BRIGHTS cause loss of headlights!!

[bamaboy473]

Headlights work fine. So do the fogs. However, it's deer season and we want as much light down the road as possible, so I used the high beams/ brights for the first time and....and everything went Dark after about 8 seconds

For whatever reason other than fear, I turned the switch Off and On again and the lights came back on, but no high beams. I flicked the brights (high beams) On again and same thing happened.

Since getting back to the house, turning brights On caused everything to go dark every time, and the time interval delay is 8-12 seconds, every time.

Could there be a thermal fuse that's self-setting in that system? What would you do to diagnose and fix the problem?

[Pigman1]

You have a short in the high beam circuitry somewhere. When you go to high, the circuit breaker trips so you get nothing. The CB is an auto reset so when it cools down, you have high beams again for the short time it takes for it to blow again. Looks like you need a meter and some time to find out where.

Good luck.

[bamaboy473]

I agree with your analysis and would have written about the same thing, based on what happened...repeatedly, but I have no clue about Why a thermal breaker would be installed on a high beam circuit...Where it would be (on two lines, or near the switch, or What it would look like.

My trusty meter needs a bit more information about What and Where before I can report back with results. Can somebody help define my target?

[mdpuff]

This is a safety design that has been built into head light switches for a very long time. There is a thermal over load "Breaker" built into the head light switch that will shut off the head lights for a short time then reset if there is too much load on the system such as the high beams. If the system was fused then you would lose you head lights completely till the fuse was replaced. Over time the thermal beaker can get weak and trips when the high beams are on as they draw more currant than the low beams. (driving lights are on a separate circuit) To test you need an ammeter to check the draw from the high beams and if they are within limits (not sure what the spec's are but around 10 amps would be ball park) then try a new head light switch and that should cure the problem. I suspect a weak thermal breaker in the head light switch assuming your high beams work properly. I have run across this issue a number of times in the past and a new switch should cure the problem. It is much easier to replace the switch to test the system rather than chasing your wiring. It's always a good idea to check all your grounds in the system just to be safe, bad grounds can cause high loads in a circuit.

[bamaboy473]

Thanks for the education. We have a few hours before the games start, so I'll do a little digging under the dashboard. All wiring to the lights looks proper.

Wish me luck!

[bamaboy473]

UPDATE: First off, we don't get to our headlight switches by simply slithering under the dashboard. Nope, we get to dis-assemble everything on Top in order to access the switch. Why ME, lawd??

Seriously, all of this stuff is fastened with screws, so it's a matter of finding them and removing same. About an hour's worth of work, including finding those hidden gems (see photo 3)

The switch is held to the faceplate with nuts and screws. Said nuts turn, which is why you need absolute access to the back of the dashboard, and eyes to see the whole assembly.

Now that I have it in my sights, I have two questions:

1. Can the switch itself be bench-tested without power to it? Doubt it, but have to ask, and

2. Where to source the switch? It's design demands an exact match.

IF no replacement exists, can the switch be repaired?

Here are some photos of the project:

[Gary RVRoamer]

I'm not sure it's a given that the switch is also the circuit breaking device in your coach. In modern vehicle systems, the headlamp switch usually drives a relay to switch power to the bulbs anyway, so the actual current measurement would have to be at the relay or the power source rather than the switch.

Seems to me that a separate auto-reset breaker is going to give the same symptoms if the overload is marginal. A direct short would trip the safety immediately, so it is probable that your highs are on the borderline of the current limit and it therefore takes several seconds to pop.

Maybe someone at Thor Motorcoach could tell you where the breaker is located, or at least whether it's part of the switch or a separate device.

[bamaboy473]

Gary, I call your thoughts, and raise by questioning whether the stalk that activates brights (and isn't part of the headlight switch) should or shouldn't be considered in the equation.
I have the switch at my desk and an going to start trying to source it. Even if a used one, replacing is what guys like me do in the absence of knowing how to properly diagnose the system. I'll make a call to Freightliner before I do that, just in case they know something I can use.

In the meantime, I'm going to disconnect one bright, then the other one, to see whether half draw makes a difference. Thanks for your advice.

Originally Posted by Gary RVRoamer

I'm not sure it's a given that the switch is also the circuit breaking device in your coach. In modern vehicle systems, the headlamp switch usually drives a relay to switch power to the bulbs anyway, so the actual current measurement would have to be at the relay or the power source rather than the switch.

