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Discussion Starter #1
Has anyone bought a '65-'66 instrument panel constant voltage supply from Mustangs unlimited recently? I have been through two of them since Labor day. The first one lasted less than 20 hours, the latest one only lasted 1 hour. The first one failed gradually with the instrument readings being much lower than they should be. For example, with a full tank of gas the fuel gage read 1/2. The second simply failed completely with both temperature and fuel gages reading the same as if the key was turned off. I'm thinking that Mustangs Unlimited got a batch of bad parts from their supplier.

However, is there something about my car that could be killing these things? The car has the standard '65 dash with warning lights. It is completely stock and mostly original. I replaced the original constant voltage supply Labor day weekend with the first unit from Mustangs Unlimited. Instruments worked fine until last week when they started reading low. Replaced with second unit from Mustangs Unlimited and drove the car one hour to a show Saturday. Checked gages while driving home and both were reading as if the key was turned off. They came to life briefly while driving home but then died again and haven't worked since.
 
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Is this the new version that most retailers sell for around 60 dollars? If so I swear that there was a recall on them. Or am I thinking of something else? Either way I wuld get my money back and go with a stock replacement type.
 

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Discussion Starter #3
The ones I bought are the original replacement type that Mustangs Unlimited sells for about $25.00. They are not marked with a manufacturer's name.
 

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I went through a couple of bad ones about two years ago, lo and behold, they weren't returnable being electrical parts.
I'm now using the NPD electronic version in my Boss, I have another one to go into the 'vert.

Carl
 

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Inertia 500 said:
Has anyone bought a '65-'66 instrument panel constant voltage supply from Mustangs unlimited recently? I have been through two of them since Labor day.
Do they require heatsinking to avoid overheating?

An easy and reliable way is to just pick up an LM7805 three pin IC regulator from any parts house, Radio Shack, or even ebay.

http://www.national.com/ds/LM/LM109.pdf

These will take up to 35 volts and give a nice regulated 5 volts at up to 1 amp (properly heatsinked). Pin one is the 12 volt input, pin two is grounded, pin three is the 5 volt output. Easy. The LM7805 also has both overcurrent and thermal shutdown protection, so even if the car has a problem that loads the regulator, it will shut down without damage.

John
 

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Discussion Starter #6
Thanks, John for the great suggestion.

To answer your question, the original equipment regulator does not require heat sinking. It is completely mechanical consisting of a set of contacts that are opened and closed by a bimetalic arm with a very small resistance wire wound around it. When the contacts are closed, current flows through the resistance wire, heating the bimetalic arm, which causes it to move and open the contacts. This stops the flow of current through the resistance wire so the bimetalic arm cools until it moves back to where the contacts close again. The regulator is wired in series with the gages, which are grounded through their respective sending units. The constant opening and closing of the contacts results in an average 5 volts supplied to the gages.
 

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Discussion Starter #7
John,

I found the 7805 regulator on the Radio Shack website. They offer several different heat sinks for T0-220 devices. Do you think a heatsink is necessary?

Also, does the case (tab?) have to be insulated from ground?
 

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I didn't know the regulators you are having problems with are original mechanical ones.

Inertia 500 said:
John,

I found the 7805 regulator on the Radio Shack website. They offer several different heat sinks for T0-220 devices. Do you think a heatsink is necessary?
It depends on the current draw from the instrument cluster. Since this regulator is small and the leads delicate, I would use a heatsink for making an easier, sturdier mounting system as well as getting the cooling effect.

Inertia 500 said:
Also, does the case (tab?) have to be insulated from ground?
No, it doesn't need to be isolated, nor does it need to be grounded. The metal tab is connected directly to the middle (number 2) pin which is actually ground anyway. The nice thing about the tab being grounded on this regulator IC is that you don't have to worry about isolating the tab as you would with a transistor with the same TO-220 case.

John
 
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