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Another Headlight Question, 3-5-2020
Even before we got our coach the headlights had been converted from the original 2 rectangular to 4 projector style headlights, similar to the the newer coaches. Additionally, the low beams have the HID hardware and bulbs and the high beams are halogen bulbs. I really like the HID low beams. They put out very good, usable, light.
The 2 problems that I have with the headlights that I have now is this. If you need to see a little further down the road, with no head on traffic, and select the high beams, the low beams turn off and you loose the very good light coverage up close. Worse than that, when you switch back from using the high beams to the low beams, the high beams switch off immediately but the HID’s in the low beams take a few seconds to “warm up” putting out very little light initially. Described another way, When you first switch from using high beams to low beams, rolling down the road at 60 MPH, the is very little light on the road (it’s dark!) for the first few seconds after you select low beams. The first time that this happened to me after purchasing our coach was a real, unpleasant, surprise.
What I would really like to do is to find a way to modify the the headlights to leave the low beams on even when selecting high beams. The low beams and the high beams would be on when the high beams are selected and the high beams would turn off when the low beams are selected. 4 Lights showing (high and low) when high beams are selected and 2 lights showing (low beams) when low beams are selected, like the newer coaches.
I was looking for input from someone here that has had their headlight wiring modified so that they operate as described above. In the meantime I will be studying the wiring diagrams.
Thanks
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29 Replies
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Something does not sound right. I have Prevost factory installed HID lights and they are better than my previous coaches and do not have a delay in switching back to low beams.
Who did the installation and did they use genuine Prevost parts? If so is the conversion installed correctly?
I am not a fan of some companies that do upgrades because of the quality of their work and that might be the problem which might require a good company to fix a poor job.
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Same thing on my 2015 H chassis. To put it bluntly, they suck when going from low to high and back. Exactly as the OP said. I posted about it awhile back, and if I remember correctly, Prevost said it was that way because of regulations on how much light can be put out at the same time? and could not be changed.
They are dangerous as far as I am concerned. It takes several seconds for the low beams to come back to full brightness each and everytime you make the switch.
I wonder if there are any good LED kits coming out that would be easy to do a swap out??
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Tim, we did what you are looking for here: prevostbumpertrims.com. Dalvin Pirtle is the owner.
We chose LED for the lows and the traditional bulb for the highs so there is no warm up delay any time such as when flashing. All four flash. Hi is all four. Lo is just the LEDs.
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Dalvin installs the upgrade in his shop for free if you go there. He also installs a diode in the front Prevost electric bay (steering compartment), but I forgot why.
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Jon,
I/m fairly certain that our headlight conversion was done quite a while ago (15+years) and is an aftermarket conversion. I’m just trying to improve the operation of the current lights and if the headlight buckets are Hella, considering a change to LEDs.
Mark,
I went back and looked at some of your previous posts (2016) as recommended, I found the one where “jbchevy3” posted photos of his headlights with “all 4 on” with high beams selected. I then searched the Prevost wiring diagrams for his serial number range (I guessed) and found some 2003-2004 H3-45’s chassis’s came from Prevost with headlight wiring that enabled “all 4 on” with the high beams selected. Out of curiosity I checked some other years and models and found that quite a number of coaches, H3 and XLII, came factory wired to enable “all 4 on” and even found some serial numbers equipped with low beam HID’s from the factory.
Dan,
Thanks for the lead to “prevostbumpertrims.com”. Your first hand knowledge and description of the conversion is helpful. Do you like the LED low beams?
Thanks all. I’ve looked a a lot of wiring diagrams lately and learned how Prevost wired the “all 4 on” on select VIN’s. I’ll investigate our coach wiring further before deciding what to do. Thanks again!
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I do like the LED low beams. They seem to produce a more natural color of light. Others have been critical of how far down the road they project. That may be correlated to their brightness. Brighter blinds oncoming more so projects less. Of all the choices available today, I would choose the same.
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I am sure if Mark says that is how the lights are mine operate with a delay in the brightness of low beams when coming from high beam. But I have never noticed the delay.
Maybe I am losing it and like Tom need to start driving something smaller.
Nope, not going to happen.
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Before everyone buys new lights you need to check your alignment.
It’s tricky adjusting the bulbs in the XL front bezel. Make sure someone helps that knows what they are doing.
My 06 was as bright as my 19. I’m aware of the delay but never a concern that I thought about or worried about.
Later
bv
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Who the hell still drives at night, that’s for sleeping and trips to your favorite restaurant.
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I drive at night all the time. We don’t hardly take a trip where we don’t do a fair amount of it. I found the old post. Seems in 2010 Prevost on the VIP shells changed it to not allow all 4 to be lit at the same time. Has to do with allowable light output with the type of lights being used.
