Any help for dim headlights?

[richard5933]

I may be full of sh*t on the 12 volt option. Those resistors may be for daytime running lights running at reduced brightness. Do you have them? When I get a chance, I'll check the wiring diagrams to determine one way or the other.

Best I can tell, the daytime running lamps only work when the engine is running. There is a tap from one of the generator terminals which has 12v output. It goes to the low-beam terminal on the dimmer switch, but through a diode. The diode prevents the 24v of the headlight circuit from back feeding to the 12v terminal on the generator when the headlights are turned off.

Seems like they ran the 12v to the headlights to provide half-power to them for daytime use. I'm going to have to confirm this, but my guess is that the resistor panel is in the circuit immediately behind the headlights themselves. They serve to cut the 24v input from the bus in half so that 12v headlamps can be used. When the daytime running lamp circuit is providing the 12v input, the resistor panel cuts it in half which provides 6 volts to the 12v headlights.

My guess is that if I replace the resistor panel with modern 24v-12v reducer(s), the daytime running lights won't function. I'm debating whether to install one large 24v-12v reducer upstream from the headlight switch, or keep the wiring basically the same as it is now but replace the resistor bank with four individual 24v-12v reducers (left low, right low, left high, & right high). Either way, the modern 24v-12v reducers are designed to provide a steady output, usually something around 13.8v, when there is an input of 20-30v. With the 12v input from the DRL circuit they would do nothing.

I'm heading out to the bus to do some more inspecting and voltage checks. Will report back with what I find.

[richard5933]

Spent a few hours checking voltage and running through the circuits checking for problems. Here is what I found:

Circuit design: The flow goes as follows...
30a 24v Breaker > Headlight Switch > Dimmer Switch > Circuit breaker > Resistor Panel > 12v to Low Beams
                                                                                > Circuit breaker > Resister Paenl > 12v to High Beams

Resistor panel:
There are six pairs of resistors. The panel has four input/output conductors.: two for low beam and two for high beam on both input & output. I took apart the panel so I could test each resistor pair, they are all labeled with their resistance, and each tested spot on.

Voltage Drop
There was about a 1.5v voltage drop from the start of the circuit to where the power entered the resistor panels when I started today. After cleaning, tightening, and using DeOxit to remove oxidation I got that down to about 0.4v voltage drop. Still not perfect, but better.

At the end of the day, I was able to get the voltage being output to the headlights from 9.8v up to about 11.5v. Still not where it needs to be, but certainly a great deal better. The headlights have gone from being virtually useless and downright dangerous to just weak and not up to snuff.

Plan moving forward:
I like having 12v headlights. This gives me many more options for replacement bulbs and future upgrades. There is just so much better availability in the 12v headlight world.

That said, I'm going to spend some time this winter investigating options for replacing the resister panel with a more modern 24v-to-12v voltage converter method. i like that they used four separate circuits to feed the headlights - if the resistors in one leg fail I'd be left with three working headlights. A failure in this setup isn't catastrophic. I'd like to go with the factory setup and wiring for now, but with replacing the resistors with something like this:

https://www.donrowe.com/Samlex-SDC-15-DC-DC-Converter-p/sdc-15.htm

four of these would be fed from the same four circuits that currently feed the resister panel. Then I'd upgrade the 16 ga wire from the output of the converters to the headlights to 12 ga wire to avoid any loss after the converter. These convertors will output a consistent 13.8v to the headlights with an input from 20-30v.

I could also use one much larger 24v-to-12v converter to supply the 12v to the system much higher up in the circuit, probably after the initial 30a circuit breaker. However, by putting the converters just before the headlights in the circuit, any voltage loss would be minimized since they will output 13.8v even with a slight decrease in their input.

[eagle19952]

i would still check ohms/resistance of individual wires, if you have not already.

[buswarrior]

dimmer switch leads a nasty life, my bet is it is good for some losses.

adding some modern relays and getting the amperage to run the lights out of the switch and dimmer will also help the cause.

happy coaching!
buswarrior

[richard5933]

i would still check ohms/resistance of individual wires, if you have not already.

Done - wires and connectors are pretty good. I cleaned up the ones I found with issues using DeOxit

dimmer switch leads a nasty life, my bet is it is good for some losses.

adding some modern relays and getting the amperage to run the lights out of the switch and dimmer will also help the cause.

happy coaching!
buswarrior

Still wearing its wax/rubber coating underneath. Didn't find any noticeable voltage drop across it.

I'm still thinking the big problem is the resistor panel just not having a steady and reliable output. By switching to a more modern electronic converter, I'll have consistent 13.8v output to the headlights with an input of 20v-30v.

[eagle19952]

I'm still thinking the big problem is the resistor panel just not having a steady and reliable output.

Resistors, look easy to change, are cheap.
Why couldn't you get a guru to calculate the voltage you want ? and replace them ?
A head lamp will survive 14v and be just that much brighter.
And the lamps are almost free if they last a little shorter life.

[chessie4905]

Resistors of that size aren't going to be cheap.

[bevans6]

Resistors also throw away power, just waste it in heat.  Maybe power is free when the bus is running, but still...

[luvrbus]

I would be for tossing the resistors and do the upgrading,they waste power and drop voltage the longer they are in use under power,years back when Ford used resistors in the heating and AC units you could hear the fan slowing down after running a while.Resistors in a head lamp system makes no sense interesting. I think the MCI center tap from 24v to 12 v would be better than that and I don't care for the center tap much     

[eagle19952]

resistors,, well they seem to have worked well for 40 years...
nothing lasts forever.
converters don't either.

[luvrbus]

resistors,, well they seem to have worked well for 40 years...
nothing lasts forever.
converters don't either.

Lol I doubt they were 100% effective for 40 years with that type draw from the headlamps 

[Lee Bradley]

Resistors could be prefect but don't match today's headlights. The system is setup for the resistor resistance to match the headlight resistance so you have the same voltage drop across the resistor and the headlight. If the modern headlights are more efficient, then they probably have less draw and you get more drop across the resistor and less voltage at the headlight.

[richard5933]

The Samlex 24v-12v converters are nice, but they are large and pricey.

Since the headlights are divided into four separate legs and each leg doesn't carry that high a current, I'm thinking about using four of these: https://www.amazon.com/dp/B01LY8D7U0/?coliid=IZCHLZO0I1H6W&colid=1K5E0RD2YQ7ZJ&psc=0&ref_=lv_ov_lig_dp_it

Not that fond of using imported electronics, but I'd be using these at far less than their rated current limit.

Anyone have experience with something similar? Or maybe someone has a better suggestion for a converter?

[chessie4905]

I just installed this one for my King Cruise Control, electric sunvisors,  cigarette style socket, and pulse air wiper control. Nice unit and has a flat fuse on it for protection.

https://www.amazon.com/Power-Step-Down-Converter-Technology/dp/B003P17X8I?ref=silk_at_search

[eagle19952]

I just installed this one for my King Cruise Control, electric sunvisors,  cigarette style socket, and pulse air wiper control. Nice unit and has a flat fuse on it for protection.

https://www.amazon.com/Power-Step-Down-Converter-Technology/dp/B003P17X8I?ref=silk_at_search

PYLE has been known to make good stuff