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Old 02-13-2010, 09:48 PM
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wiring a early 40 car

I just finished installing a SBC into my 40 car. Now its time to wire it. Using the original dash and gauges. Which consist of a mechanical speedometer thats easy to hookup. But the other original gauges are all electric. Fuel,Temp,Oil and Amp. All 6 volt. So I have two questions. All the original gauges are 6 volt. But now the car is a 12 volt. Will or how will the original gauges work correctly? Also all of my new sending units are electric 12 volt. Except for the oil pressure,its mechanical. Do the make a electric oil pressure sending unit, that will fit the SB Chevy ?

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Old 02-14-2010, 09:03 AM
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Some points to consider:

- You can run the engine with 12v, and get a 12v to 6v converter so that the original gauges can be powered by the new engine.
- The amp gauge is probably a full current gauge, which requires full current running to the dash, and it is generally too dangerous to use with modern alternators. A voltmeter is much simpler and less risky.
- You need to know the original resistance of the old sending units to determine if you can find modern equivalents for the fuel and temp gauges. For example, many newer GM cars use a 0-90 ohm sender. However, that would not not work with a dash gauge that was expecting a 0-60 ohm sender.
- Electric oil pressure gauges and sending units are easy to find, but you might be able to use the old mechanical gauge. If you use steel tubing (or maybe even brass) to connect it to the engine, it should work well. However, you need a gauge range that goes up to about 60 psi for a good SBC.

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Old 02-16-2010, 07:35 AM

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Don't put 12 volts on those 6 volt gauges!!! They will burn out instantly. To do the job right and the cheapest, is to use the 6 volt oil pressure, coolant temp, and fuel sending units. The ammeter will be good if it is the induction type (wire going through a loop on the back of the gauge). You need to buy a 12 volt to 6 volt step down unit to power the gauges. You can go to the local auto parts store and buy a cheap one that will not work and can burn up your gauges so beware. Ron Francis has one that is pricey, but will work for the lifetime of your car and work properly. It is about $50 bucks but is a lot cheaper than a set of gauges. To go a more expensive route, you can send your instruments to a good instrument repair shop and get them modernized to operate on 12 volts for $80 bucks per instrument. If you want to go that route, let me know and I will send you some phone numbers.

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Old 02-16-2010, 12:55 PM
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Classic Instrument seems to be updating old gauges. I suspect it isn't cheap, but is one way to go with a quality part. I've used their gauges with great luck.


Dave W
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Old 02-18-2010, 05:32 PM
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If your guages are good go with a voltage convertor. Classic Instruments conversions are not cheap, around $3500 was my quote on the 47 Chevy.
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