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Author Topic: 12 volt headlights  (Read 1148 times)
uemjg
jerry
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« on: July 31, 2013, 02:43:14 PM »

My 1977 mci-8 bus has headlights converted to 12 volts.  Something is causing the high beam on the passenger side to burn up instantly and thus knocking out my low beams.  Suggestions?

I am also considering re-wiring the headlights, but I feel more comfortable if someone could share with me a good schematic of how it should be wired to include the dimmer switch.

thx.
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Jerry32
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« Reply #1 on: August 01, 2013, 06:04:45 AM »

Sounds like you are getting 24 volts to the high beams so not in series. lights inseries should have a 12 volt tap in the center of the config in case one blows out.
Jerry
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1988 MCI 102A3 8V92TA 740
pabusnut
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« Reply #2 on: August 01, 2013, 06:21:17 AM »

My '73 GMC 4905 was converted to 12V DC also.  I have a similar problem where all of the light are on, but some brighter than others.  It probably doesn't help that I am not sure I wired reconnected the dimmer switch wires correctly after I replaced the floor  Huh.

I hate to think about totally rewiring the headlight circuit, but it is probably the only way I will know that it is done right?!
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Steve Toomey
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belfert
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« Reply #3 on: August 01, 2013, 07:51:18 AM »

My headlights were wired 12 volts from the factory as were all of my exterior lights.  My main chassis system is 24 volts and the factory added an equalizer for 12 volts for the lights and other 12 volt stuff.  I bought Cibie headlights and put 24 volt bulbs in them.  What I did was used the original 12 volt headlight wiring to control a pair of solenoids that turn the headlights on and off.  I ran 24 volts directly from my batteries.  The reason I went 24 volts is the 35 foot long cable from my battery bay would have had to be twice as heavy with 12 volts to eliminate voltage drop.

You could do a similar thing with a bus that has 24 volt wiring for the headlights.  Any H4 headlight with replaceable bulbs can use 24 volt bulbs.  Yes, 24 volt bulbs are harder to find, but just order two or three sets of 24 volt bulbs from your local NAPA.  If you are going through more than two headlight bulbs in a trip something is wrong.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
Sam 4106
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« Reply #4 on: August 01, 2013, 08:44:45 AM »

uemjg, I have the instruction and schematic, from MCI, for rewiring from 24 volt headlights to 12 volt headlights. If you want me to send you a copy post your snail mail address and I will print a copy for you. Sorry, I don't know how to post them here.

Steve, if you went from round 24 volt headlights to rectangular 12 volt headlights you may just have to rewire the sockets. I went through the same problem on our MCI 8. The PO switched headlights without rewiring the sockets. When the headlights were on low beam they were dim and there was a glow in the high beam lights. There is a thread on this board somewhere about my ordeal. The sockets for round and rectangular headlights are wired differently.

Good luck, Sam
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
Ralph7
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« Reply #5 on: August 01, 2013, 09:07:31 AM »

      My 8 had been re wired, but had the diodes in place, under the floor of the driver, but wires were broken and corroded.
      First I redid the wires to the head lights(used original wires), then external powered the bulbs. You only need 2 wires (1 for hi N 1 for low) ---next remove the dimmer sw. 1 hot fused wire to the common post on the dimmer switch, 1 wire from the hi to a post 1 wire from the low to a post.
       The hot must be 12V. for me to prevent tripping breakers , I ran the hi of a relay and a relay for the lo. That means installing 2 relays and getting fused power(12V) from Huh?? and my dimmer switch controls the relays  not the bulbs.
       My house is 12V. so  it runs the coach lights.
       No matter how the head lights are (12V or 24V) the grounds are super important, must be very solid. 
        The sockets 1 wire to ground N 1 to the hi the other to lo---- some all 4 on lo when on lo and only 2 on high when on high.
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pabusnut
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« Reply #6 on: August 01, 2013, 10:10:59 AM »

Sam,

I have 12 VDC round headlights, but they do act like the square ones you describe.  I will have to do some more troubleshooting to see the extent of my problem.  For now I don't drive in the dark.
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Steve Toomey
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Ralph7
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« Reply #7 on: August 01, 2013, 03:01:02 PM »

           Mine are round 12V,  does not matter square or round. and I do not drive at night, but they work.
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chessie4905
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« Reply #8 on: August 01, 2013, 05:11:40 PM »

Some of the 4905's had a resister block to run 12 volt headlamps. It should be under drivers area in compartment, mounted to front inside near door hinges. There are 4 fat resisters mounted on a flat panel. with a harness plug.
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GMC h8h 649#028
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Sam 4106
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« Reply #9 on: August 02, 2013, 08:41:53 AM »

uemjg,

Jerry, I put the MCI 12 volt headlight information in the mail.

Good luck with your project, Sam
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
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