I checked another source on headlight voltage requirements. It says 13.2 volts minimum and discusses exactly what you say about percent loss and says the same. It also talks about headlights being underwired on older vehicles.
I am going to install continuous duty solenoids which will be powered by the headlight wiring to turn on/off and wire power directly from a 14v battery power source under the hood. That should fix my issue I hope. Unless someone tells me otherwise. We will see and let you all know.
Thanks for the great info. You are all awesome and have been great help!
You shouldnât have to do what youâre proposing . . .
I think the best solution is to find where youâre losing voltage . . . and fix it . . . and you wonât have to modify anything
As I said, those sealed beams arenât the greatest, but if theyâre getting around 14V at idle with the headlight switch on, that should be sufficient
That website I mentioned has the complete headlight wiring diagrams, so you should be able to measure from the battery, through the switches, all intermediate connections, fuse boxes, etc., all the way to the sealed beams
After my last post I thought to myself, you know I really should go back to tracing the system to check the cause of the loss before I add solenoids. If I can find? Although as I mentioned, another site notes the wiring is often undersized on older vehicles. Since the issue is common to two like vehicles, I am thinking it is a common issue and that leads me to believe more likely wire size than a bad connection. But I will do more investigation before I do the ultimate easy lazy man fix. Plus, I really havenât had the time to get into checking the system yet so I probably should do that before anything else. You donât think I should be lazy and I agree.
Speaking as a professional . . . and letâs also mention that our fleet has quite a few Kodiaks and Topkicks that donât have the problem yours do . . . makes me think âbad connectionâ rather than undersized wiring
I donât mean to sound like Iâm nit-picking or being disagreeable . . . itâs just that my sample size, so to speak, is quite large, and includes several trucks just like the ones in your fleet
An easy way to see if you have a faulty connection to ground is to measure the voltage on the return side of the light while it is ON, using a known good ground point as your meter reference. If you see more than .3 volts at that point then you need to check the grounding to the light. If the reading is close to zero volts on the return side then the supply side needs to be checked. You can compare the readings to the other side of the headlights for a reference voltage. If the supply voltage is slightly lower on the bad side then follow that wire. There may be separate relays for each side of the lights. If so, I would first suspect the relay socket or relay as the cause of the bad connection to power and where the voltage drop is occurring. If there are separate relays for the lights try swapping them to see if that changes things. If that is okay then any other connector points in the circuit should be looked at for the problem. Having a factory service manual for the wiring is a big plus to have for reference for these kind of problems. Ebay is a good place to get them.
Traced power as far as the headlight switch and show 14v in 13.8/13.9 out. Also checked the headlight connection pigtail and it test good. I will look to see if there are any connections between dimmer switch and headlights that I can test. Then I will have to figure out how to get to dimmer switch on the column. That is for another day, Nice day today and I have things to do around the home.
Cougar, going to have to study your post a bit to understand. One comment I have is both headlights are dim, not just one and dim on bright/dim/DRL Plus I already ran a new ground to test and made no difference. Not sure if there are relays on the headlights. If so, I havenât found yet. db4690 comment above referenced a website which gives wiring diagram info and I am using that. Donât see a relay on that except for DRL.
Thanks.
Since adding a new ground connection didnât make any difference that means the ground to the lights is okay, assuming that the new ground point was good.
I was confused about the lights. Since both lights appear to be dim the same amount and you have slightly less than full battery voltage at the lights my guess is that the issue are having is due to normal wire losses. Which you found some reference to. The wire losses will be in the supply wires to the lights, not in the switch wires. The switch controls the relays, which handle the higher current needed by the lights. The lighting control switch just needs to handle a small amount of current to control the relays. The relays are most likely in the fuse panel under the hood.
My earlier post was about just trying to help you locate voltage drops in the light circuit. Anytime you have extra resistance in a circuit where it shouldnât be, and current is flowing through it (lights ON), a voltage drop will occur across that added resistance that shouldnât be there. That voltage drop will cause less voltage to be across the load, or light in this case. It is a series circuit. All the current of the circuit has to pass through anything that is in that series circuit, including the extra resistance. The extra resistance could be on the supply side or the return side of the circuit. All the voltage drops in the circuit will add up to the total supply voltage delivered to the circuit. I hope that this isnât confusing you more.
