Working dimmer with aftermarket radio?

[Sycobob]

I've done a lot of reading, but I'm having trouble finding the answer I'm looking for. I recently installed a new head unit, and I'm trying to get the dimmer switch to work again. Also, the radio supports dimming with the cars switch so I'd like to get the working too if possible. I know the TCU is good.

I've tried connecting the radios illumination wire to the cars dimmer wire and illumination wire. Neither work. I'm going to try grounding the dimmer wire next, but obviously that won't make the radio dim.

Does anyone know how I can wire things to get the dimmer switch to work again?

[Sycobob]

Small addendum: I now realize that the radio is not going to dim variably, it is only going to be slightly dim or full bright with the parking lights/headlights on or off respectively. This means when I hook up the dimmer wire from the car to the illumination wire from the head unit it dims when I turn on my lights, but not with the dimmer switch in the car. This isn't ideal, but at least it's something. I might be able to adjust the dimmed brightness to a lower setting as it's a barely noticeable difference.

This leaves me with just one question I suppose. How can I get the cars dimmer switch to work now?

[Sycobob]

Bah, I'm sure someone here knows how this works. Does the dimmer normally work if you cut the radio harness? Maybe my switch is bad, I only checked to see if it was closing the circuit when it was pushed up or down. Maybe the logic board in it is bad?

[Sycobob]

When trying another dimmer switch to see if that was the problem I noticed something odd. The dash lights still work when I unplug the dimmer switch. That's not right is it? I wonder if the previous owner messed with the circuit at all.

[whyteboi]

why on earth would you cut into the radio harness. if you would have spent the $4 to get a harness adapter from pretty much any store you wouldn't have had a prob cuz all the wires would have been color coded and labeled

[Sycobob]

1) The harness was cut when I got the car. It already had an aftermarket HU in it.

2) I know exactly what each wire does and everything is hooked up just fine, with the exception of the dimmer circuit, which isn't messed up because of anything I did.

3) Even if I had a harness adapter it wouldn't do me any good, there is clearly something wonky with the circuit that has nothing to do with the radio from what I can gather.

[motoman399]

your dimmer circuit should work with any stereo you put in it. you have another issue going on.

[Sycobob]

Yea that's what I've managed to figure out, so now I have to try and track down the issue. I guess I need to trace the wires and see what's amiss. To be clear though: do the dash lights normally stop working if you unplug the dimmer switch itself?

[whyteboi]

do the dash lights normally stop working if you unplug the dimmer switch itself?

they should still work, my dimmer switch is unpluged (cuz it got busted) and my dash lights and everything works fine, if they dont in urs then you have a prob

[rocksteady_racer]

Concur - i hooked my old sony head unit in to my 240 - I like cutting and soldering the wires too screw harnesses lol. Anyway but my dimmer works fine thru the stock illum wire. So I'm guessing either the head unit is bad or the some where else in your wiring mess there is a prob with the dimmer circuit.

[Sycobob]

It's definitely not the head unit, it works just fine. The dimmer wire is hooked up to it and it dims when I turn on my lights like it's supposed to.

My dash lights still work with the dimmer switch unplugged, but someone told me if they still came on with the switch out then it meant someone had probably bypassed the dimmer switch in the wiring.

This weekend I'm going to start checking different segments of the circuit to see if I can figure out where it's not behaving the way it's supposed to. Thanks for the info guys.

PS rocksteady, how do you have your wires hooked up? When you cut the harness you have a Red-Blue and a Red-Yellow wire that are labeled Illumination and Dimmer in the FSM. One is the 12v that switches on and off with the lights and the other is the one that gets varied voltage. I hooked up the 12v on/off to the radio and just capped the other.