JamesD

Not on Toyota's. The ground is fixed and the battery voltage is variable through the dimmer switch. Are we basically saying the same thing? I'am a little confused on your post.

James

4Crawler

iTrader: (3)

Not sure on the later models, but on my '85 the dimmer rheostat is definately on the grond side of the dimming lights:

http://www.4crawler.com/4x4/CheapTri...ne_Pix/26.html

JamesD

From what I'am looking at by the diagram you posted it doesn't use a the ground to adjust it uses battery voltage. If you don't believe me, get your test light see for yourself.

James

4Crawler

iTrader: (3)

The ground bus is at the bottom, the Rheostat is tied to ground, all the dimmable lights connect to the rheostat on one side and to power from the Tail Light fuse on the other side (top of diagram). The power side of the lights stays at 12 volts, the "ground" side of the lights varies from ~0 volts (full brightness) to ~12 volts (lights dimmed fully/off). When the "ground" voltage is above 0 volts the lights are dimmed.

So yes, the rheostat does drop the voltage across the lights, but it does so by raising the "ground" voltage the lights see, not by lowering the 12 volt side. So if you put a volt meter from the +12v side of the lights to ground, you will always measure 12 volts, regardless of the dimmer setting. Put the volt meter across one of those lights and it'll go from ~0 volts to ~12 volts depending on the dimmer setting.

Most other vehicles have the rheostat between the 12 volt source and the lights and thus the voltage across the light bulbs and from the light bulb to ground will varry from ~12 volts to ~0 volts depending on the dimmer setting and both measurements (across the bulb and bulb->ground) will be the same.

ETRNL

So hooking up the dimmer wire to the radio is possible but would take more than plugging in a wire?

ewong

yeah - hooking up the radio to the dimmer is very possible - I've done it..

The problem is that the after market devices (i.e the radio) use the same graound for the RADIO (i.e. the amp) as well as the light.

Since Toyota runs the rehostat ont he opposite side, to get a radido to "dim" you can do it two ways...

Build a voltage follower so that the current flows the opposite way (i.e. the way the radio light) wants it and power it on its own power supply...

OR

Open up the radio. Find the light. Assuming its an icadescent bulb.
Isolate the bulb on its OWN ground. Then wire that ground wire to the rehostat ground and run the radio's dimmer intput to fused and switched 12v (aka the ign 12v source of the radio).

4Crawler

iTrader: (3)

Ideally, you would want to get ahold of both wires feeding the backlight inside the device and run both out, one to the dimmer and one to the dash light power. Problem is many light bulbs are screwed into sockets that are grounded to the case of the device and that in turn is grounded either directly by the ground wire or my contact to the metal of the vehicle. Without a "floating" backlight (i.e. one that is not hard grounded) that one wire connection will not work. Basically that backlight will be wired around the dimmer to ground and thus cause all the other lights to run bright (and not be dimmable). So the best options for a switch, gauge or radio backlight is to either connect them to the switched power supply (light is on all the time) or to connect it to something like the parking light circuit so the backlight comes on with the vehicle lights. If the backlight is too bright, add a series resistor to the light circuit to do so. If you want a full dimming backlight, then, short of pulling out both wires, you would need some sort of buffer amp that "reads" the dimmed light voltage (across the dash light bulbs) and then feeds that same voltage (above ground) to the radio or switch backlight bulb.

ETRNL

wow... i think i will just leave the orange wire cut off from the wiring adapter..
i have a pioneer deh6800mp and it has led's instead of bulbs.

BennyTRD

I picked up a generic wiring adapter from a local parts store and have had no issue's with the dimmer control. I have a DEH P930 with LED's instead instead of regular incandescent bulbs. Course I have never heard a humming noise to investigate, but I think your problem maybe deeper routed. Do you have amplifier thats hooked up to your head unit?

ETRNL

yes i actually have 2 amps, a sub and a 4channel. thought the only thing conneting them to my head unit is rca's and a remote line.

BennyTRD

I had a humming noise coming through the sterio in my car for a awhile and it turned out to be the cheap RCA's I had running to my amps. I replaced them with some thicker more insulated ones and everything was fine from that point.

