HID Install Problem on the '99 Tahoe. HELP!

[JoyfulSoul]

Well, the HIDs worked so good on the LT low beam that I ordered a HID 5000K auto kit for the wife's '99 Tahoe. Unfortunately, it's a crap shoot whether both headlight HIDs will go on when the SUV starts up.

You see, the low beams are automatically turned on when the ignition key turns and starts the engine. My mechanic who installed the HID auto kit said to just quickly flick on the headlight switch or turn the car off and re-start the SUV quickly. He says that it could be the expensive light module or the light switch.

What do you electricians think would be the most economical fix? It's a 50/50 chance whether both headlights come on since its install.

[zippy_gg]

Larry, did you use a relay or relays in your installation?
How are you feeding your HID lights (electrically speaking)?

[Jerod521]

Here is what is probably going on. I believe GM uses something called Pulse Width Modulation (PWM) on some of their light circuits. What this does is rapidly switch the power on/off to achieve a certain power consumption or effect. IE daytime running lights using the same bulb. (Say your wanted a bulb that is designed for a 12v system to be dimmed. Instead of having to diff. fillaments in the bulb designed for diff. wattages, or using a resistor to lower the voltage, use the same fillament and change the % of time the bulb recieves the power. This may be confusing but here goes... PWM cycles the power hundereds of times a second. So, if you have a duty cycle of 70% it means the power is on 70% of the cycles during that time. Still a full 12volts. Just the effect of less.)


If GM is using PWM for your lights I would recommend using relays to trigger your HID's. Your HID's take a ton of power (only to start) and then runs at a lower wattage than halogens. This startup surge is what is probably giving you the intermittent nature of your light operation. If they don't use PWM this entire ramble was for nothing... sorry...

Also it could have something to do with how the light module monitors the bulbs. If this is the case I would still suggest using relays but try to match the resistance of your relay circuit with the resitance of your old halogen circuit, thus tricking the module into thinking the old bulb is still there.

To all I am sorry if this was confusing or jumbled, it is late, I am tired, and the 3 fingers of Knob Creek didn't help this much...