Seems to me that a separate auto-reset breaker is going to give the same symptoms if the overload is marginal. A direct short would trip the safety immediately, so it is probable that your highs are on the borderline of the current limit and it therefore takes several seconds to pop.

Maybe someone at Thor Motorcoach could tell you where the breaker is located, or at least whether it's part of the switch or a separate device.

[Gary RVRoamer]

Good point about the Hi/Lo stalk/switch. Nor am I sure what pieces, if any, Freightliner supplies to Thor. Mine has a Smart Wheel supplied by FCCC, and the Hi/Lo beam selection is done there, so it must be a trigger for a relay elsewhere.

[bamaboy473]

Do headlights come in LED configuration? If my high beams are drawing too many amps, wouldn't LEDs eliminate that?

[bamaboy473]

UPDATE: Here are photos of the headlight switch. I didn't see anything that resembles are thermal fuse, so closed it back up and think I need to put the switch on the shelf pending more searching in the headlight compartment.

Question?? I don't have a Smart Wheel and the Bright Beams are activated by one of the stalks on the steering column. The cable connects to the harness with a 4-wire multi-connect....and that harness looks like a clump of spaghetti.

Assuming that a thermal fuse wouldn't be placed in the midst of the harness, could somebody describe what one would look like, and a probable place for it?
Would a manufacturer place such a device Outside the coach (like in the front area by the genset)?

[bamaboy473]

mdpuff, I wonder whether your suggestion would remain that way in the face of my coach having the Bright switch on a stalk attached to the steering column?

Originally Posted by mdpuff

This is a safety design that has been built into head light switches for a very long time. There is a thermal over load "Breaker" built into the head light switch that will shut off the head lights for a short time then reset if there is too much load on the system such as the high beams. If the system was fused then you would lose you head lights completely till the fuse was replaced. Over time the thermal beaker can get weak and trips when the high beams are on as they draw more currant than the low beams. (driving lights are on a separate circuit) To test you need an ammeter to check the draw from the high beams and if they are within limits (not sure what the spec's are but around 10 amps would be ball park) then try a new head light switch and that should cure the problem. I suspect a weak thermal breaker in the head light switch assuming your high beams work properly. I have run across this issue a number of times in the past and a new switch should cure the problem. It is much easier to replace the switch to test the system rather than chasing your wiring. It's always a good idea to check all your grounds in the system just to be safe, bad grounds can cause high loads in a circuit.

[gemini5362]

Originally Posted by bamaboy473

mdpuff, I wonder whether your suggestion would remain that way in the face of my coach having the Bright switch on a stalk attached to the steering column?

I am not an RV mechanic so I am not saying I have positive knowledge of RV light switches. However they appear to be the same thing that is on cars or pickups and I have played with those a lot. I am going to be very surprised if you have a breaker in your light switch. The other poster is correct almost all light switches control a relay. The ones that I have seen which don't were from 60 model possibly 70 models that had the dimmer switch on the floor. Every one that dimmed from the steering column had a relay. The breaker that he is talking about should be a regular fuse mounted breaker. If you look in the fuse box you should find the breaker for the lights. I am not clear about one thing in your description of the problem. If your bright lights go off for a short while can you go to the dim lights and are they still on or do they shut off also. IF they are still on you can replace the relay first if they are not on replace the breaker. If that does not fix it start looking for a short in the high beam wiring.

[bamaboy473]

Originally Posted by gemini5362

I am not clear about one thing in your description of the problem. If your bright lights go off for a short while can you go to the dim lights and are they still on or do they shut off also. IF they are still on you can replace the relay first if they are not on replace the breaker. If that does not fix it start looking for a short in the high beam wiring.

I can run low beams and fogs with no problems. From 5-12 seconds after I turn the high beams ON, everything shuts off (high and low beams). A wait of 6-8 seconds, and they all come On again, only to repeat that dance until I turn the High beams Off, at which point low beams run like they're supposed to. So do the fogs.

A PM from mdpuff has me looking for LED bulbs for the high beams. They will draw less current and might resolve the overload problem; at least I think they should. If not, I still have better lighting.

I'll start checking out relays tomorrow. Thanks for the help.