ETRNL

i dont think my rca's are the problem i only use rockford fosgates..

ewong

So... I got to be really curious as the WTF actually happened....

I found THIS site to have the anawers I was looking for
http://www.sci-ed-ga.org/modules/mat...ght/index.html

Pay particular attention to this module
http://www.sci-ed-ga.org/modules/mat...section_09.pdf

Most cars wire the dimmer like this

+12v battery
variable resistor
tap for radio dimmer
dash lights in parallel
ground

Toyota does it the opposite way


+12v battery
dash lights in parallel
tap for radio dimmer
variable resistor
ground

This means that radios with dimmer lights that are used in Toyotas have the light bulbs GROUND isolated from the Radio's ground!!!!

Most aftermarket radio's dont do this BTW....

Some other key facts

The resistance of light bulbs CHANGE with the light.
At room temp (unlt) the bulb has a very low resistance.
Once the bulb lights it has a very high resistance (i.e pulls a small amout of current)
This means when bulbs FIRST turn on the pull a tremendous amount of current. Of couse the bulbs light and then resitance increases and the current draw drops.
Usually the huge inrush current is NOT enough to melt the fuse as the wire doesnt heat up enough.

So big whoopie do - when we connect a radio's dimmer input to a Toyota dimmer wire... we connect the dash lights in SERIES with the radio's internal light bulb. So what???

Well here what I think happens.

A light bulb needs TWO things to light
-- current flwo though the filament
-- VOLTAGE potential across the bulb.

Now Im guessing here..... but when the bulbs were connected in series, the voltage drop across EACH bult (the radio and the rest of the dash lights) was NOT ENOUGH to cause the filament to "incadesce"

So

That means that the bulb acted as a "short" and as noted earlier - if the filament is not "incadecing" - its designed to pull a TON of current... and keep pulling it till it incadesces. My THEORY is that since the voltage was low enought - the bulbs pulled the current.

Now - the question is why in YOUR case the tail lgith fuse just didnt pop...
See post by Nuthuts96 - his fuse popped.
Why did the harness melt?

I vaguely recall something about foglights... how were THOSE wired?

My guess is that you didnt know that the REST of the lights inthe Toyota are ALSO wired ground switched... so my guess is that the fog lights were wired to the tail lights so that they could turn on with the tail lights and that the fog lights allowed a "dual feed" of current into the dash harness.

Ya didnt pop the fuses becuase the current had more than one path to take (i.e. the wire was designed to hold 10 amps of current, but becuase ya cross feed the fuses you could pull 30amps of current through two fuese and thus melted the wires...)

ETRNL

this how my fog lights where wired..
i stole the pic from this thread wich i followed but changed where i got my power from..
https://www.yotatech.com/forums/f127/factory-fog-lamp-re-wire-mod-3rd-gen-4runner-75177/



before i connected the wire i tested the plug. It is a 12v acc basically.. so my fogs have power as soon as the key is turned. i like to think that i am mechanically/electrically inclined but sometimes i wonder.. by the way the dealership said that even though they dont recomend mods the specific ones i did did not cause/were not involed with the wire burning..

ewong

So the fogs were relayed...

BTW - its techically a "non legal" way to wire fogs - by law they are supposed to turn OFF with the high beams and ON with the lows...

One could wire a swithc to select between a low beam only (legal way) or accessory (more useful way)... not that I have anything like that in my truck - no sir

so still wondering how your mess occured...

weiln

I could have sworn on the radios I installed, that there were 2 dimmer wires. I've installed Kenwood and Pioneer, but they both had 2 different dimmer wires. One for most American vehicles, and the other for foreign. There was a specific warning not to switch them, because this is bad.

Don't you just need to make sure you use the correct dimmer wire on the deck when installing into a Toyota?

4Crawler

iTrader: (3)

Yes, if the radio is set up that way, by all means hook it up according to their directions. All the radios I have worked with have only had one backlight wire (with the other end of the bulbh connected to the chassis ground. On those, I just hook the light wire to a switched power wire or to the parking light circuit. Not dimmable but usually works fine.

crbocaj125

I just tried to move my fog wire over to that spot, but it is closed. Can I use the hole on either side? I want mine to be able to go on without the parking lights.