Speedometer/Tachometer Dash Lights Not Working. Which Fuse?

I finally got the right wiring harness for installing a new head unit in my wife's 2006 DCSB and she is stoked to finally have Bluetooth connectivity.

However, while floundering with the wrong harness, I popped a fuse (the 7.5A "GAUGE" fuse under the dash). After replacing that, all the of the interior electronics work (gauges, clock, heater lights, heater, windows, dash lights, dome lights and stereo) but the lights for the speedo and tach don't come on when the headlights are turned on. I've pulled all the obvious fuses, visually inspected them and all appear unbroken. I also checked the dial rheostat to see if it got turned off but turning the little wheel has no effect.

Anyone know which fuse the speedo/tach light circuit is on to help me narrow down the hunt? I'll check continuity if necessary, but always nice when TW helps me cut to the chase.

Thanks!

 

After searching some other forums (Toyota Nation), it turns out this is pretty common when replacing the Head Unit and either mixing up some of the grounding which leads to frying the rheostat. I'm guessing I did that with the non-working harness. Bummer it's a $120 from Toyota (PN 84119-04020). I'll try to find a used one and hope that the correct Metra harness I got won't fry it again. Cheers!

 

If that indeed is the problem, try taking it to a tv/stereo repair shop. There's no way that part should cost $120, it has a $2 rheostat in it. Without cracking it open to see what's inside, not really possible to see what needs to be replaced.

Hopefully you have a shop like that in your area haha. I have 1 guy, he's fixed loads of car stuff for me. Tv, stereo, xbox, car parts... it's all the same lol.

 

This is the insides of a Rav4 rheostat. I didn’t try to pry that white plastic knob off. Someone that’s into electronics might be able to source this. I measured the resistance and it’s 10K ohms. The whole thing is different looking on the outside than the Taco rheostat, so not sure if the insides are the same.

 

Eh, it's been a while. Is that a rheo or a potentiometer? I think it's a pot? If you're getting 10k off of it, then I would just assume it's supposed to be 10k because that's pretty standard. Which could be good, since that's not the blown bits. If it shorted, then something arc'd over and killed a trace I would guess. I mean, it would come down to taking what you have apart and you could just ohm out the traces and see where it broke, if that's how it did break.

I have no idea what the pinout on the back is, but 2 (I'm assuming the ones you ohm'd out) will be constant (10k) and the 3'rd would be the swiper.

If the gauges die with the headlights on, man.. I'm really stretching on guesses here without knowing anything about the guts of it.... maybe it's just the LED shorted to ground is all.

 

There's a complete used one on Ebay for $27 shipped. Not terrible. But if I can source a cheap rheostat and resolder it in the old housing, it'll be a lesson learned for pennies on the dollar. Thanks for the pics Muddinfun. I'll pull her dimmer and see if I can pry it open without too much drama.

 

This is the assumption I made and how I measured it. I do know from past reading that there's something goofy about how the dimmer works. That's all I know. Also, that sliding switch you see in there does something.

 

Sorry for the double post, I always think to clarify my own thoughts after the fact... So, you popped a fuse, which means something shorted. Since you're still seeing 10k, I would imagine the resistor bits are fine. If it only happens when the headlights are on, I would suspect/guess the LED is shorting to ground. Again, kinda hard to make guesses without seeing anything. You found the 10k pins, you would have to crack it open, and ohm out the traces to see what shouldn't be going to ground. Again, I would suspect that the LED is toast, could *could* just desolder/cut it out, and effectively turn the ground short to an open short, and the gauges would work. Your light on the dimmer won't though. You would have to find where it shorted inside of the switch (if at all, could just literally be the LED) and then desolder and replace the led. Again... this is all real vague guesses on my part here.

 

There was mention in the threads I read about a bad ground behind the kick panel. I didn't mess with anything there so not sure if this applies to my issue. Can you give me something more to look for there? Likely not enough amps to have fried the ground wire, right?

 

Use a knife to carefully pry the sides of the face away from the tabs and the face comes off. The face has to come off 1st. Then carefully pry the sides to pop the white plastic part out.

 

Great info. I know just enough 12v to get in trouble and not much more. I may just bypass the rheostat and hardwire the internals as wifey says she never uses the dimmer. That kinda fix plays havoc on my OCD, though.

 

I would just dead reckon that wouldn't be the issue. Just based on it working fine until you turn the headlights on, there has to be something small I would imagine that is shorting out, but not enough to trip a 7.5A fuse. I wish I had something with pinouts, because if the switch was taken out of the equation it would be easy to tell that is the culprit and not a ground somewhere else.

 

You posted right before my second logic haha. Yeah, if you know how to bypass the entire switch, that's also an option.

Edit: Diagnostic option IMO, clearly doesn't *resolve* the issue because you don't have a switch anymore. But would identify the culprit.

 

No it all works with the exception of the instrument lights (they don't work at all). So my best (semi-educated) guess is that I fried the rheostat with my wiring SNAFU

 

Ohhhh.... I read that really wrong.... shit lol. I thought it was killing the speedo and tach when the lights were on, not the lights on the speedo and tach. The rest of the instrument cluster lights work though?

 

Yes that's correct. Instrument lights just plain don't work but everything else does.

 

Fuck me, I can't read. I thought it was kinda goofy that a small short would cause that kind of problem, but... it's not totally unreasonable to assume. Anyways... If the other lights work, makes it easy. You killed bulbs/leds. All of those are going to be on the same circuit for sure. If the temp/gas etc light up, that isolates it down to a cluster issue, if all the bulbs run on the same circuit, which I'm sure they do, narrows it down to a bulb issue, it can only fail open or closed, again... if the other lights work, it has to have failed open == blown bulbs.

 

Just went and pulled the dimmer switch. Here's the internals (with no obvious signs of heat, shorting, etc). There are 5 pins. How can I check functionality and/or continuity of this dimmer to isolate it to the bulbs? I've got a voltmeter and know how to use about 10% of it, so I won't be offended if you tell me what to do like you would a 5 year old.

 

That makes sense. Except....was re-reading some of the posts I read this morning with the information you guys imparted on me here. Turns out, if the dimmer switch is unplugged from the dash light circuit, it bypasses it and the instrument lights should work. I ran out to the truck to confirm. YES! All the dash lights work! So...I gotta conclude that shorting the 7.5A GAUGE fuse also damaged some component of the dimmer switch assembly.

Now to figure out which part and see if I can replace it.... or just say F it and order the $27 used part.

 

WOW! That’s a lot different than the Rav4 dimmer.

So, based on your test results, it would appear that the dimmer is shunting the voltage to ground to dim the LEDs. That aluminum heat sink is obviously to dissipate the heat. I would bet that a local TV repair guy could take a few readings with his multimeter and tell you exactly whats wrong.