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Discussion Starter #1
I have been working on my 1970 Mustang with my Dad. He has addressed to me that the lights that are supposed to light up the individual gauges to see them at night do not work. The headlight switch has been replaced recently so I don't think that it is the culprit. Automotive wiring, electricity, etc is not my specialty or strong point, but I sort of know that there are switches, fuses, resistors, and other stuff involved. Could the bulbs just be bad? I also got a suggestion from a friend that a circuit could have burned out since the cluster lights were ran on a printed circuit for 1970. So could this also mean that there is a possibility that the courtesy light circuit is bad? If so, can it be replaced by someone who has had little experience with electrical work?
 

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Most often the problems I have seen with those clusters is the printed circuit on the backside of the unit.
 

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The easy stuff first. Do you know that you can rotate the headlight switch knob to brighten and darken the instrument bulbs? The switch could be rotated all the way to dim which turns the lights off.
 

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Discussion Starter #4
The easy stuff first. Do you know that you can rotate the headlight switch knob to brighten and darken the instrument bulbs? The switch could be rotated all the way to dim which turns the lights off.
I didn't know about the instrument bulb dimmer part. I did know there was some sorta coil that was part of the switch. That means that coil was what dimmed the instrument bulbs. Now the next thing is, could it be the printed circuit or a fuse?
 

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Discussion Starter #5 (Edited)
Most often the problems I have seen with those clusters is the printed circuit on the backside of the unit.
A friend told me about that. I have started to see if I could find a printed circuit online.
 

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Too easy. This is the standard non-tach version.

 

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This is where you need a voltmeter. Nothing special. just a cheap digital voltmeter that also measures resistance and the wiring diagram would be nice too.

First thing check to see if there is a dash light fuse. Its been 35 year's since my last "running"'70 Boss 302. I don't remember if they had a fuse or not?

Next pull the instrument cluster and identify the wire coming from the headlight switch and probe it with a test light hooked up to ground. If it lights up your good up to the circuit boar. Your circuit board could have a break in the dash light circuit, or all the bulbs are burned out, or they do not have a good ground. or you have a bad connection between the wiring harness and the circuit board. It has to be one of those four things.

The bulbs could all be bad. I've been in o '65-'66 dashes where all the bulbs were black and burned-out. They all last about the same time and if one burns out they should all be replaced. I've replaced one taillight at work only to have the other taillight burn out the next day. After that I always replace them both. If you have the cluster out I'd replace all the bulbs while your there. I've been in lots of '65'-66 dashes but they have individual wires, no printed circuit boards. Never been into a '70 Mustang dash. I have '70 Boss 302 "project" in the driveway so I will eventually be getting a dash lesson.

If you have power to the printed circuit board then I would look at the printed circuit board, following the dash light circuit from the bulbs back to the harness plug. If the little copper strip is broken you should be able to see it. If you had a voltmeter with a continuity tester you could check the circuit to see if it is complete from the plug to the bulbs.

I'm on several Ford forums and about twice a day I tell people they "must have" a voltmeter if they are going to continue working on cars as a hobby. It takes all of the guess work out of it electrical diagnosing. You can learn to use one in just a few minutes. I use mine at least once a month on my projects or on friends and neighbors. Then least when you ask a question on a forum you can tell them what voltage readings you are getting and then we can begin to narrow down the problem. This is a very basic circuit.

Maybe someone can give him the color code of the dash light wire going to the printed circuit board so he can check it for voltage. My set of '70 Ford Shop manuals are boxed up and stored away.

There are all kinds of printed circuit board repair kits.
 

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When you get it working, I recommend LED bulbs. You'll be stunned how much better everything looks, unless you just have to have that vintage warm fuzzy glow. Some dimmable LEDs are even available now.
 
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I'd check the fuse first, as well as checking for the presence of power at the fuse box. Second thing I'd check is that the headlight switch rheostat knob is turned all the way to the "bright" position. After that, its "work you way down the circuit from the last point of power".
 

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This is a schematic for a 69. The 70 is similar. The schematic shows how it works, not wire colors or plugs, etc.
Power for the lights goes through the variable resistor (the spring looking thing you mentioned), to fuse #5 and then to 13 lights. If any of the ash tray, heater, radio, or clock lights work, then you have power in the circuit and it may be the printed circuit for the dash. Its possible all 8 dash lights could to burned out, or the ground for the printed circuit may be loose. Time for the volt/ohm meter that was mentioned earlier.
 
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