Have High Beams; no low beams

[HopLite]

Problem: I have high beams but no low beams

Symptions:
- light control switch twisted to tail lights - parking lights on
- light control switch twisted to head lights (i.e. low beam) - parking lights on, white front 'clearance' lights on, no low beams
- light control switch to head lights and pushed forward - parking lights on, white clearance on, hight beams on, no high beam indicator light

What I have done:
- Both 10A fuses are good
- I can hear the relay 'click' when the high beams come on...so I assume the relay is good (is that a wise assumption?)
- I did use this as an excuse for H4s and IPF housings
...the problem and symptoms still exist, so it definitely was not a burned out bulb
- I have checked the connections in the stock harness under the hood...the connectors are relatively clean and appear to make good contact.
- I have disassembled my steering column, checked the solder connections, and checked the copper contact switch for cleanliness...all are good (there are several threads on this...thank you). Manually moving the plunger on the copper contact switch did not turn on the low beams but did turn on the high beams. Is this switch only for high beams? That was my thinking as the plunger is activated by the flipping forward the lever.
- I have checked the two grounding points near the fuse box...both are very clean and tight
- I have inspected the wiring loom that runs beneath the steering column for cracks in the wire's insulations or anything else that could cause an electrical problem...everything was surprisingly clean, no wires had crusty insulation, and everything seemed on the up and up.
- All connections in the wiring loom that runs beneath the steering column were tight.

Question: Is there anything left to check that I have missed? Is my best route from this point to replace the light control switch (if so...know anyone who has one that works)? I have not checked the high indicator bulb to see if it is burned out...but in looking at the schematic that should not matter as the circuit would still be grounded through a theoretically functional light control switch.

Looking forward to some thoughts. From where I sit, I'm running out of options. She's my daily driver and I've had to tape about 60% of my nice bright new high beams to not blind any oncoming traffic. Trying to keep the night (or morning) driving to a minimum as I don't want to overheat the new bulbs (the tape keeps the heat in...).


Thanks in advance.

 

[slcfj62]

Your symptoms are the exact symptoms of both low beam headlights burned out. The fact that your high beams work says that your headlight relay and the fuses and the 12 volt wires to the headlights are all good. The High Beam Indicator gets it's 12 Volts from the ground side of the low beam headlight elements which "float" to 12 Volts when you switch to high beams--switching to high beams removes the path to ground for the low beam elements. The High Beam indicator lamp has it's own path to ground, so if 12 volts is at the headlights (and it is), and if the HI/LO switch is in the High position, then the High Beam Indicator lamp will come on unless both LO Beam headlight elements are burned out, or unless the High Beam Indicator lamp itself is burned out. So the most likely culprit is both LO Beam elements are burned out. The fact that you have tried replacing your headlights with H4 IPF headlights and obtained the same results is a bit puzzling. If it were me, I'd go invest $10 in one el-cheapo stock sealed beam headlight at your local auto parts store and try that. If that still doesn't work, then you are going to have to troubleshoot with a volt meter to find out where the break is. It will be somewhere between both headlights and the connector at the bottom of the steering column.

 

[sirenmoses]

^ the above.

just submitted a work order on a fire apparatus for the same problem: stuck on high beam when shoulda been low/off.

happens on occasion w/the older rigs, both fire and 'yota.

 

[HopLite]

So...
The wiring and switching on the vehicle harness are all good. I confirmed this by bypassing the headlights with an cheapo "12v work light" and essentially using that light as a 'test' head light to cycle through the wiring and switch configurations. In my earlier attempts at trouble shooting the vehicle harness, I used an LED...not a good idea as it did not provide enough resistance to allow the current to flow according to the design of the circuit. Plus, the LED gave false feedback because it lit up with the slightest difference in potential...essentially lighting up when it shouldn't have.

Also, I was able to confirm the cause of my initial problem...both OEM low beam filaments simultaneously burned out. This confirms our initial suspicion but does not explain why the new H4s did not fix the issue.

Also, I was able to confirm why the new H4 low beams did not light up...they operate on switched supply, not switched ground. Because the truck works on constant supply and switched ground, there seems to be a communication problem between how the truck wants to control the lights and how the lights want to be controlled. So I'm off to search the solution to this. Hopefully there is some snazzy wiring trick that does not involve buying different bulbs.

 

[Michael Hanson]

Stem switch. 2 cents MIke

 

[HopLite]

Eh?

 

[2mbb]

LED lights care which terminal is +12V and which is ground. Normal filament lights don't care as the electrons will flow either direction. I'm not sure about the H4 bulbs. If you can operate the bulbs "backwards" then you may just have to rearrange the pins in the headlight socket.

 

[HopLite]

Right...LED's are direction specific (direction meaning +/-). The problem with LEDs is that they are so efficient that they require a very small voltage difference to create enough potential for the electron flow. The normal incandescent bulb is less efficient and needs a greater potential to light up. There were instances in which the LED would light up but the incandescent would not. There was enough potential difference to light up the LED but not the incandescent.

In troubleshooting my switches and wiring, there was one instance in which the LED gave me false info because of its efficiency...but using the cheap 'work light' incandescent bulb cleared things up.

So in my mind, LEDs are great to figure out if there is any juice in a line but can be misleading if you are trying to figure out if the line has enough juice for the circuit to do its job. And using a DMM would have been the more scientific way of going about things.