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-   -   gee whiz whats up with my lights???? (

cutthroatkid 05-22-2010 11:43 AM

gee whiz whats up with my lights????
Ok so in the 80 mustang when I turn the headlights on the brake lights go off any ideas?

matt167 05-22-2010 02:15 PM

check the grounds

ethn_bert 05-22-2010 03:11 PM

The mustang uses four dual filament bulbs in the rear. The left two bulbs share a common ground and the right bulbs share a common ground. First thing first check all the bulbs for burnt/shorted filaments. Then lets check the voltage drop on the two signal/feed wires from the sockets back to the positive terminal of the battery. Then perform a voltage drop from the ground to the negative terminal of the battery. The black wire is the ground, the Light Green and Orange is the Directional and Stop, and the Brown is your parking lamps. Also, don't forget that the parking lamps in the rear share common circuits with the lamps in the front and the illumination inside the car as well. Start isolating sections of the illumination circuit and test them individually. What happens when the brake lamps are on and the turn signal is active? What about when the high beams are flashed with the headlamps off? Start checking these things and post the results in the forum so we can help. Good luck.

cutthroatkid 05-24-2010 08:34 PM luck@all

ethn_bert 05-24-2010 08:39 PM

What did you find? Good signals? What was the voltage drop on ground side?

cutthroatkid 05-24-2010 10:06 PM

Ok well when the headlights are on the brake lights don't work&only the drivers side blinker works,when there off brakes&both blinkers work.The pass parking lamp is out &the 2nd hradlight(closets to grill) is out,my old man told me that he once had a 65 mustang&a bulb went out&messed some other lights up,could that be it?

75gmck25 05-25-2010 09:28 AM

It is definitely a ground problem, either at one of the lights (or sockets) or the dash ground under the instrument panel.

Check all the bulbs first to make sure a corroded socket is not causing the problem. Then verify that every light assembly is grounded using a star washer that cuts into the metal. There are probably two grounds on the rear (one each side), and four on the front (headlights, and each park/turn socket). There might be separate grounds for the side marker lights.


ethn_bert 05-25-2010 11:03 AM

Like I said. You have dual filament bulbs in the rear. Check them to make sure that they are the correct bulbs and are not burnt. There is not multiple grounds for the front lighting system. The front headlamps closest to the grill are your lows and highs The outer bulbs are just lows. The front lamps on the capri and mustang use a common ground on the driver side. The front lamp section wire for ground is black. All four headlamp bulbs, front parking lamps, and front side markers all share this common ground. The power wires going to the passenger headlamps and marker/parking lamps are split from a connector before the connection at the directional, hazard, beam select switch. So I doubt that this is your problem; because you are not having issues with only one side headlamps working. The power going to the directional/stop lamps is after the connection at the directional switch. The light green wire(Pin 7) at the back of your directional switch is the the power feed from the brake lamp fuse and stop lamp switch. Make sure that you have power at this point with the headlamps on. Please perform the voltage drop/signal test like I recommend. It could be a fualty turn signal switch. Check the bulbs in the rear. Replace the burned out headlamp on the passenger side and the parking lamp bulb. Check for proper signals at the sockets when the condition is present. Post results. Good luck. Also, is there any aftermarket wiring jumping from the fuse panel?

cutthroatkid 05-25-2010 11:39 AM

Should the rear parking lights be dounle also?

ethn_bert 05-25-2010 03:45 PM

Yes! You have 4 dual filament bulbs in the rear. That could definetly be your issue.

cutthroatkid 05-28-2010 03:08 PM

The only wire I'm getting juice from is the brown

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