Tail lights don't light with headlight switch, dash dimmer doesn't work

Technical info on the Pontiac Vibe and Toyota Matrix including do-it-yourself info
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180 Out
Posts: 5
Joined: Fri Jun 12, 2009 5:11 am

Tail lights don't light with headlight switch, dash dimmer doesn't work

Post by 180 Out »

I am sharing this post because I searched and searched to find the fix for this problem and never found the answer. I first noticed the problem when, during daylight driving, the dash lights would dim and the dimmer switch would become active. Eventually I realized that the running lights -- tail lights and headlights -- were also turning on when this happened. No big deal, right? So I let it slide. But the next stage *was* a problem: that turning on the headlights, for night time driving, would not turn on the tail lights. Brake lights, turn signals, and 4-way flasher worked, but no running lights at the rear. Also, the dash lights dimmer switch had no effect.

The fix was (a) install new tail light bulbs, and (b) switch the tail light relay with the inverter relay. It is possible that switching the relays alone would have fixed the problem, but I had already swapped in the new bulbs, so I am leaving them in place. My theory is that the relay grew weak over time, while the resistance of the light bulbs grew stronger, such that the relay could no longer send enough amps to the bulbs to overcome their resistance. It's just a theory, and whatever the explanation, this two-step repair fixed the problem. Of course you could go to the Pick-n-Pull or O'Reilly's and get a new relay. But for $9 out the door for the new bulbs alone, this is a cheap fix.

These relays are located in the glove box area. First you need to drop the glove box, or remove it from its opening. There is a nub on each side that keeps the glove box from falling out of the dash. You push in on each side of the glove box, enough for the nub to clear the opening. You might also find it helpful to pop the telescoping strut loose from its pivot inside the dash. If you do this, the glove box will definitely be falling out of the dash. The relays are plugged into a panel at the top front of the dash opening. Here's a video on where to look: https://www.youtube.com/watch?v=QwujWnQwhck . The video guy says the tail light relay is the third one in the row of three black relays. This is wrong, at least with respect to my '03 Vibe. The tail light relay is the middle one. Although you can't see the row of relays, you can easily reach in and identify them and swap the middle one for the one on the end. Just grab them and wiggle them until they come loose. To reinstall, have the side of the relays with the part numbers printed on them facing toward you.

**EDIT: Please take a look at my second post, below**
Last edited by 180 Out on Sat Jul 17, 2021 7:34 am, edited 2 times in total.
Caretaker

Re: Tail lights don't light with headlight switch, dash dimmer doesn't work

Post by Caretaker »

thank you very much for sharing that. This is why I've been disappointed with the huge amounts of people who signed up to be members, yet never posted a single thing. Your one post could help many, many people; especially those who might do a generic internet search with the terms genvibe and headlight switch. Every Vibe and Matrix member here has likely run into an unusual problem that they have (or their mechanic has) solved. You will never know who your post will help, so as a long time member and one of the last standing, I thank you again.
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joatmon
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Location: SMC MD

Re: Tail lights don't light with headlight switch, dash dimmer doesn't work

Post by joatmon »

The three black relays are for the 12V outlet in the center console (between the seats), the tail lights, and the 110V AC inverter. The heater relay is the bigger blue one in this pic from my first '03. Some people have had the tail light relay work itself loose over time. Might be interesting to see if the 12V and 110V outlets still work after you swapped relays. And as Caretaker said, thanks for the post
P-relays.jpg
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180 Out
Posts: 5
Joined: Fri Jun 12, 2009 5:11 am

Re: Tail lights don't light with headlight switch, dash dimmer doesn't work

Post by 180 Out »

I am sorry to say that certain anomalous behaviors have returned to my tail light/dimmer switch functions. I am suspecting now that it is the Auto Light feature that is causing these problems, and that my installation of new tail light bulbs and my swapping of the tail light relay for the inverter relay is intermittently overriding the core malfunction. Time will tell. The most successful approach to any electrical problem is to troubleshoot from A to Z, using a test light, multimeter, wiring diagrams, and logic. What I am doing so far is the throw-parts-at-it approach, which sometimes is effective and sometimes is not; at least not until you stumble onto and replace the correct part.

BTW, the 110v inverter feature does still work, using the relay that was formerly the tail light relay. Both relays have the same part number printed on the side; they're the same relay. I expect the third relay, for the 12v Power Outlet, is also the same part number. I have not messed with this one, and the Power Outlet (aka cigarette lighter) still works as well.
jolt
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Joined: Sun Mar 02, 2014 2:07 am
Location: Twin Cities, Minnesota

Re: Tail lights don't light with headlight switch, dash dimmer doesn't work

Post by jolt »

If you have voltage at the tail lights, then grounding issue. If no voltage at lamp then power is not supplied and need to back track wiring to find where you are losing power at. Do you have voltage out of the light control switch? The headlamps and tail lamps have different output wires by my drawing for a Matrix. With no tail lamps, there should also be no license plate light too.
dougreed
Posts: 17
Joined: Mon Apr 12, 2010 12:40 am

Re: Tail lights don't light with headlight switch, dash dimmer doesn't work

Post by dougreed »

Sounds like a ground issue, but , it could be that in certain modes the electrons are finding ground at the wrong place in their journey. My 85 Saab had a similar issue. The cause was a short in the taillight fixture itself. Over the years heat had melted a small plastic tab and allowed 2 wire strips to touch. When the brakes were applied the lights went out, no brake applied, the lights worked!
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