Brake lights

[dieselbob]

I know it’s not a tractor question necessarily but I working on one of my grain trucks getting ready for harvest. This is on a 1998 Ford semi tractor it looks like the Sterling model, It has brake lights on the tractor but not the trailer, when the park brake is set the stoplights are on like normal so that circuit is good, I have been looking for a couple days now for the brake lights switch I can’t seem to find it. Does anyone know where it is located? Is it part of the ABS controller? Thanks Bob

 

[joeysmith]

Not sure about that model but ford use to like putting them behind the driver's seat in the cab around the tractor protection valve
Usually hidden by a panel

Assuming this is air breaks

 

[dieselbob]

Yes it has air brakes. I will look closer tomorrow. I have looked on the fire wall both sides took the dash apart looked at the foot valve it’s mounted under the floor

 

[da.bees]

Are you saying that parking brake activates brake lights but foot pedal doesn't? Are you just trying to get brake lights on cab or adding trailer brake lights? If you can find wiring schematics for that cab it might answer some questions. There's obviously a pressure activated switch somewhere in air lines. Maybe instead of trying to follow wiring, follow lines looking for switch.

 

[dieselbob]

That’s what I have been doing following air lines looking for an air switch or air manifold that could have the brake light switch in it. I do have wiring diagram I’m going to test some relays tomorrow also, it would be nice to find the switch location and test that. Thanks for everyone’s input hopefully I find the issue soon

 

[joeysmith]

Seems like another spot they liked to put them was center of the firewall up high on the engine side
Been a few years since I worked on heavy trucks.
Good luck

 

[Mule Meat]

Don't overlook the pig tail connecter on the trailer.
Make sure the pins and sockets are not corroded, dirty or worn to bad for a good connection.
Clean them and use a small screwdriver to spread the pins a little to allow them to make good contact.

 

[jon f mn]

There is also a separate fuse for trailer brake lights in the fuse panel. That is usually in the box under the hood, but could be in the box inside the cab too.

 

[John M]

I dont have a clue, but I dont think Ive ever seen a semi that has the trailer brake lights on when the parking brake is set, and I see/have 15 - 20 a day back in my docks at work.

 

[matthies]

I dont have a clue, but I dont think Ive ever seen a semi that has the trailer brake lights on when the parking brake is set, and I see/have 15 - 20 a day back in my docks at work.

They are on when starting and until you build air pressure up.

 

[matthies]

I know it’s not a tractor question necessarily but I working on one of my grain trucks getting ready for harvest. This is on a 1998 Ford semi tractor it looks like the Sterling model, It has brake lights on the tractor but not the trailer, when the park brake is set the stoplights are on like normal so that circuit is good, I have been looking for a couple days now for the brake lights switch I can’t seem to find it. Does anyone know where it is located? Is it part of the ABS controller? Thanks Bob

The switch might be on the passenger side inside the cab, remembering an air manifold there, also the trailer receptacle has circuit breakers on the back side if it is in a six sided housing.

 

[John M]

They are on when starting and until you build air pressure up.

I have seen that on the truck, but not the trailer.

 

[matthies]

I have seen that on the truck, but not the trailer.

The job's 87 Ford L9000 and Mack Pinnacle 2016 semi's are that way.

 

[caterpillar guy]

Might just need the key on for lights to work.My Pete is like that no tail lights unless the key is on. For trailers. Got that from DOT inspections where they wanted to see the tail lights and brake lights and would not work till the key was on. Also is the plug to the trailer working some times the pins need to be spread with a small screw driver to open them slightly. I would use a charger on the trailer to test lights with a pin to touch each pin while a helper watches. The top big pin is ground ( White Wire).

 

[MARK ROBKE]

It has been a long time ago, but, I seem to remember there being 3 brake light switches on the L model fords. (We had a few in our fleet back then-late'80s-early '90s) Those Fords were peculiar in that the park brake set did have a switch for brake lights. The problem with that was when the engine was running with those lights on, it would overheat the bulbs and melt the lenses. But, back to your problem, I believe there were 3 brake light switches, all located on or near the foot valve on the firewall. I don't believe there were any relays involved, maybe only a fuse or a breaker. As far as I know, ABS controllers had nothing to do with brake lights, only dash warning lights. If there is an air manifold for firewall pass thru, it may be there. I would also check where the trailer plug passes thru the rear of the cab.
If the truck was mine, I would unhook the park brake, brake light switch. It would probably be easy enough to wire the tractor switch to operate the trailer brake lights too. Mark.

 

[dieselbob]

I found the switch it’s on the floor behind the seat on the drivers side, I located 2 switches replaced one that I thought was bad but didn’t help possibly bad replacement it had 3 terminals on it one ignition other two brake lights on trailer one of the trailer wires is energized when the park brake is pulled the other one doesn’t do anything no matter what is done, I made a jump wire from the other brake light switch to that dead terminal and it worked perfectly I still think the new switch is faulty. Thanks for everyone’s input Bob

 

[MARK ROBKE]

I found the switch it’s on the floor behind the seat on the drivers side, I located 2 switches replaced one that I thought was bad but didn’t help possibly bad replacement it had 3 terminals on it one ignition other two brake lights on trailer one of the trailer wires is energized when the park brake is pulled the other one doesn’t do anything no matter what is done, I made a jump wire from the other brake light switch to that dead terminal and it worked perfectly I still think the new switch is faulty. Thanks for everyone’s input Bob

I doubt the new switch is faulty. I think the 3 terminal one is for park brake, brake lights. The regular switches are easy to test : see if you have voltage on one terminal, and press the pedal to activate. Mark.

 

[Mcrafty1]

I dont have a clue, but I dont think Ive ever seen a semi that has the trailer brake lights on when the parking brake is set, and I see/have 15 - 20 a day back in my docks at work.

I have a Mack and it's setup to have brake lights on when the park brakes set and ignition switch on.

 

[John M]

I have a Mack and it's setup to have brake lights on when the park brakes set and ignition switch on.

All we have are Macks here at work. 14 of them to be exact. I have seen brake lights on when noone is in the truck, mostly in the mornings I have to come in at 3am or 4am. I guess Ive never seen one conected to a trailer and have the brake lights on, on the trailer, nor have I ever seen one with the brake lights on either the truck or trailer when backed in a dock idling waiting to be loaded or unloaded. I just looked at 4 backed in my docks right now. Other than normal lights, none of these have brake lights on. There is 3 Freightliners, and 1 Volvo and a 1 Kenworth and none of them have brake lights on.

 

[Mcrafty1]

All we have are Macks here at work. 14 of them to be exact. I have seen brake lights on when noone is in the truck, mostly in the mornings I have to come in at 3am or 4am. I guess Ive never seen one conected to a trailer and have the brake lights on, on the trailer, nor have I ever seen one with the brake lights on either the truck or trailer when backed in a dock idling waiting to be loaded or unloaded. I just looked at 4 backed in my docks right now. Other than normal lights, none of these have brake lights on. There is 3 Freightliners, and 1 Volvo and a 1 Kenworth and none of them have brake lights on.

I should of stipulate that my Mack is a 1986....in that era it was a mack thing, It was also the last year Mack trucks were thoroughbreds, after that they became mongrels...and may have ended the brake lights activated when the park brake was applied. idk