Adding Guages

The attached drawing shows the Model A electrical system in a simple diagram as Henry designed it. It is shown as a positive ground. By reversing the polarity designations at the battery it becomes a negative ground. It can be either six or twelve volts.

The way Henry designed it was his idea of theft prevention. The ignition switch when switched off puts a ground on the points. The wire from the ignition switch to the distributor is protected by an armored cable. The cable is attached to the engine with the number 8 head bolt. This makes it extremely difficult to hot wire a Model A. To do so you would have to unbolt the cable from the engine and remove the distributor to unscrew the distributor from the cable; then reinstall the distributor and screw in a bypass cable with a jumper wire that would clip on to the low side of the coil.

This design does not allow for any electrical accessory to be attached to the ignition switch because any device attached there would be drawing current thought the coil and be arallel the ignition points.

In order to have accessories attached to the ignition switch you would have to do some rewiring of the circuit. There would have to be a direct connection between the coil and the ignition points and the ignition switch would have to be above the coil and switch power to the coil on and off.

The Model A would them be easy to hot wire.

Tom Endy
 

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Moto meter is all you need. Oil pressure gauge basically useless on A. Oil pump is bulletproof and none of the bearings are pressure fed anyway.
 
jhowes said:
Ruth ' thanks for the reply but the line to the points goes through the ignition switch and it has to be broken and tied directly to the coil which is where I have my problem. This is the same as I figured out but to put a line from the coil through the ignition switch housing that's hooked to the wire that goes to the points and another pair feeding power to the rest of the car which also has to go through the switch to be turned on and off'. That makes for three wires in the ignition switch housing which I don't think is possible. Jack
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If I am understanding you correctly you want to route all your power thru the ignition switch? I don't think you should try that. The switch wasn't designed for the many amps.
 
I am starting to install a volt meter and a water temp gauge on my 1929 coupe and seen these posts. It seems like an oil pressure gauge is useless. The oil press and distributor are both run off of the cam shaft, if cam or distributor stop working it really doesn't matter if you have oil pressure or not, engine quits you lose pressure, engine runs you have oil pressure...am I thinking right or not?
 
It wouid be worthwhile to at least have an idiot light for oil pressure (IMHO). Another scenario to the ones you cited would be engine oil level is very low or crankcase is empty. The engine would be running with zero oil circulation and would seize. Maybe we are spoiled by modern engine monitoring systems, but knowing engine oil pressure and engine temperature at all times is good info which was not known on Model As but did become available with standard equipment on cars a short time later.
 
The oil pressure gauge is one step up from an idiot light. You learn what your normal pressure is, and then if the gauge indicates a drop in pressure, you stop the car immediately until you figure out where the problem is. Could be oil pump failure, could be a leak, etc., but either way the gauge is telling you to stop before the lack of oil flow damages the engine.
 
To figure out how to wire an A so that the coil is after the ignition switch, search "8n wiring diagram", which is for a tractor. Sorry, I don't know how to post it here. All that's needed is a different junction block which costs a few dollars.
 
One more note about oil gauges - in Fahnestock's "Unauthorized Accessories," the only two gauges advertised are oil and temperature gauges. So there seems to have been demand for oil gauges at the time. There are also red/green idiot lights for detection of low oil pressure.
 
Y-Blockhead said:
Hoz about something like THIS?

43101806011_4d32dcae08.jpg

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Personally I don't like the flashy look of modern gauges in a Model A.
 
alexiskai said:
There are also red/green idiot lights for detection of low oil pressure.
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I wonder if low oil pressure switches for indicator lights are set low enough for the Model A or would the light be on all the time. Mine only shows ~2-3 psig at idle
 
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Ruth said:
I wonder if low oil pressure switches for indicator lights are set low enough for the Model A or would the light be on all the time. Mine only shows ~2-3 psig at idle
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There were contemporary lights that were sensitive enough.

IMG_3144.jpg

PS - I assume "indicates generator and fan belt trouble" means like "if the light is off, you have generator trouble."
 
alexiskai said:
There were contemporary lights that were sensitive enough.

View attachment 452990

PS - I assume "indicates generator and fan belt trouble" means like "if the light is off, you have generator trouble."
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Wow. I didn’t know the “idiot light” was available way back in 1929. I had just assumed it was a late 1950s thing. (I think my 1957 Fairlane had idiot lights.)

Thanks for sharing.

Sent from my iPhone using Tapatalk
 
denis4x4 said:
The only reason to have an oil pressure gauge is to panic passengers when it reads 0 to 5 PSI. I have a volt meter and vacuum gauge. The MotoMeter is more than enough for water temp.
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Someone tried to steal my moto-meter, and broke the neck on my nearly new radiator. $500 bucks shot. I have a new radiator, and a gauge now... I sure miss my moto-meter though.
 
I have heard that Henry didn’t think a temp gauge was necessary, nor was a motometer, which he resisted offering. His comment, supposedly, was, "Any fool can look out over the hood and see if the radiator is boiling over or steaming." Anecdotal, maybe.
 
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