headlights not working

[edvanland]

Help>  I am at Lake Powell and my head lights quit working.  I have 28 volt power to the dimmer switch.  The head lights are 12 volt.  The brights did work and not the Low beams.  Now none work.  My question is does anyone have a idea where the 12 volt power is picked up.  Under the left front access is what looks like a relay or mabey a voltage reducer. 
Any ideas or suggestions would help.  O yes it is a 1973 MCI 7.
Thanks
ED

[kyle4501]

They may be wired to 24 volts such that each light sees only 12 volts. If one burns out, they both go out. Use your ohm meter on the bulb to determine if it is bad.

Fix may be as simple as replacing the bulbs.

[gumpy]

Since the MC7 didn't come out with 12 volt headlights, you have somebody's modification (or bastardization, as the case may be). You're pretty much on your own on this one.

However, if it was modified according to later models which utilized 12v bulbs in series, then Kyle may have the answer (though if that's the case then they didn't complete the job as there would be a 12v safety circuit going in to prevent both bulbs going black when one burns out).

I'd suggest you pull the two outside bulbs and test the driver side connections with a volt meter and see what you have. If you have a proper mod, it should read 24 volts coming to it. Then put the driver side bulb back in and test the passenger side connection. It should read 12 volts. While you have the bulbs out, test them for continuity.

craig

[gus]

A friend of mine had his airplane landing lights wired this way. It was a 24/28v system with two 12v lights wired in series so that if one burned out the other one, even though it was good, didn't work.

This is the way old time Xmas tree lights were wired.

As has already been said, find out which one is bad and replace it. Both will then work.

However, it is possible you have a 12v tap somewhere off your 24v system, but the tests posted above will let you find that out. Since you have 28v at the dimmer switch it may have been bypassed to get 12v directly to the HL.

Let us know how this turns out.

[JackConrad]

Just a guess, but maybe the 28 volt dimmer switch controls 2 relays (high & Low beam) that have 24 volt coils and control 12 volt feed to the lights?  Jack

[edvanland]

tried allprocess of your most kind suggestions.  however none fixed the problem.  In the process now of running new 12 power source to headlights. Will use a three way switch as a high/low beam.  The old foot dimmer was very hard to use.  Will keep you posted as to the outcome. Would have rather been out on the boat, glad I have two people to do the work, I tried to help and was pused aside. O yes one is a retired fire dept fire engine machenic.
Thanks to all
ED
MCI 7 sitting on the beach at Lake Powell.

[JackConrad]

Will use a three way switch as a high/low beam.  The old foot dimmer was very hard to use.  .
Thanks to all
ED
MCI 7 sitting on the beach at Lake Powell.

Ed,
  That is what we did when I rewired our bus.  I eliminated the floor switch and used a double pole, double throw without a center off switch. Switch is either in high beam or low beam postion (no off position).  This switch is mounted in the panel to the left of the driver's seat. Jack

[bottomacher]

Jack- how do you turn your lights off?
Don

[edvanland]

We used a three postion switch mounted in the headlight position. Center is off up is HIGH and down is LOW.  Will see how it works. Now putting the bus back together.
Thanks ALL
ED

[BillC]

Hi, this could be as simple as a bad ground.  Bill C

[JackConrad]

Jack- how do you turn your lights off?
Don

The OEM headlight switch.  Since I already had the DPDT without center off switch on hand, this was the easiest way (saved a 25 mile round trip to town).  Jack