05 9400i Daytime Running Lights + LEDs

https://www.amazon.ca/Nokya-NOK9595-Hyper-Flash-Resistor/dp/B00AWQ1OC0
On my Western Star when I installed Speaker LED headlights, the daytime lights would flash really fast. I installed these resistors and it solved my problem. Your truck probably does not detect enough of a load, so it just gives up.
I found all I had to do was install two of these in series, one end to ground the other end just to one of the headlight relays was enough to do the trick. At first I installed one each to each relay, but the heat these things put out is quite severe, by putting two in series they ran just Luke warm.

 

I'm pretty sure the daytime running light module simply puts out about 8 volts to the headlights instead of regular battery voltage to get them a bit dimmer. LEDs will not light at all at such a low voltage and this is why they are not coming on. I recommend to wire your headlights to come on full when ever the key is on.