05 Tacoma keeps eating Low Beams. Diagnosis Help

I'm going to be working on a friends 05 Tacoma. The truck is having a problem with only the driver's side headlight. It has always had trouble with eating bulbs, but the last bulb lasted a month and is becoming expensive to replace a headlight every month. Here's what I'm planning on checking, feel free to tell me your thoughts on it or what else I should check.

1) Check for Corrosion on the bulb/at wiring harness

2) Check the voltage at the harness. See if there are spikes in voltage (checking to see if the alternator has a faulty Voltage Regulator).

3) Check grounds at the headlight

4) Check for corrosion at the Relay and or Fuse

Anything else?

 

Check the headlight mounting to determine if unwanted vibration or movement is present. Had a tail light on an old truck that always burned out due to the light assembly shaking really badly, and couldn't figure it out with the truck sitting still. It vibrated the bulb to the point it broke the filament.

 

Good point. Thank you for pointing that out.

 

What brand of lamps are you putting in? Look on the back of the package, it will have an estimated amount of hours that they are supposed to last. The cheapest ones have over 1000hrs of life, where as the fancier brighter ones have only about 120hrs of life.

 

The truck uses the el cheapo Sylvanias. Don't remember what they call them. But its the Walmart special cheap headlights

 

Ok, another thing is contamination. Moisture, oil, dirt, pretty much anything. The seal is important because of ambient humidity can have an effect on this. Also wear nitrile gloves to install to avoid oily fingers from contacting the lamp.

 

Check current draw on each harness at the connector. They should be the same. If not, corrosion might be the cause of higher draw. Can’t figure out why that would cause bulb failure though.

 

Thanks for the tip. I replaced the last headlight an wore gloves when I put it in. Sadly its still blowing.

 

I can't either, but I have heard that when corrosion and headlights mix blown headlights can be a result.

 

Some contact cleaner may help on the harness if there is corrosion.

 

If I get in there tomorrow and see corrosion I'm just gonna solder in a new harness.

 

Good idea.

 

Clean off the flux, it's acid used to clean the wire to accept the solder. If you can find the shrink tubing with the adhesive inside, that'll seal the solder joint for almost ever.

 

Are you using electrical grease when installing the new lights? I had a couple of bulbs go out pretty quick on me without the grease. I used it on the next set and the current set has lasted a couple of years so far.

 

It blows the headlight because corrosion is added resistance to the circuit. This added resistance is lowering the available voltage to the headlight.
The headlight is 55 watts low beam let's say, and the normal voltage to the lamp is 13.5 volts. That lamp is using just over 4 amps of current.
Going overboard to illustrate the point, the corrosion is so bad, that there's only 10 volts available to the light. The light still wants to produce 55 watts of light, but now it draws 5.5 amps of current. That current is to much for the filament to carry, and blows open.

 

its a resistive load and lower voltage will mean lower current

AC motors on the other hand will draw more current with less volts

 

+1 I found this out the hard way after replacing bulbs every couple months. After a WTF rant moment at the local AutoZone, the guy offered me some light bulb education. Those bulbs are a bitch to replace with that stupid tension spring/rubber boot pretzel contraption. HATE THOSE F'NG LIGHT BULBS!

 

Corrosion would cause a higher resistance... and lower current.

E = I X R

I = E / R

R = E / I

 

The corrosion is a resistance in series with the lamp and will therefore have a voltage drop across it.
Don't compare ac and dc. Especially motors... Inductance, phase shift, power factor all contribute variables that aren't present with dc.

 

You cannot increase the resistance and also increase the current. Not possible. Watts is not a measurement of light, but expended energy.

I agree with what you are saying with the exception of the power rating of the installed lamps. The added resistance will not cause any increase in current due to the voltage loss at the corroded connection. Power in watts is developed from the voltage multiplied by the current. P = I x E.

Good link. Plug in some numbers:

http://www.ohmslawcalculator.com/ohms-law-calculator