Any help for dim headlights?

richard5933 · October 23, 2018, 11:34:42 AM

OK - I give. Can anyone point me to the place where the headlights make their ground connection?

For that matter, there are supposed to be a couple of grounding lugs in the electrical compartment next to the driver. Can't find them either.

Also - I have the resister panel in the tool compartment, but there are not any breakers like the manual shows. Anyone know where they are?

richard5933 · October 23, 2018, 12:04:09 PM

Voltage at batteries with engine running and lights on is 27.11v and at the dimmer switch is 26.0v.

Obviously a voltage drop. Not sure if it's a normal drop or the cause of the problem, but for sure it's not helpful.

I measured at the dimmer for two reasons... 1) It was handy, and 2) it eliminated any problems from the as-yet not found ground connection for the headlights.

Regardless, the wiring to the headlights looks really clean and everything seems tight. I know, that's going to be the car until I find a problem. Now on to go search for problem areas and/or bad ground connections (if I can find them).

luvrbus · October 23, 2018, 12:38:11 PM

I have no idea about head light grounding on a GM bus that said some buses the lights are relay grounded that confuses the hell out of me

richard5933 · October 23, 2018, 01:05:59 PM

I don't think that there is a relay in the circuit. Seems like the headlights are wired directly to the switch.

The only things I see in the circuit are:

Circuit breaker > Switch > Dimmer Switch > Circuit breaker > Low Beam
> Circuit breaker > High Beam

Can circuit breaker cause a voltage drop? Do they fail slowly or all at once?

UPDATE: I found the ground posts in the driver's electrical panel. Those are both tight and clean. Looks like the ground from the headlights is there.

I've thought about adding a relay, but where would it go? Would it help to add relays since the wiring run is really pretty short - just from the driver's electrical panel to the headlights?

Or, what about increasing the gauge size on the wiring? Right now it looks like the entire headlight system is wired using 16 ga wires. There appear to be separate circuit going to each headlight though, and no one light appears to carry more than 5 amps. From the charts online, 16 ga wire can carry 5 amps the required distance with only a 3% voltage drop. That might be what accounts for the voltage drop, so maybe going to 12 ga would reduce the voltage drop and increase the lighting.

One more thought - today I checked the voltage drop and found 27.11v at the batteries and 26.0v at the feed to the headlight dimmer. What I did not check was the voltage at the driver's electrical panel main feed buss. Guess that would be something important to check, and it's on my list for tomorrow. I want to check to see if the drop is between the batteries and the electrical panel or between the electrical panel and the headlight circuit. If it's in the headlight circuit it's easier to fix. If it's between the rear and the front of the bus then it will be a more difficult fix.

In other words, I'm really confused about this and don't know what to do first to make things better. Rather than guess, I'm doing nothing for now until I come up with a workable game plan that will actually improve things.

chessie4905 · October 23, 2018, 04:33:47 PM

You have 12 volt headlights. That is what the resistor panel does. Check a headlight bulb, it should be marked 12 volt. That panel should have multiprong plug that plugs into coach harness. at top of resistor panel are your circuit breakers.Check your wiring diagrams. The ground connections come off at headlamp bulbs, not under driver's compartment.

Now there is the possibility that you have the panel, but still have 24 volt lamps. If so, the harness coming down towards the panel will have a plug with short looped stub wires, and resistor panel is not plugged in. If that is the case, unplug stub and plug panel into it and change 24 volt headlamps to 12 volt.

richard5933 · October 23, 2018, 04:55:21 PM

Quote from: chessie4905 on October 23, 2018, 04:33:47 PM
You have 12 volt headlights. That is what the resistor panel does. Check a headlight bulb, it should be marked 12 volt. That panel should have multiprong plug that plugs into coach harness. at top of resistor panel are your circuit breakers.Check your wiring diagrams. The ground connections come off at headlamp bulbs, not under driver's compartment.

Now there is the possibility that you have the panel, but still have 24 volt lamps. If so, the harness coming down towards the panel will have a plug with short looped stub wires, and resistor panel is not plugged in. If that is the case, unplug stub and plug panel into it and change 24 volt headlamps to 12 volt.

Are you certain about this? I thought that I measured the voltage at the headlights when I first started this thing and got something around 25v. Possibly the high beams were on and I was measuring across two hot terminals?

If what you say is correct, then I should measure approx. 12-13v at the headlight socket, correct?

There is a loom of wires coming from the resistor panel, and it does go through the multi-prong harness plug like you mention. No looping of wires. It does seem that the circuit breakers for the headlights are all located in the driver's electrical panel on this bus, not above the resistor panel.

Funny thing is that the resistor panel is not anywhere in the wiring diagrams, at least not that I can find. Sure would make the solution easy if that is the entire problem - nothing more than a trip to the local parts store to get the proper sealed beam lamps.

richard5933 · October 24, 2018, 05:12:19 AM

With engine not running (but battery charger on), headlight socket has 9.8v. I'll put the block heater on later today and start to engine to see what the reading is with the generator and all circuits fired up. I know that the headlights are noticeably brighter with the engine running.

Regardless, it does seem that chessie4905 hit this on the head - resistor panel is reducing voltage to the headlights to 12v. The headlight bulb is labeled 12v.

