Bumping this dead thread after troubleshooting my high beams with no avail using the solutions here
What’s happening:
With the stock Toyota harness and a sealed beam, the High and Low beams function correctly
With a brand new Toyota H4 headlight harness, with a sealed beam plugged in, High and Low beams function correctly
With a brand new Toyota H4 Harness and the H4 light plugged in, only low beams function.
What I’ve done so far
- Cleaned the contacts within the wiring harness with sandpaper as described
- confirmed the connections to said contacts are in good shape
- confirmed turn signal stalk is tight
- confirmed the ground at the turn signal harness is functioning
What I haven’t done
1. take measurements with a multi meter: Next step, but I’m still confused why the high and low function would work in both harnesses on a sealed beam but not the H4 bulb
2. Replace the 02006’ headlight relay under the dash - the only part of the system I’ve yet to address to my knowledge
What else am I missing? Is there any other element of the stock wiring harness that I’m overlooking?
the fact that the sealed light High/Low beam works perfectly in both harness’s negates the issue with contacts /the turn signal harness in my mind - is this incorrect?
After some hardcore creeping I'm confident I found the solution which I can test, compliments of a 18 year old forum post on YODATECH - Posting it here so there's a record on MUD for some poor bastard like me in the future. My rationale was that the 1st Gen 4Runners have a compatible turn signal harness that guys often use, so one of them might have run into the issue - glad that hunch paid off.
Huge shout out to
@POTATO LAUNCHER for keeping me on the ball, and helping me troubleshoot on the fly today. Had you not kept telling me to dig I wouldn't have found this
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You have high resistance somewhere in the circuit, mostly likely the connector for the combination switch (light switch). I bet if you were to remove the connector to the switch, you will find a charred, partially melted connector pin.
When you turn the light switch on, you complete the connection to ground and that is what turns the lights on. If there is a point of high resistance in the ground circuit, the current will ground itself out through the high beam indicator.
The squall noise from the headlight relay is likely from the low voltage caused by the increased resistance. Much like a starter solenoid vibrates when you have a dead battery.
You can easily check this with a multimeter, or just pull the connector off the switch and check for burned connections.
If you have a multimeter, disconnect both connectors from BOTH headlights and check the following....
1) Find the red wire with a green stripe on the head light connector, this should have low resistance with ground when the headlights are in the low beam position. You should have less than about 1 ohm of resistance with ground. A typical charred contact will show about 5 ohms or more.
2) Find the Red wire with a yellow stripe on the head light connector. This should show low resistance with ground when the switch is in the high beam position, as described above.
Just remember to have both connectors disconnected from the headlights when you do this test to keep your meter from measuring the resistance in the filaments to ground. It will also keep your multimeter from measuring voltage when in ohms mode which can damage cheaper multimeters.
Symptoms: BOTH high beams do not work, High beam flash works AND low beams work.
Troubleshooting:
Turn headlights on. Make sure low beams come on.
Switch to high beam. Still no light, of course?
Find Pins 5 (Red-Yel Wire) and 13 (wht-blk) of dimmer combo switch . Jump 5 to 13. Got highs?
If you get high beam, it's bad contact between those 2 pins. You may be able to clean or fix. However, the flaw in headlight wiring of that generation where current flows on thin wire over a convoluted path (ask 4crawler) and though the dimmer-combo switch will shorten it's life again.
If you still don't get highs, jump pin 5 directly to shiny, bare metal ground. Got highs? If yes, it's bad connection between pin 13 and ground.
