96 taco only high beams no low beam

Following up. I replaced the headlight dimmer with a brand new OEM part, plus double checked wires and connections. It is still not working, which is discouraging to me. Same symptom: no low beams, hi beam indicator light on when lights are in low beam mode, high beams work fine.

Any other ideas?

 

I assume that you say, high beam indicator is on when you are either on low or high beam, correct?

I think it's time to get a meter and start tracing where the continuity is broken. There are not many places it can be. It is just that area marked in yellow box from my original image showing electrical diagram.








Note: I do not have 1996 diagram and the diagram below shows contact numbers of 1999, In my 1995 the contact 17 at the dimmer switch in 1999 diagram is the number 3 in 1995 diagram. So maybe in your truck it is contact number 3, below I will call it 17 .

To explain where are the components:

The contact 17 at combination switch is a plug where you had to replace the the wire coming of the switch. Make sure the mating contact is fine. Measure the voltage at that contact when you turn the low beam on. It should be zero volt. An should show 12V when switch is on high beam. If you use a probe (like a bulb) it should show continuity to the ground at low beam position.

Contacts 14-1A, 17-1C and 13-1F are located at JB1 - which is the big junction box under the left side of the dash (the same where you have some fuses at the front, relays, flasher, and the unit with the buzzer for the open door). This one is SOB to get to, as all of these plugs (1A, 1C ad 1F) are on the back of the box (facing the firewall). I don't have a diagram for 1996 but I think it will match my 1995.



13-1F is going to your headlights low beam filament. I think it is OK because it powers your high beam indicator via the contact 17-1C. With symptoms you are reporting I would expect that both wires will show 12V at high beam and low beam. Of course if everything works correctly that contact should show 12V at high beam and 0V at low beam.

The issue might be at 14-1A - that wire goes to to a dimmer switch (headlight selector switch). The switch is grounding that point when low beam is selected. If that contact shows 12V at high beam and low beam than the problem is probably between JB1 and the dimmer switch switch (broken wire possibly???). In this case you may double verify it by setting the dimmer switch to low beam and then short that contact to the ground you should see low beam lighting up and high beam indicator going off. If this is the case use a piece of wire and connect that contact with contact 17 at the dimmer switch. If lights work OK, that it means this is the problem.

If you see 12V at high beam and 0V at low beam in this contact than examine the plug and contact if it is not burned (or overheated). If it is OK that JB1 is missing the internal connection (that would be the first time ever I heard that). If this is a case you can fix it without replacing the entire JB1 (expensive) by bypassing JB1 and having a piece of wire connecting 13-1F with 14-1A. Just make sure that wire can handle low beam current from bot bulbs (at least 10A constantly and 30A short time).

 

An excellent description and I'll start testing continuity ASAP. Thank you for your help @RysiuM! And yes, I meant high beam indicator is on when I'm either on low or high beam (in addition to low beam not working at all).

 

your intitial description is very hard to understand thoroughly, but this here can't be unless you have a short to ground. One of those three wires has to be ground.

 

I take that back. That's very different from most headlights I've wired. Looks like two switched 0VDC and a constant fused 12VDC. Perhaps R-G is an open wire between J9A and C14. If the multifunction switch is good and grounded then this is all that's left. A wire can be open and you won't know because it has separated inside the jacket. Usually happens where there's a lot of stress or movement like near a plug or where it goes around a corner.

Good luck.

If the diagram is right and R-G takes it to ground I would unplug jumper connector J9/J10 and use a length of wire to ground and put the other end of it to the R-G wire heading to one of the headlights and see if a low beam turns on.

 

Is that highlighted box representing a relay or a junction of three wires? It makes sense if it's a relay although I don't see the coil side of it.

Sorry, I love troubleshooting so I'm sticking my nose in too.

 

I Highlighted with yellow box the troubleshooting area. It is a part of JB1 (three connectors), the wire between JB1 and dimmer switch, and the connector at dimmer switch (17).

 

bear with me, but what stops that hi beam indicator from lighting on the low beam if those three wires are terminated together? There must be something that opens the circuit going to the indicator. Why am I not seeing it? Why have it in the low beam circuit??

 

If that grey box depicted a relay and the indicator was on a NC contact it would make sense that if the low beam circuit wasn't on the indicator would lite. Still seems kinda over complicated that way.

 

When the low beams are on the R-G wire is pulled to ground through the headlight switch. As a result the high beam indicator has a ground on both terminals and can't light. When the high beams are on the R-Y wire is grounded but there is power on the R-G wire all the way to the headlight switch (but not through it to ground) provided through the low beam headlights. The high beam indicator lights, but draws so little power that the small current will not light the low beam headlights. If both low beams are out the high beams will still work but the high beam indicator will not light. (ask me how I know -- LOL)

This powered headlight common terminal grounding headlight switch setup is pretty common in newer vehicles. It allows each headlight to have its own fuse early in the headlight circuit.

 

This is super easy to fix, you don't need the schematics at all. You lost a ground somewhere in the system. You'll never find it.
The fix is this.
Unplug one headlight, doesn't matter which one.
Find the negative (ground) wire off the headlight plug, There are three wires, one is ground.
Run a wire from that plug to a ground on the truck, NOT to the battery, just find a body screw and attach the wire to that.

Now, your brights and dims will work, but you will notice you no longer have the high beam indicator on the dash. You just have to be aware when driving at night, and you can prolly tell when the brights are on anyway. Good luck.

 

Now I see it. Thanks for taking the time to straighten me out.

 

Interesting, thank you @Deathbysnusnu . I could live with this. Now I wonder which headlight prong / plug is the negative one on my 1996...

 

I don't have mine to check anymore, but pretty sure it was the center terminal.

 

What is the bulb number

 

Google-
"The pinouts for H6054 headlight bulbs are:

• UP: Low beam+
• LEFT: High beam+
• RIGHT: Ground-

Some vehicles, like Toyotas, may have different pinouts than factory-shipped lamps. " (of course)

 

I am not following. Tacoma (US version, not Canadian with DRL) has the circuit up side down, different from any other car. The bulb is powered 12V from common (via the relay energized by either low or high beam switch) and low or high filament pulled to a ground by hi/lo beam selector switch. The problem here is that lo beam filament is not pulled down to ground. You can't just hardwire it to a ground because at hi beam both filaments will be powered and bulb will melt down very fast ( or you will blow the relay or the fuse). Or am I missing something?

 

I'll second that. Seems like that low beam will also be on constantly if that was done.

Just find the bad wire. It's not all that hard. Sure beats bleeding brakes or changing a ball joint!

I hope the OP updates us when he gets it fingered out. I'd like to see what it was...

 

I described how to fix it. I did this to my '96 over 20 years ago and it was just fine, no both filaments don't light up like you think.
There is more than one thread on this site regarding this issue, I have replied to a few of them and it works when they try it.
I can't explain why it works, because I don't know. i was told to do this by a mechanic after doing the exact same things you guys are doing and having no luck.
So either try it, it just might work, or spend the rest of the time you own the truck trying to trace it down.

 

I did look over threads about this fix @Deathbysnusnu and even saw an image of your wiring fix. I'll poke around the truck a bit more this weekend once the weather clears up here in Northern California and let everyone know how things work out. I VERY much appreciate everyone's help!