Headlight Short

[Altajones]

I own a 2018 Thor Miramar, model 34.2.

On occasion, when I hit a bump while night driving, my headlights blink, or go dark for 10 or 20 seconds. Typically, they will come on again, and I won't have the issue again for weeks.

We've replaced the headlight switch, the battery cables, and installed a new battery.

We've searched the electrical schematic, and looked looked in all the usual places to find the short.

Any suggestions for additional searches ??

[ducksface]

Those replacements are the three least likely things to cause this.
Go to an auto electrical shop and have them fix it.

You didn't tell us if
Brights
dim
Fog lights.
Drl
Dash
Cornering
Weather
Braking
Accelerating
If you've experimented in the daytime


There's an extremely good chance you won't find the loose connector or ground causing this,

[16ACE27]

You have ant intermittent OPEN, not a short. A short blows fuses, trips breakers, and/or burns up wires. Your open may be on the positive side wiring to the headlights or the negative side (ground).

[Altajones]

Sorry, I guess should have stated the obvious ... all of this work was done at my RV shop. Their tech is certified to do the electrical. Of course, I don't know how good he is, but I've always been satisfied with their work. They have been in business at that location for many years.

My challenge is that neither my shop, nor I, can get it to fail on command. They did multiple test drives over bumps and rough roads.

All, except one my failure incidents have happened while I was actually driving.
All of the blackouts are only for seconds. I have not had opportunity to get out, walk around the rig, and collect data ... wish I could!

I only had one incident during the daylight. I was in a campground and I was being assisted by fellow camper. I was experimenting with flipping all my switches in an attempt to cause failure. I got it to fail a time or two, but it was intermittent.
I could not make it repeat. I can't recall if my dash lights showed on, but I did experience one other strange thing .... my high beam indicator would appear on my dash, and my running lights would stay lit whenever my headlights went dark.
Your description as an "intermittent OPEN", is probably more accurate.
I appreciate your comments. Stan

[Chateau_Nomad]

Start at the lights that go out (headlights) and work backward to the power source. It could even be just a loose fuse. But... it could drive you nuts trying to find an intermittent problem. Are these the original factory installed headlights?

[Altajones]

Thanks for the comment.
Everything on the coach is original.
The Techs have tried all the normal tracing techniques.
Alas, to no avail. Looking for this needle in the proverbial 'hay stack', has really been a headache. It seems, as I mentioned earlier, we need to look beyond the usual suspects. I need them use their imaginations.
I'm searching for a new idea for them to try.
Thanks

[lwmcguir]

Replace the circuit breaker relay for the head lights

[Sappy2]

Probably a bad ground. Check teh ground wire back to chassis ground, or add a redundant ground to the lamps.

[javelin]

As you are finding out, some of the hardest electrical problems to solve are intermittent. You can’t fix what is currently working. Sounds like when you have your issue both regular and high beam headlights go out for a few seconds and then restore.....likely a loose or dirty connection somewhere. It could be anything including a loose fuse or a corroded loose ground connection in the head light circuits. You said “my high beam indicator would appear on my dash, and my running lights would stay lit whenever my headlights went dark”. Does that mean you were running with high beams on at the time of the total headlights failure........ or when you had the failure you tried flashing the high beams to try to restore some headlights and they did not come on; but you noticed the high beam lamp on the dash was working?


I don’t have a schematic for your headlight circuit, but if the high beam indicator comes on the dash during the few seconds you have a total headlight failure I would start looking at the common element for both regular and high beam units.......the “common ground” circuit. The high beam lamp on the dash probably uses the same fuse as what actually powers and lights the high beams, which would mean the wiring from fuse to high beam switch and dash is likely OK (famous last words). I could be wrong. but I think the ground between all front headlights is potentially a common connection between them bolted to a single ground point somewhere on the driver’s side front chassis near the rad. Make sure the headlight electrical connectors are physically clean and tight on the headlights and then try searching out the physical ground connection and trace it to the chassis bolt it connects to. Remove the bolt and clean the connection; restore it and make sure the bolt and star washer or lock washer tightens securely. If nothing else this will verify half the circuit is clean and good. Good luck.

