Brenjen

So; I put in my ARB switches (3) & connected the appropriate wire to the dimmer. The dimmer has one 12V constant, one ground wire & one 0 - 12V variable (out from the rheostat). I connected my ARB switches to the 0 - 12V variable wire controlled by the rheostat so I could have my switches dim with my dash lights.

Here's the pickle - when I turn the knob to dim my dash lights the switches get brighter......when I turn it back to brighten the dash lights; the switches dim!

I took it apart & could not figure out what the deal was so I just spliced it into the constant 12V going into the dimmer & they light up (no dim function though). My dad swears the wiring on the switches must be wrong but they are all wired correctly according to the diagram.


Does anyone have a clue why this is? It's nagging at me.


EDIT: P.S. the dash lights have worked 100% correctly the entire time; they've never operated backwards to the dimmer

4Crawler

iTrader: (3)

The reason is that the dimming dash lights share a common ground path through the dimmer. Lighted switches typically have a single power lead for the light and it is grounded to the switch ground. So if that is hooked to the dimmer, the switch light is essentially wired in parallel to the dimmer and thus will work opposite to the rest of the dimming lights. When the dimmer is on high brightness (i.e the lowest voltage drop across the dimmer), the switch light will be dim. When the dimmer is on lowest brightness (i.e. the highest voltage drop across the dimmer) the switch light will be the brightest.

Two options are to have a switch light with both light leads available so that it can be wired to the dash light power and to the dimmer/ground path. Or just wire the single switch light lead to constant 12 volts and have a single brightness.

Brenjen

Wiring to the 12V "IN" (lead) is what I did & I'm calling it good, but it was bugging the hell outta' me as to why....with no voltage going to the switch wire it would brighten & then dim when it cranks up to >12V

The truth is, if it's really - REALLY simple I can muddle through w/vehicle electrical systems but if it gets even as complicated as what you just described I'm at a complete loss. To me a ground is a ground is a ground


Thanks 4crawler; I figured you'd have the answer.

4Crawler

iTrader: (3)

It would be so nice if all the switch makers would just supply both leads for the light bulb (or LED) to connect to. Then if I wanted it tied to ground, I could put in a jumper and if I wanted it floating (like Toyota does), I could do it that way.

Sometimes you can put the switch in wired opposite and make it work. That is swap the power and ground connections and use the switch to switch ground instead of power. Then tie the light across the dimming bulb circuit. At least that works for things you want to work when the lights are on and also only works with incandescent bulbs (not LEDs).

Brenjen

So from what I gather, the rheostat is varying the ground instead of the power?

Man....it's hard to be dumb like me with electronics. I understood exactly how to make it dim with the dash lights from your first post but still don't understand why/how it doesn't work tied into the variable voltage & I know you can't write the "vehicle electronics for dummies" handbook in a thread on Yota-Tech lol

I don't feel too bad; my dad has got 50 years of electronics background & a college degree in it & he didn't know why it wouldn't work either.....he's 72 today though & his memory is starting to go South on him so that's probably why he doesn't get it either.....what's my excuse?

4Crawler

iTrader: (3)

Look at the wiring diagram in a Factory Service Manual. Going by the '85 FSM I use:. For the dimming lights you basically have a relay (Tail Light Relay) that supplies 12 volts to all the dimming lights. Then all the lights are tied on one side to that power. The other side of all the dimming lights are tied together and connect to the dimmer/rheostat (i.e. a variable resistor). Then the rheostat connects to ground. So at full brightness, dimmer=minimum resistance, you see 12 volts across the lights, 0 volts across the rheostat. At minimum brightness, you might see 6 volts drop across the rheostat, so the light bulbs only see 6 volts across them, but since they do not tie directly to ground, you'll see 12 volts on one side of the light bulb and 6 volts on the other side (i.e. the side tied to the rheostat). So you'll see a variable voltage across the lights, but that voltage is floating and not referenced to ground. When you measure the voltage relative to ground you are measuring the voltage across the rheostat since it is the part connected to ground. When you put a light bulb between that point where the lights connect to the rheostat and ground, that light bulb is in parallel to the rheostat, not in series with it. Hook up your volt meter again and see what your "variable voltage" is doing, at full brightness, it is likely near 0 volts and at full dim, it is likely 6 volts or higher. So it is basically going opposite of what you want to make your switch's light bulb do the same dimming as the dash lights.

If you have a look at this page:
http://www.electronics-lab.com/artic...ry/circuit.htm

The stock setup is something like this:


where "Load2" is the combination of dimming lights and "Load1" is the dimmer/rheostat.

When you add your lighted switch between the center point and ground, you create a circuit like below:


where "Load3" are the dash lights, "Load1" is the rheostat and "Load2" is your added light bulb.

qdude79

To piggyback off of an old(er) thread:

My dimmer doesn't seem to work at all. Dash lights work, but I doubt they're at their "brightest" setting. Turn the dial, nothing. Now, I have no idea why there even IS a dimmer for dashlights, as I've never wanted them anything but their brightest. In fact, I can't even fathom a scenario where you'd WANT to dim them. Nonetheless, here's my question:

If I pull the plug off the back of the rheostat and "jumper" the connector across, would that automatically give me full brightness? I know there'd be no adjustment, but I just want them their brightest all the time.

TIA

4Crawler

iTrader: (3)

Yep, the dimmer is just a variable resistor in series with the ground side of the dash lights. Shorting out the dimmer connector with a jumper would give you maximum brightness.

I do routinely dim my dash lights way down when out in the back country at night. With no lights around it gets very dark. Having the dash lights too bright hurts the night vision when you are trying to see what you are trying to drive through.

okie81

I am having the exact same problem with a boost gauge I installed, thanks for the information

qdude79

Thanks 'Crawler! I'll try it!

Never had the night vision experience, maybe I'll regret it someday. Then again, I'm no brighter than the dash lights...

qdude79

Follow up: Yesterday I pulled the rheostat, unplugged it. It's a three-prong connector (at least on my year/model) that looks like this: l_l

After some trial and error, and two blown 15A tail light fuses, I discovered that running a jumper between the two parallel connectors did the trick! FULL brightness. For the record, the connector has female spade terminal connections. Male spade connectors is what you'll want to use for your jumper.

PS- The perpendicular "third" connection was not used (untouched, unplugged).

Thanks again for the help, guys.

Qdude

qdude79

bumpus