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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

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Old 07-27-2012, 11:12 AM   #1
Chortdakooba
 
Join Date: Jul 2012
Vehicle: 1979 Pace Car
Location: Canada
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Default Instrument Dash Lights Won't Work

The dash lights in my 79 Pace Car will not work. All the other guages, oil pressure, temp etc work fine.

I put in a new headlight switch that did not cure the problem. I also went through all the fuses and found that the slot for the cluster illumination had a 15 amp fuse when it should have been a 5 amp fuse. I switched to a 5 amp as per the handbook. I then pulled the cluster and checked the bulbs as I thought maybe they burned out, but they are fine.

As well, my dome light will not come on when you open the doors, but it will come on when you turn the headlight switch all the way left. I don't know if this problem would be related to the cluster problem or not.

Does anyone have any other ideas or had similar problems?
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Old 07-27-2012, 11:38 AM   #2
javila2468
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check your dim switch...could be faulty.
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Old 07-27-2012, 11:58 AM   #3
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Is there a way to test the dimmer switch? It does switch the lights from low to high and back, so I didn't think that could be the problem.
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Old 07-27-2012, 03:17 PM   #4
Big_Bertha_87
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Same thing with mine. I have to have the dimmer switch at a certain location in order to have lighting in the console.
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Old 07-27-2012, 05:14 PM   #5
Chortdakooba
 
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Thanks for information. I have a new dimmer switch on order and will put it in tomorrow. Although all the cluster bulbs looked fine, I put all new ones in as well.

New dimmer switch, new bulbs and new headlight switch. Hope this all works.
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Old 07-27-2012, 05:19 PM   #6
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Quote:
Originally Posted by Chortdakooba View Post
Is there a way to test the dimmer switch? It does switch the lights from low to high and back, so I didn't think that could be the problem.
If your dimmer is one of the old style aluminum case units then you need to set the meter to a low resistance (ohms) scale and probe across the two silver colored terminals. While holding the probes across the terminals turn the dimmer **** and watch the meter. It should be a fairly smooth increase/decrease in resistance without any 'drop outs' in the reading.
If you have the newer plastic case switch then you probe across terminals R & 1. The identifiers are molded into the case next to each terminal.

To trace for power follow the circuit diagram and check for voltage along the dimmer switch circuit. Take the negative probe and connect it to a metal chassis part/screw and take the red lead and probe the connection points along the circuit. The BR wire behind the main light switch that goes to the back of the dimmer is a good place to start. With the main light switch in the Park position you should have about 12v at both points
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Old 07-28-2012, 05:26 PM   #7
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Well the new dimmer switch didn't work, in fact things got worse. The lights wouldn't even come on. I put the old dimmer switch back on the lights work.

I turned to testing the headlight switch. I noticed pin "A" in the wiring harness doesn't have a wire running into it. One of my tests is to test 12V running to A but there isn't even a wire there. That seems strange as it looks all stock.
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Old 07-28-2012, 11:11 PM   #8
Tony71502
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Have you taken your dash off before? My vote is a pinched wire causing a short.
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Old 07-29-2012, 11:54 AM   #9
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Yes, I have taken the dash off and the instrument cluster, but I didn't see any crimped wires.
Right now I'm trying to find a diagram of the wiring harness for the headlight switch to compare to what I have.
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Old 07-30-2012, 11:25 PM   #10
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This is the complete wiring diagram for 79
http://www.mc-machine.com/pdf/1979.pdf
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Old 07-30-2012, 11:25 PM
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