[camperguy99]

Don't see anyone question the light bulb. Probably has LED lights so they can have open as well. Think it's a cold solder joint on the board where the LED's are soldered. I have experienced several of these cold solder joints. Many in the overhead light fixtures. I can usually heat the solder joints and restore operation but that may be above the OP's skill level? May have to replace the LED fixture? Maybe swap the fixture with one from the other side and see if the problem changes with the swap.

[Altajones]

I failed to post that when my headlights blackout, my emergency blinkers will operate as well as my running lights.
Would that indicate the relay as the problem, or is this just a educated guess?
I certainly don't mind taking an educated guess, but how will I know for sure?
If I could test the relay, and know for sure it was faulty, that would be great.
I'll ask the tech. Thanks

[ducksface]

If Your tech suggested the battery and cables as a cure...ask a different tech. That suggestion is very unconventional and unlikely.

I will suggest, until the repair is made, add a set of aux lights on their own circuit. If you hit the wrong bump and it causes a permanent headlight fail you won't see the ditch to get off the road and you'll be towed-in 'cause ya gots no lights.


My lightbar was an easy install behind the grill.

[16ACE27]

Originally Posted by Altajones

I failed to post that when my headlights blackout, my emergency blinkers will operate as well as my running lights.
Would that indicate the relay as the problem, or is this just a educated guess?
I certainly don't mind taking an educated guess, but how will I know for sure?
If I could test the relay, and know for sure it was faulty, that would be great.
I'll ask the tech. Thanks

Emergency blinkers and running lights are different fused circuits and different relays (if any). The headlight relay operates ONLY the headlights. Some vehicles have different relays for low beam and high beam.

[Altajones]

Thanks for your comments:
No, I was not running 'high beams', nor flashing another driver, when the blackout happens.
I provided the Techs an OEM schematic (which Thor sent me). They studied that to locate any common grounds. No luck.
When I had the one occasion of a daylight failure, I was able to test the flashers and the running lights. I haven't been able to repeat that situation.
Indeed, it does sound like a bad ground, but where!! Thanks again.

[Altajones]

That 'Lightbar' idea is a great suggestion.
(I allowed the new battery and cable idea to go forward because they are at the five year mark. Since they'd be due soon, I decided to give it a try.
Thanks

[ducksface]

posts 213 and 216 and 480, 724 are the post numbers in my signature thread for the light bar and install.

[OldWEB]

Could you post the OEM schematic you have? Different eyes, different ideas.

[Sappy2]

I forgot to mention that I think (not sure, would have to consult a wiring diagram) the head lamps are on a circuit breaker - auto reset. It could be an intermittent short tripping breaker and then the breaker resetting. Check head lamp wiring for any metal object contact points, pinches or rub thru's. I would focus on the parts that Thor installed (not under dash, rather under hood) Good luck.

[Beau388]

Agree with Sappy2. Detroit Chassis uses the Ford supplied wring from the head light switch to the steering wheel connector. Thor MC plant 850 use the front cap wiring harness to route the wiring from the steering wheel connector to the headlights. There are no fuses in the circuit only a auto resetting CB in the dash switch. This is specified by DOT lighting specification for vehicle external lighting. Parking, identification, clearance, marker and stop lights are fused and controlled through as series of relays. All but the stop lights relays are set by parking and headlight switch. On my coach, plant 750, the stop lights are LED and there is only a fuse in the main Ford distribution power center and the brake-light switch. There are no relays in this circuit.

[Altajones]

Originally Posted by camperguy99

Don't see anyone question the light bulb. Probably has LED lights so they can have open as well. Think it's a cold solder joint on the board where the LED's are soldered. I have experienced several of these cold solder joints. Many in the overhead light fixtures. I can usually heat the solder joints and restore operation but that may be above the OP's skill level? May have to replace the LED fixture? Maybe swap the fixture with one from the other side and see if the problem changes with the swap.

Thanks.
Yes, I think they are LEDs, but the reason I've not gone too far in that direction is because both lights go off and on simultaneously. They don't flicker at all. Usually, they just go dark for a few seconds, then they return perfectly. Still a mystery.