Headlight switch is dimming running lights instead of interior lights

[Bronco_89]

I am trying to chase down a problem in my son's 1989 Ford Bronco 5.8 XLT where using the dimmer feature of the headlight switch is actually dimming the running lights instead of the interior lights. I think this may have something to do with the way the wiring has been done for the Kenwood radio that was in the vehicle when we bought it.

I've recently replaced the headlight switch for some other issues we had with headlight operability and I've visually inspected the connector for signs of damage based on other posts, but the connector looks good and I think it is the original factory part so I don't think it has been wired incorrectly. However, I am going to verify this. I've also been looking at wiring diagrams to see if they shed any light.

Here are a few things I've tried:

If I completely unplug the radio, the running lights don't even come on and the radio connector only shows 12v at the 'always hot' yellow wire. The accessory wire, illuminator and dimmer wires show 0.1-0.2v no matter what position the ignition switch is in. I was expecting 12v at the accessory line when the ignition switch was in the ACC position.

If I splice in the dimmer wire to the 'always hot' wire, the dashboard lights will come on when the headlight switch is on, but the dimmer functionality will dim the running lights instead of the interior lights. However, the radio will turn off when the headlights are turned on.

If I splice in the illuminator wire to the 'always hot' wire, the interior lights are always on and the dimmer dims the running lights. The radio also turns off in this setup when the headlights are turned on.

If I splice the illuminator wire to the dimmer wire, the running lights don't work nor do the interior lights when the headlights are turned on. This surprised me since there should be 12v on the illuminator wire when the headlights are on.

I was actually trying to get the lights working as expected without a radio connected, but I'm not sure if that can be done without plugging wires into the connector for the radio.

Ideally, I want the radio connected, but my son is opting to listen to music when he should be driving with his lights on, so no radio is the safer option at this point.

Any help is greatly appreciated.

-Bronco_89

 

[miesk5]

yo Bronco_89
 

For now, here is the Wiring Diagram in 87-89 Bronco & F series (Mitchell)
Source: by equivalent (Beetlejuice) at SuperMotors.net

http://www.supermotors.net/registry/7497/31098

Hd lts @ B-D @ 1

 

Main Light Switch @ C-D 14-15



Beam Select Switch is below Main Light Switch @ D-15

Radio @ D-23



Some installers jam the radio harness in and pinch othr wires against metal cross beams, etc.

 

[Bronco_89]

Thank you for the schematics.

The schematics explain why I see the ACC line at the radio drop voltage when the headlights are turned on.

I don't quite follow what the IGN port for the Main Lt SW does?

With the headlights turned off, no matter what position I have the ignition SW in, there is always 12v on the YEL-BLK wire at the radio.

From the schematic it looks like an '89 was wired so that the radio didn't work unless the ignition switch was in the ACC or RUN positions.

However, I am pretty new to reading electirical schematics so I'm sure I'm missing something obvious.

I checked the wires at the radio connectors and the insulation for all the wires appears to be intact.

Thanks again for any and all help.

 

[miesk5]

yo 89,

yw.

the IGN port for the Main Lt SW Black/yellow provides 12+ volts to the switch from Fuse 11 (15 amps); it also feeds Radio & Clock Illumination

 How to Test: The Headlight Switch
(Ford 4.9L, 5.0L, 5.8L)

Verify Pin Identification; looks A-OK to me so far as compared to equivalent (Beetlejuice)'s wiring diagram

Headlight Switch & Connector Pin Out Pin Wire Color Description B1 Black w/ Orange stripe Battery (+) B2 Tan w/ White stripe Battery (+) D1 Lt Green w/ Yellow stripe Power (+) for interior lamps D2 Black w/ Pink stripe To all interior lamps H Red w/ Yellow stripe To headlight dimmer switch I White w/ Lt Blue stripe To instrument panel lamps IGN Yellow w/ Black stripe Battery (+) R Brown To exterior lamps DN Orange w/ Black stripe To radio illumination lamps

 

[Bronco_89]

Thank you Miesk5, I resolved the issue with the use of the information you provided.

I disconnected the dimmer wire from the constant 12v wire feeding into the radio, replaced the 15a fuse for the running lights that had been blown due to the incorrect wiring.

Since there was no voltage on the ACC line at the radio connector, I connected the ACC line for the radio to the constant 12v wire and now the running lights work correctly and do not dim, the panel illumination works correctly and does dim, and the radio does not power off when the lights are turned on. SWEET!

However, foolish me should have checked the fuse for the ACC line while I had everything out since it turns out the fuse was blown and I could have easily replaced it and connected the ACC radio line to the ACC radio connector and had everything working as designed. Now, I get to take it all apart again to fix this.

Thanks again.

- Bronco_89