I recently installed a Sony head unit and did the whole wiring process. I didn’t have a wire to splice to the dimmer wire on the conversion harness. Is there something I’m missing? When driving at night I have to manually adjust the brightness. Is there a way to dim it when the headlights come on or something?

 

What year is your Blazer?

 

It’s a 1998

 

OK, then the attached scanned schematics might help. These are for my 1999 Blazer.

Look for pins 6 and 7 on connector C1 (on the radio). These appear to be control signals for the display dimming. It looks that there is a switched 12V supply and also a connection to the dimming circuit.

On page 8-273, circuit 1220 (pin 7 on connector 1) is the variable voltage from the dimmer in the headlamp switch.

On page 8-274, circuit 1382 (pin 6 on connector 1) appears to be a switched 12V signal that goes to the radio originating from the Body Control Module. Be careful of stray electrostatic discharges around the BCM.

 

I am completely ignorant when it comes to anything electric. Are you saying there is a place I can splice the dimming wire from the radio?

 

It depends on how the dimming circuit on the new head unit is wired.

If you are not able to understand the way the circuit supposed to work, then I'd suggest you find an expert an/or contact the manufacturer's customer support.

What you need is to know the type of input signal voltage the head unit uses to set the readout intemsity and then if the original signal voltage that comes from the truck is the same.

Measurements of the stock signal supply woukd have to be completed to make this comparison.

 

Some conversion harness adapters omit a wire for the dimmer. You may have to splice a wire directly from the radio harness to the factory dimmer wire.

There should be a dimmer wire in the factory harness that will change voltage (measured with a multi-meter) as you adjust the dimmer. On a 98 the factory harness should be in 3 or 4 sections for the plug (Connectors C1 and C2 in the diagram sent by Christine). The two smaller 4 pin sections (pins 1-4 and 17-20) will have the front and rear speaker wires, and the 3rd section will have your power, ground, and ignition wires. The dimmer wire should be in the same section as the power, ground, and ignition wires. I can't remember if it's the purple/white (pin 6) or the grey (pin 7) that will work for an aftermarket radio. I believe the ppl/white will vary resistance, and I believe it is a grounding -12v signal. I believe the grey will be a constant +12v when the headlights are on.

Hope this helps narrow it down a bit.