I never followed up any further, but still would like to have them all on so the low beams don’t have to warm up all the time.
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Here is the thread from 2016:
2/21/2016 11:31:31 PMPrevostService 
High Beams Top of Page The vehicle electrical system is wired and programmed to have low beams or high beams only. Engineering tells us that if all four are on then they have too much luminosity (too bright) for us to make the coach like you want. That being said this may not cover all the years we have produced headlight systems. Plus there have been a lot of conversions to HID or Xenon lights by third parties that allow the 4 lights to be on.
As a manufacturer we are forced to build to required specifications at the time the shell is made. So if we do a retrofit of lights we stay with the engineering specification for that shell year. Third parties may be told to wire the lights this way but may not.
There are stated light intensities for any type of vehicle and Prevost builds to that requirement. Your lights are working as they were programmed to work from the factory.
And this was his follow up shortly after the above message:
2/22/2016 1:04:13 PMPrevostService High Beams Top of Page Just a little update on the post I made last evening.
The programming to cut off the low beams when the high beams were chosen on the H 3-45 platform only came with the use of the TYC lamp in 2010. It is used only in the H3 45 shells. On the X series we still use the Hella lamp and the low beams stay on with the activation of the high beams. Hopefully this will help!
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Whew! I’m glad you cleared that up Mark because I was hoping I wasn’t losing it by not noticing the delay in full brightness.
Now the original post needs to be re-examined to determine if something was done wrong with the conversion.
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So it meets the regulations but the man has to drive in the dark for several seconds to switch his lighting. Is there not a regulation that requires that the road be lit continuously? Cant he just change the signal wires on the lighting relays or something? I am no doubt displaying my ignorance on the complexity of newer coaches but this is bad news!
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I only researched the headlight wiring in detail on the 2000-2006 H3 and XLII coaches. No research on any multiplex equipped coaches. Any statement here is only applicable to the 2000-2006 coaches that I researched.
I have learned this:
The headlight conversion on our coach, as described above, was done in such a way as to cause the delay in the low beams from going to full brightness when going from, high beams selected, back to low beams selected. There needs to be another modification step or 2 to prevent the delay.
No coach, 2000-2006, “as delivered from Prevost” had this problem.
Prevost did install HID/Xenon low beams in some coaches. Any coach with the HID/Xenon option “as delivered from Prevost” had a “slightly different wiring” that prevented the delay in going to full brightness when switching from high beams to low beams.
Even some coaches equipped with Halogen low beams had the “slightly different wiring” like the HID/Xenon low beam equipped coaches. These coaches were more easily converted to HID/Xenon low beams and still avoided the slow low beam warm up when going from high beams to low beams.
It is my opinion that having 3-5 seconds of darkness when switching from high beams back to low beams with HID/Xenon low beams is NOT within OEM manufacturer acceptable performance or electrical engineering specifications.
It is my opinion that any coach that has this problem has been modified in some way after it left the Prevost factory.
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Problems Solved
DRL = Daytime Running Lights
A4O = All 4 Headlights on, low beams remain on when selecting high beams.
On our coach, the headlight conversion from 2 headlights to 4 headlights with HID/Xenon low beams and Halogen high beams left us with 2 problems.
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When switching from low beams to high beams the low beams would shut off and only the high beams would be on. Which works as intended. When switching from high beams back to low beams the HID/Xenon lights would take a while to warm up, leaving us with very dim lights for 3-5 seconds until they were back to full brightness.
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Our DRL’s were inop with the DRL relay/module removed. On our coach the DRL relay/module would light up the original halogen low beams with reduced voltage/current coming from the DRL relay/module but the transformer for the HID/Xenon light would not operate correctly at the reduced voltage/current. So they were disconnected by removing the DRL relay/module by someone prior to our ownership.
Problem #1 was fixed with a 3 amp diode added in the wiring to emulate/copy the way that Prevost did it with some coaches the were originally equipped with HID/Xenon low beams. Now when we switch from low beams to high beams we have both low beams and high beams on, A4O. When we switch back to low beams, the only the high beams switch off , just like Prevost did it.
Problem #2 was fixed with a change to the DRL wiring to to emulate/copy the way that Prevost did it with some coaches the were originally equipped with HID/Xenon low beams. Now our DRL’s light up the halogen high beams with reduced voltage/current just like Prevost did.
If you are interested in how we made the changes, look at the Prevost wiring diagrams for the Converted coach shell, XL2-45 MTH, 2004-2007,Unit Range 5-8359 – 5-8577, 5-8279, 5-8296, or 5-578 – 7-9095, Page 9.5, Exterior Lighting, in the Prevost technical documents online library and compare it to your headlight wiring. We emulated/copied the way that Prevost did it.
Too much detail?
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