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Author Topic: Anyone have information on this (rectifier)  (Read 1218 times)
richard5933
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« Reply #30 on: April 13, 2018, 03:25:13 AM »

Looking this I think they were pulling half voltage off the Y connection of the alternator to power the low beams any time the engine was running and the lights weren't switched on. The diode was in the circuit to prevent backfeeding the alternator when the lights switched on. The Y connection would supply half the alternator's output voltage and it would be unrectified that is AC but the head lights don't care if it is AC or DC current. If you want to use this system, I would start at the alternator and check for the Y connection and trace the voltage forward and make sure you have the correct headlight switch. Good Luck.

Thanks - that's a good place to start. Once I have the energy to dig into this again that's where I'll start.
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Richard
1974 GMC P8M4108a-125 (Current Bus)
1964 GM PD4106-2412
Located in beautiful Wisconsin
KD9GRB
Oonrahnjay
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« Reply #31 on: April 13, 2018, 04:50:07 AM »

  Looking this I think they were pulling half voltage off the Y connection of the alternator to power the low beams any time the engine was running and the lights weren't switched on. The diode was in the circuit to prevent backfeeding the alternator when the lights switched on. The Y connection would supply half the alternator's output voltage and it would be unrectified that is AC but the head lights don't care if it is AC or DC current. If you want to use this system, I would start at the alternator and check for the Y connection and trace the voltage forward and make sure you have the correct headlight switch. Good Luck.

     This makes sense to me.  DRLs will last much longer (or a regular filament used as a DRL when the headlights are not switched on) if they're run at reduced power -- and also the light is a better marker with lower glare that way, for the same reason, low beams are good to use as a DRL.  At Land Rover, back in the '80s before DRLs got to be ubitquitous, for the N. American market we used a MOSFET clipper power reducer box with built-in backfeed protection and internal switching from the regular light switch.  Our solution was very similar to what Lee is describing -- it also means that you can't see the diode actively "doing anything" but if it's not there, under some conditions of lights on and dimmer switch in the wrong position, you could get backfeed.   That backfeed could mean the taillights might come on at lower intensity when you don't want them to, it could blow fuses, or give you odd sh*t like a trailer connector box burning out.  The fact that the diode doesn't seem to be doing anything could be the perfect reason that it's there and doing its job and all is well.
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Bruce H; Wallace (near Wilmington) NC
1976 Daimler (British) Double-Decker Bus; 34' long
6-cyl, 4-stroke, Leyland O-680 engine

(New Email -- brucebearnc@ (theGoogle gmail place) .com)
sledhead
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« Reply #32 on: April 13, 2018, 05:05:31 AM »

my day time running lights turn on when the parking brake is released to move the coach

Dave
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dave , karen
1990 mci 102c  6v92 ta ht740  kit,living room slide .... sold
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chessie4905
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« Reply #33 on: April 13, 2018, 05:24:21 AM »

check the wire colors and verify connections at each end. If that checks out, I'd disconnect each end of that wire and verify continuity with an ohm meter and temp looong leads. Check without or before diode, then check with diode in circuit. Diode should prevent current from headlight switch feeding back to R terminal on alternator.
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GMC h8h 649#028 (4905)
Pennsylvania-central
richard5933
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« Reply #34 on: April 13, 2018, 08:41:45 AM »

    ... The fact that the diode doesn't seem to be doing anything could be the perfect reason that it's there and doing its job and all is well.

When I said it doesn't appear to be doing anything I mean that the headlights don't turn on in DRL mode. However, after reading other comments, maybe they are designed to only turn on when the parking brake is released like in the MCI. I'll have to give that a try, as I only tried things with it sitting and running, not in moving mode. I'll chock the wheels and release the brake and see what happens.
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Richard
1974 GMC P8M4108a-125 (Current Bus)
1964 GM PD4106-2412
Located in beautiful Wisconsin
KD9GRB
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