Not finding any headlight relays in any info I have. I do find a DRL relay. Doesnât list any headlight relay in fuse block info or reference in any wiring info.
what model year?
how many sealed beams per side?
Fire Truck:
2008 Chev. C5500 4 dr. Duramax Diesel
Kodiak Model CC5E044
1 headlight per side.
Ambulance (Which I havenât tested or did anything with yet)
2008 Chev. C5500 2 Dr. Duramax Diesel
Kodiak Model CC4C044
2 Headlight per side.
I just looked at the wiring diagrams
Low beam goes through the drl relay . . . high beam bypasses the relay
What I just said applies for both trucks
you want to look at pages D-221, D-222 and D-228
I believe that by backprobing, you should be able to determine where youâre losing that voltage
If I were you, Iâd use that diagram and your meter to make sure you actually have 14V at idle coming out of the switch, going into the relay, then coming out of the relay
you can pretty much ignore anything on the schematic that says âhighâ . . . as you have no problem with the high beams, correct?
in my opinion, you may need to concentrate on circuit 12
High beams are low voltage/dim also. They are not so noticeable as the truck came with the round aux driving lights wired to come on when you turn on the high beams on dimmer switch.
Still, if aux drive lights would quit/burn out or whatever, the high beams would be really dim by themselves as things are now.
I have the other center LED light bar wired separately with direct power from battery and a interior remote to turn them on/off or flash. That center LED light bar is not near as bright as the round HID lights but way brighter than the factory headlights by themselves on high beam.
I have not traced the wiring to see how the round drive lights are wired and how the dimmer switch turns them on. Assuming they are direct wired from battery and have a solenoid connected to headlight bright power wire somewhere to activate.
That is why the âlow powerâ dim lights are so noticeable. Go from really bright HID to really dim low beam.
Looking at the data that was nicely provided by @db4690 I was surprised to see that the high beam circuit does not have a relay in the circuit. You stated that the voltage at the switch was okay but the voltage at the lights is slightly low (11.7v). Was that reading for the DRL lights or the high beams? If that reading was for the highs then I would say that is due to wire losses and you would need to bypass the old wiring to improve the lighting output.
The data didnât show how the DRL lights are dimmed. I assume through a resistor.
You all have been a big help. Especially @db4690 who provided the link to GM wiring. I have ordered aux. solenoids and am going to run new power to the headlights. I donât think that will completely fix the issue as a lot of what I have read talks about a design problem. But getting 14 volts to the lights sure seems to brighten them up.
Thanks all!
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Good luck, and please let us know how it works out
I just thought of something new . . . those additional lights in the pictures . . . how are they wired up?
Do they turn on with the headlight switch, or are you running a completely separate circuit?
By the way . . . Iâm not sure what this âdesign problemâ is youâre referring to. We have lots of Kodiaks and Topkicks in our fleet, of various model years, and we donât have any problems with low voltage to the sealed beams
For the record, Iâm on the west coast and thereâs no rust to speak of. Iâm not sure where youâre at, maybe the wiring is corroded and canât carry the full load?
Have you looked into performing voltage drop tests of the wiring associated with the headlight switch, drl relays and so forth?
I addressed all your questions in my previous post. Design issue I read about was the way the headlights were set back in the hood assembly. Not sure what that would do but another truck (Kenworth) we have is set back same way and its headlights are not that bright either so it does make sense that could be issue. Plus increasing to 14 volts still doesnât make the Kodiak headlights all that great either. I installed LED bulbs in Kenworth but I havenât driven it at night yet to check if that helped. Havenât checked voltage on that one either. Location is South Dakota but trucks are kept inside and washed regularly. No rust issues. The green Kodiak we just bought. It came with driving lights already installed so last owner (BLM in Montana) must have had same issues. Ambulance is Federal Surplus from Navy Base but not sure where. Both are good trucks with no rust with only issues being headlights.