turn combo bulbs.
Of course, the neon trunk lid light on a Gen II Mark VIII isn't a true CHMSL; I think that's a combo tail/brake setup and the "running" light should be on with the parking lights or headlights and then go brighter when the brake pedal is depressed. When the ballast on the neon starts to go, anything can happen, and you're looking at an $800 fix for proper operation.

what is the BOO switch. b/c I have noticed that when I have the headlights set to AUTOMATIC, the rear peice doesnt light up, however, when I turn the parking lights or headlights in the normal position, then it'll light up

[ekooke]

BOO = Brake On Off

On the automatic vs. manual lighting thing, I don't know. Do the other taillights come on when set on automatic, or only on manual?
BTW, the most expensive unread book in the world is the owner's manual.

[Philip]

what is the BOO switch. b/c I have noticed that when I have the headlights set to AUTOMATIC, the rear peice doesnt light up, however, when I turn the parking lights or headlights in the normal position, then it'll light up

I'll bet that it is the harness, that was mentioned in here already. Mine did the same exact thing, but the weirdness continued to the point of the light going out when the trunk lid was raised (assuming the headlights are on therefore activating the running light part of it.) Would come back on when the lid was lowered as if it had a switch in it...lol.

I removed the harness and used a continuity tester to discover that both hot leads to the neon were broken, the ground was fine. The ground is also shared with the trunk release solenoid assembly and that was still working regardless. Replaced the harness, no problem. I got one from a crashed Mark, have no idea what a new one would cost or if it is even still available. You could rebuild the harness with low cost materials available at Pep Boys or WalMart, the harness plugs are easy to disassemble, and after the job is done, you can wrap it with electrical tape just like the factory in Mexico did (harness was made in mexico...lol. Ford parts all over the world...) It takes a little while to remove the retainers holding the upholstery panel on the lid, you want all this stuff to go back in place like it was :)

As far as autolamp or manual on settings on the light switch, I don't think that would matter the way the system is set up. That switch doesn't directly control the lights, it sends a signal to the SCIL (Steering, Column, Ignigion, Lighting Module) which does the actual business of lighting, etc. But this is a very comlex machine even for the 1990's, and anything is possible.

[UDL]

Ok, so the middle rear talight should ALWAYS be on with along with the headlights/taillights, but as soon as I apply the brakes, the rear taillight just gets brighter

yauza!

[Mr John]

The center lamp that goes from one side of the trunk to the other is a neon lamp. There is a 3 conductor connector inside the upper lining of the trunk lid. The connector is in there. The lamp works as follows:
It should turn on and light at about the same brightness as the standard red parking lamps. Then when the brake lights are turned on (by the BOO switch) the neon lights up as bright as the brake and parking lights. The light also lights bright when you press on the brake pedal even if the parking lights are no on.
Most of the problems in this light are in the ballast assembly, which is mounted on the lamp assembly. There are three wires going to this light. 1 ground, 1 parking lamp (from SCIL and also to all other parking lamps) and finally from the BOO or brake light switch. Sometimes owners will disconnect the connector instead of fixing or replacing the ballast because it normally shorts out the brake light fuse and it is easier to replace the fuse and disconnect the neon lamp. Ford charges over b$700.00 for a new lamp housing, However if there is no water damage to the light, there is a guy who builds the ballasts for $90.00, which is the easy way to go if your lamp does not work.

[Dave from SC]

The center lamp that goes from one side of the trunk to the other is a neon lamp. There is a 3 conductor connector inside the upper lining of the trunk lid. The connector is in there. The lamp works as follows:
It should turn on and light at about the same brightness as the standard red parking lamps. Then when the brake lights are turned on (by the BOO switch) the neon lights up as bright as the brake and parking lights. The light also lights bright when you press on the brake pedal even if the parking lights are no on.
Most of the problems in this light are in the ballast assembly, which is mounted on the lamp assembly. There are three wires going to this light. 1 ground, 1 parking lamp (from SCIL and also to all other parking lamps) and finally from the BOO or brake light switch. Sometimes owners will disconnect the connector instead of fixing or replacing the ballast because it normally shorts out the brake light fuse and it is easier to replace the fuse and disconnect the neon lamp. Ford charges over b$700.00 for a new lamp housing, However if there is no water damage to the light, there is a guy who builds the ballasts for $90.00, which is the easy way to go if your lamp does not work.

;) I just replaced the neon inverter in my 98 LSC . I got the replacement from Richard Mc Carthy , You can contact him at glitchm@hotmail.com . The unit is $ 90.00 including shipping it takes about 2 week to receive it once you place an order. Each unit is custom built so it does take time.
It comes with detail, but easy to follow instructions and pictures. The unit has adjustments to adjust the intencity of the break light.
and yes all break light work all times and the neon running light is present in light modes.
Dave from SC:D