Author Topic: Voltage on the high beam circuit.  (Read 805 times)

Roy Boles

  • BAC Member
  • *
  • Posts: 101
  • Thanked: 56 times
Voltage on the high beam circuit.
« on: January 05, 2024, 01:08:02 AM »
      Hi everyone, been doing some work in Beaver. I was replacing the headlights when I found that when the lights are on in the low beam setting I have about 5 volts on the high beam circuit. I have done the relay upgrade. I find that same volt reading on the feed circuit from the high beam relay. I have tested the voltage at the dimmer switch. Everything is working as it should at that connection. Any advice is appreciated.
'98 Marquis Diamante
C-12/Allison 4000

Steve Huber Co-Admin

  • Administrator Group
  • *
  • Posts: 3529
  • Thanked: 2716 times
Re: Voltage on the high beam circuit.
« Reply #1 on: January 05, 2024, 02:32:25 PM »
Not sure which electrical bay layout the 98 has. If it is the same as the 2000 chassis, suggest you disconnect the high beam connection on TB1-4 and determine if the 5v is present on the TB post or the wire. If on the TB post the source is between the relay installed in  the mod and the post. If it is on the wire, it is between the post and the hi beam bulb.

If your high beam connection is on TB1-3 (older electrical bay layout) use the same procedure. However, on this layout TB1-4 has headlight power so check for leakage between TB1-3 and 4.
2015-          07 Contessa Bayshore C9,  400 hp
2013-2015: 00 Marquis Tourmaline, C12, 425 hp
2005-2013: 01 Contessa Naples, 3126B, 330 hp

Eric Maclean

  • BAC Member
  • *
  • Posts: 1216
  • Thanked: 452 times
  • Karen and I would like to wish you all happy trail
Re: Voltage on the high beam circuit.
« Reply #2 on: January 05, 2024, 06:16:10 PM »
Check the headlight grounds as they all share the same ground if that ground goes bad they will feed back through the unused bulb seeking a ground each bulb will work as a resistor  lowering the voltage .
As Steve pointed out with the relay system in place and lights on check the feed circuit breaker to the relays for voltage ( should be 12 volts give or take)
If there is a difference of voltage on either side of the breaker you have a bad breaker.
Then check at either low beam feedforvoltage it should be close to that12 volts if not your wiring between the relay and the bulb socket is faulty.
Now check the ground side of the low beam bulb it shouldn't have any perceivable voltage if it does the ground circuit is at fault simple run jumper to a good ground and recheck if the reading is near zero volts then check the high beam for voltage with only the low beams tur ed old there should be no voltage at the highbeam ifthere still is remove onebulb and then the other to see if you've a bulb with afilement shorted across.

If with both bulbs removed you still have voltage at the high beam wiring unplug the high beam relay and check again .

If your coach is equiped will day time running lights a lower voltage is applied to the high beams any time the parking brake is released I believe Beaver used an aftermarket system made by hamsar for their DRL system. You should  find the DRL module in the electrical bay and it should have an inline glass fuse holder which feeds the module try removing that fuse and see if the voltage disappears.

Hope this helps
1997 Patriot Yorktown
2009 Chevy HHR
Roadmaster falcon tow bar
Demco Air Force one tow brake.