MCI-9 Road Light Relay ?????

[Kwajdiver]

JR,

Headlight Relay pin outs.  Battery is charged.

     Normal            Brights On

1    12.2                 0
2    26.8                 10.5
3    12.2                 3
4    12.2                10.5
5       .17               10.2
6    12                   4.4
7    0                     0
8    12                   10.3

[Hartley]

Uh... Hmmm...

It sounds like you have a dropping resistor in the headlight circuit.
If so it should be located in the lower accessory air tank compartment
up on the far left inside the curve of the sheet metal.

If it is a resistor it is probably bad. I had seen one other MCI that had
12 volt headlights and instead of using a 12 volt tap from the battery
they installed a load resistor in the headlight circuit and that's where we found it.

Now.. Let me clarify.. This information is only provided because for some strange
reason it seemed to ring a bell in my feeble brain. I don't remember where I saw this
nor whether it was an MC7 or 8 or early MC9....
I could be completely wrong too.. Maybe it was something else.. I dunno...

Dave.....

[Jerry32]

Which relay are you pinning out there ?? is that the headlite on or headlite hi lo relay???

[NJT5047]

This is gonna get complicated...but here goes.
The headlight relays are only for switching high/low grounds and the 12V backup system...they don't "supply" headlite voltage in a "relay" sense.  The headlight power comes from the headlight switch.  But, the ground is managed by the front "high beam" relay. 
Pin 3 is switched ground, but it grounds by connecting the RH headlight to the LH in series.  On high beam.   
This all assumes that your system is OEM MC9 with the 12V headlights in a 24V system.  They are wired in series.  So the readings you get on will vary by pin.  Pin 4 and 5 complete the low beam circuit, and pins 3 and 6 complete the high beams.  Pin 1 grounds the relay coil, and pin 2 is high beam call.  Pin 2 is the only pin that would have 24V, and only then on high beam.  If the bus is correctly wired,  pins 3,4,5,6 would have the resistance of one (or two filaments on high beam) headlight assembly.
The high beam relay is making grounds, not the power source. 
As Dr. Dave suggested, someone may have modified your headlight system to operate similar to a truck.  12V to each set of filaments with a ground on each headlight.
If you pull the LH headlights out where you can access the plug and check for 24V on low and 24V on high beam (only the LH headlight).   The readings should be 24V on both.  Check for a good ground on the RH headlight.  This is a common problem point.  Keep in mind, the headlights if OEM, are wired in series. The 12V cut relay will power up the remaining headlight if one filament burns out.   
If you find 12V on the LH headlight low and high leads, the system has been converted to 12V.  Probably.
Stud 28 in the FJB is the headlight supply and should read 24V on OEM wiring.   
If you have factory fog lights, the headlights must be in "headlamp" position to operate.   
The factory headlight system is complicated. 
What exactly is your problem with the headlights?  If one unit isn't working, the 12V backup is powering the remaining headlight.  This will confuse the H out of diagnostics.  If you have a bulb burned out, or removed from the circuit, the system will go into 12V default....should. 
Before you go much further, clean up the grounds and the 5 stud block that the wires are connected to.  Be careful with the diodes.  This assembly is right beneath your left foot, in the tool compartment. 
Now I'm confused....
Now I'm gonna say something that will get attention....If my headlights circuit failed, I'd wire it similar to a big truck.  No backup crap and all that complicated wiring.  The only issue is having to center tap the batteries for 12V.  Gotta have an equalizer....which I do.  That system would be as dependable as the aged bus systems.  These things can and will fail. Your your own guy, so what ever suits is good.  Just something to think about.  Do a nice wiring job, the 12V supply is at the 12V cut relay, and in the AC box.   If you get your headlights working well, no problem, but if not, well, that's been described above.  Some of our old buses have had mods to the headlight circuits and that should be considered and perhaps improved if necessary.   
Good luck dude! JR

[Jerry32]

I also might comment that the headlite system goes through the upper switch panel and has plugs to it that might get bad contacts as well as high resistance switches.  Jerry

[NJT5047]

JR,

Headlight Relay pin outs.  Battery is charged.

     Normal            Brights On

1    12.2                 0
2    26.8                 10.5
3    12.2                 3
4    12.2                10.5
5       .17               10.2
6    12                   4.4
7    0                     0
8    12                   10.3

There shouldn't be any voltage on pin 2 unless the high beam headlights are on. 
The pin 4 and 5 may indicate a bad relay.  If you're measuring to a good ground, 4 and 5 should be the same.   Otherwise, what you have on the High Beam relay looks almost normal.  The 4/5 thing should be rechecked.  Reading on 4, should be present on 5.  When 24V is on pin 2. 
May be some resistance in the contactors.  I'd replace that relay.  
Looks like the voltage supply is funky on high beams.   Still you are showing voltage on pin 2 which should not be there on low beams. 
I chew on this for a day.  Bedtime for Bonzo. 
Have you checked your dimmer switch?  They can be problematic. 
Get back from the relay and see if what is supposed to be present is measurable at another location?
JR

[Kwajdiver]

JR,

Thanks for the input and the time.  I will check all in the next couple of days.  Have been thinking about the dimmer switch.  I know they can be a problem.

The dimmer switch is located of course, left side near the front.  What is the push button, looks like a dimmer switch, left side on the floor next to the driver seat?

Driving down to Hot Springs National Park for the weekend.  Never been there, looking forward to it.....  I will check the voltages while there.

Thanks again,

Bill

[Jerry32]

The dimmer switch is nothing bu an off-on switch. it is off when lights are dim and on when on bright. What is does is power the hi low relar in the bright position and the hi low relay just makes the series connection to the headlights. Pin 1-8 are the 12V center tapp of the headlitss and are fed 12V from the center tap of the battery to insure proper operation keeping the lamps balanced and providing a path for an operation light if one in series fails.
Jerry

[Kwajdiver]

Hi Guys, I'm back....

Had to take a little work trip that was to be one city and two days.  Three cities, Saginaw, Mich, Champaign, Il and Atlantic Ciy, NJ and I'm back in Little Rock in the bus.

Have been working on the head light problem.  Cleaned all connection on the bus bar under the driver side lower panel.

On the relay, with no load, (wires removed on 3,4,5,6) 

I read,

pin 3  12 vdc
pin 4    0
pin 5    0
pin 6  12

Note Pin 2 is still reading 26vdc.  No matter what the state.

All other voltages are still the same, as when I started.

Should I order a new headlight Relay, where is the best place to order such an item.

Bill

[Jerry32]

Hey Bill, I don't have an mc-9 but it looks or sounds like the wiring is all about the same. As a mc 96 shows that pin 2 is the relay coil so that would indicate that the relay is activated.as long as pin 7 is ground. When in that mode then pin 4 and 5 are zero. so that would be correct. therefore pins 2 and 3 are powered to run the headlamps and are in contact with the 12 volts on pin 1 and 2 so what next as this should mean the high beams are on. Jerry