So, now my goal is to figure out how the resistor panel is wired into the headlight circuit. First I'll see if there is a bad connection somewhere. If that doesn't help I'll try to figure out how to replace the resistor panel with something more modern to provide proper 12v to headlights.

If you look at the photo of the resistor panel I posted earlier, you'll see that there are lots of wires coming to/from it. The resister panel is somewhere in the circuit after the dimmer switch. I've got to figure out where things go after that. I know that the four circuit breakers are 5-amp each and mounted in the driver's electrical panel. Not sure where things go from there, but I'm assuming to the resistor panel.

Still looking for a wiring diagram for this if anyone has one they can snap a photo of.

luvrbus · October 24, 2018, 05:42:47 AM

I know you like to keep things original but resistors are a poor setup for headlights,your getting 9 volts now in hour of running when they build heat that will be 8 volts .I would be looking for another option like a 24v Vanner and use the 12v supply from it

richard5933 · October 24, 2018, 05:48:29 AM

Quote from: luvrbus on October 24, 2018, 05:42:47 AM
I know you like to keep things original but resistors are a poor setup for headlights,your getting 9 volts now in hour of running when they build heat that will be 8 volts .I would be looking for another option like a 24v Vanner and use the 12v supply from it

Actually, I am looking to replace the resistors. This would come under the category of safety equipment, which I have no problem replacing with modern equivalents.

For simplicity, I think it would be easiest to just replace the resistor panel with a modern 24v-12v converter. Problem is I have no idea how the current panel is wired into the system. There appear to be 6 wires in and 6 wires out. Where are they coming from and where are they going to?

Best I can tell, the resistor panel sits between the final circuit breakers and the headlights themselves. No certain on that and will have to do additional checking. I'd like to avoid rewiring the complete headlight circuit, and hopefully someone will have information about how this thing is currently wired so I only need to adapt what's necessary to modern parts.

Keeping the 12v headlights is certainly a goal though, as they can be found anywhere should I ever need one.

richard5933 · October 24, 2018, 06:02:54 AM

I'm thinking that one of these should do the trick. Probably overkill for now, but if I upgrade the lights to something better down the road I'll be ready.

https://www.donrowe.com/Samlex-SDC-30-DC-DC-Converter-p/sdc-30.htm

Now if only I knew how that resister panel fits into the wiring harness so I don't blow something up replacing it.

luvrbus · October 24, 2018, 06:04:39 AM

GM had a thing about using resistors just amazes me they did it on a headlight system,I remember the problems they were on the 55 Chevy's going from 12 to 6 v on the coils

buswarrior · October 24, 2018, 06:47:08 AM

A little snug on capacity, you are at the rating with 4 x ~75 watt bulbs burning, easy to do with good high beams.

Remember who was maintaining that coach after it left the factory... a collection of characters who were, for the most part, unsupervised. The lights were working once the greasy hands were done, that's all the foreman cared about, but the methods used to achieve that...

Many techs, when faced with a problem in the headlights, would change it over to whatever they liked, there was an ample supply of 12 and 24 volt parts lying around the garage back then.

Expecting to find a stock configuration at this point...?

I like Cibie brand too, excellent optics, puts the light where it belongs.
RJ prefers the E-code ones, if he would get off FB and join the real busnuts on the forums, more often, he would tell you himself...

happy coaching!
buswarrior

Quote from: richard5933 on October 24, 2018, 06:02:54 AM
I'm thinking that one of these should do the trick. Probably overkill for now, but if I upgrade the lights to something better down the road I'll be ready.

https://www.donrowe.com/Samlex-SDC-30-DC-DC-Converter-p/sdc-30.htm

Now if only I knew how that resister panel fits into the wiring harness so I don't blow something up replacing it.

richard5933 · October 24, 2018, 07:18:22 AM

I spoke with Luke this morning. He thinks that this an option installed at the factory. Unfortunately, he says not all options made it into the wiring diagrams.

Looks like four wires go in and then out of the resistor panel. I'm guessing that they separated out each of the four wires in the system (left low, right low, left high, & right high) so that any failures could be contained to the single lamp.

I'm going to verify later today. If this is correct, then it seems I could either use one larger voltage reducer upstream, or use four smaller ones to replace the resistors, maybe 20 amps each.

For now I plan to keep as much of the existing wiring in place as possible and continue running the 12v sealed beam lamps for now. But, by getting the right voltage reducers I'll be able to upgrade the wiring and lamps down the road.

eagle19952 · October 24, 2018, 07:57:31 AM

We used imilar DC/DC converters on 24v Cat/Dirt eq. to power 12v Motorola Com radios.

I would remove the resistor and use one after I eliminated all other possibilities.
It sucks to tear out and have the same problem when you are done.
Worst case, I would power the bus lamps with my truck source 12v or a 12v battery on a good charger and troubleshoot.

chessie4905 · October 24, 2018, 10:51:55 AM

I may be full of sh*t on the 12 volt option. Those resistors may be for daytime running lights running at reduced brightness. Do you have them? When I get a chance, I'll check the wiring diagrams to determine one way or the other.