Low beams don't work, high beams do,

I have a 2002 Tacoma Pre-Runner. Low beams are not working and the high beam indicator is lit which is odd. The high beams work. This started earlier this week and the first day or 2, sometimes the lights would work but now not at all. I installed new fuses, relay and headlights but none of that worked. Also, will add that when I switch light on and switch from low beam to high beam I do hear clicking in the fuse box which I guess is the relay. Don't know if there is any relation but two weeks ago there was a faint smell of like something electrical burning, but I couldn't figure out what was going on. Does anyone have any idea what the problem could be?

 

Burning electrical could be a LOT of things.
Start by checking the relays for the headlights under the hood. I've seen them lock up before, and they're a pretty cheap fix.

 

I replaced the relay.

 

That "smells" like a grounding issue. IIRC these lights are ground switched, which means the switch completes the ground, not the pos(+) wire.

Bet you have a shorted out ground somewhere.

 

Did you check to see if they're getting power?

 

I am pretty ignorant so I am not sure how I am supposed to check that or where. Usually I can watch a video and fix almost anything but I am not finding a video for this. So how do I check the grounding issue? I assume I'd use the meter but where would I connect?

 

Oh man, electrical issues, especially grounding is one of those things that even electricians hate. It's like chasing ghosts.

First step is to find a wiring diagram (a good google search will find what you need, or if you have a factory service manual) for the lights and do what you can to try and understand the wiring. It can be like trying to read Greek, but you'll get it eventually.

You can check if something is grounded by simply taking your voltmeter and checking for continuity between a known ground (the neg battery terminal, frame, etc...) and the particular plug you're testing. The hard part is always figuring out which plug you're supposed to be looking at.

The other thing is to just inspect visually. You're likely going to have to take a bunch of stuff part to try and see every inch of wire from the switch to the lights.

With electrical problems, you just have to be methodical. Start at one end of the circuit and work your way to the end.

 

Thanks! I figured once I replaced stuff and the lights still didn't work, I'd have some exploring to do.

 

I would tend to rule out things with moving parts, first. Like the switch.

The switches can go bad, too. So you gotta figure out the cost-benefit of trying to track down a ghost vs. just replacing a bunch of parts.

For $30 this might be worth a shot...
https://www.carparts.com/details/To..._UDgBXo6LZQYFFxIRZkaApxREALw_wcB&gclsrc=aw.ds

 

If Low beam is not working (or creating "electrical burn" smell) and high beam is working I would suspect the switch itself or connector at that switch. It sucks but full current that is going via both headlight bulbs (total around 8-10A) is going through that poor switch and with age contacts are getting worse and worse. Increased resistance of contact will make them hotter and that degrades them even more.

By the way headlight relay clicking is running on different contacts in the light switch, and it is lo current contact. The ground is common from both low and high beam so if high beam is working, then you don't have problem with ground. It is most likely a switch itself. Especially when you see high beam light indicator on - meaning there is a continuity between the low beam filament and the switch connector.

By the way do you have DRL option in your truck or not? DRL equipped trucks have much more complicated headlight circuit than non-DRL. In my comments above I was thinking of non-DRL truck.

 

Threads like this come up every few months. Do a search. Someone in a headlight thread a few months ago posted the headlight circuit wiring diagram.

The high beam indicator receives power through the low beam filaments. Sounds odd but you'd have to look at the wiring digram to understand. Anyway this means the bulbs are good. It sounds more like the headlight switch or related wiring.

Every part can be easily tested with a multimeter by understanding the wiring diagram. Absolutely no need to throw parts at it!

 

I just put the meter to the headlights. One of the ports registered 276.5. The other 2 ports were about 11.5. I call them ports as the only name I could think of. On low beams it was normal 12.3. I'm not a mechanic or electrician but that seems pretty whacked. Anyone know what that could be?

 

Measuring the voltage at the bulb socket will not give you much information. Looking at the socket that goes to your headlight should be like this:




Remove both bulbs (left and right) from their sockets and measure the voltage at one of them.

1. With headlights switch in OFF position, and Low beam is selected you should have:
0V (low resistance) on Low Beam,
Open circuit on High Beam,
Open circuit on +12V Common

2. With headlights switch in OFF position, and High beam is selected you should have:
0V (high resistance) on Low Beam,
0V (low resistance) on High Beam,
Open circuit on +12V Common

3. With headlights switch in ON position, and Low beam is selected you should have:
0V (low resistance) on Low Beam,
Open circuit on High Beam
12V on +12V Common

4. With headlights switch in OFF position, and High beam is selected you should have:
0V (high resistance) on Low Beam,
0V (low resistance) on High Beam,
12V on +12V Common

My take is if the switch is bad then you have 0V (high resistance) on Low Beam contact, regardless of light selection switch position.

That high resistance is because Low Beam contact is connected to you high beam indicator lamp on the dashboard - that is 5W bulb, so a multimeter will show continuity to ground, but the resistance will be around 20ohm or so.

 

I think I found where the electrical burning smell came from. I took out the turn signal/headlight switch from the steering column. From the wires, one of the plug in things is all black. On the switch itself, where it would plug in, the prong is all black and there's a bit of melting in the plastic around the prong. My question then is the switch bad or is there a problem in the wiring? How do I figure that out?

 

Well I found the burning wire smell. If you look at the plug, it's kind of melted and broken too. Should I replace that? By looking at it, is the switch bad or do I have a wiring problem somewhere? In other words, if I replace the switch, will that solve the problem? I can figure stuff out but I am bad clueless.

 

Damn, that would do it! You'll really want to replace that plug too.

Hard to know if that was the cause or the symptom of your issue, though.

 

I told you


You have to replace not only the switch but also that connector too. That burned contact (number 17) is the contact to ground low beam. This is why I hate Toyota's idea to run full current from both headlights through the switch at steering column. Lazy design. With age the contact will go bad and as soon as the resistance increases it will go downhill very fast.

So contacts 17 at the switch and the plug are FUBAR. What I will do:

1. Get a new switch (new or from donor truck)
2. Get the connector cut from donor truck with a couple of inches wires attached.
3. Remove all wires with contacts from the donor plug except wire 17 (the one you have burned contact)
4. Remove all wires with contacts from your plug. Cut off the burned contact (may not be able to remove it from the plug)
5. Put all wires with contacts from your truck to new empty plug
5. But connect wire from contact 17 from your truck with wire from contact 17 in the new plug.

Note regarding 2: you can get both pigtail and plug's body from Toyota dealer but probably waiting for special order.

In other words you will reuse all contacts and wires from your truck except burned contact 17 and just replace contact 17 (pigtail) and plug's body.

For the future:
Do not run high wattage bulbs in headlights unless you have add-on harness. Make sure the headlight fuses are 10A (not more). Never connect un-fused power to the headlight plug (for testing for example). It is very easy to f-ck up the truck electrical if you don't know what you are doing.

 

That connector can be found on a few different Toyota and Lexus models from that era so don't feel limited to only Tacomas at the junkyard. I think mine came from a Camry or something like that. For reference the actual female connector part number is 90980-11672 but good luck finding one for sale. This is an ongoing problem stemming from a poor design.

 

You could just take the two wires that meet at the burned terminal and connect them outside of the connector. I realize the best way is to replace the connector, but in a pinch if you needed to get it working before you can find another connector this would work.

 

Another reason the "proper headlight upgrade" is so great.

It takes the full voltage out of the equation, and runs the lights direct from the battery with relays. Even with the same lights, they get brighter because the voltage actually increases because of the direct connection.