Wiring up questions '47 truck

[GB SISSON]

Picked up a tank from a '59 panel this weekend from CL. Mine is a '47, but they are very close match. Mine was perforated pretty badly and crunched by a forklift. This looks to have a nice sender too. I plan to run 12 v in the panel truck. Will this '59 sender work with the gauge in my panel after I reduce voltage in my gauges? Next question is the horn relay. There were dual horns which I'd like to re-use. The relay has a tab on bottom side of photo labled battery. I will assume the other goes to horn switch, which I plan to mount on cab ceiling with a pull down string to activate. Will this switch be to a hot wire or to a ground, perhaps the roof itself? Lastly I have found the wire that feeds the gas gauge, the oil pressure gauge and the temp gauge. I hooked this wire to power through a voltage reducer. At that point I figured the way to tell if an instrument worked I needed to ground the wire to the sender briefly and gauge needle should start to climb. None of the 3 do. With this test all 3 read as dead. I suppose the reducer I'm using from '60 ford instrument panel might not work. Is this a valid test of gauges?

[Hivolt5.0]

GB Sisson:
1. Yes, the fuel sender should work with a 12v system as long as you use a voltage reducer on the gauges.
2. The horn relay: The battery connection goes to constant power. If you are converting to 12v you need to get a relay rated for that. One of the connections goes to the horns and the third is the switch. From the factory, the "signal" wire would go to the horn switch which would ground the circuit. I'm not sure how a pull string switch works so you'll need to read the instructions on that.
3. So you found the wire that powers the three gauges? If this is true, then on the back of the gauges there are the wires that run to the respective senders. You need to ground the senders, not the wire between the sender and gauge. The temp and oil sending units get their ground from the engine (do not use thread sealant) and the fuel sender has an extra wire grounding the sender to the body. Also, the senders need something to "sense". So the fuel sender you can move the float which should activate the fuel gauge. The temperature sender you could submerge in hot water to test the gauge. The oil pressure, I'm not on that one.

I hope this helps and good luck!

[GB SISSON]

Thanks very much. This gives me much needed information. I plan to make a simple roof switch. I grew up at the bottom of a steep hill leading away from a Standard Oil refinery. Trucks ground their way up the hill every 1/2 hour around the clock. We would often look at the driver and do a double fist pump and they'd respond with a couple short but loud horn blasts from a string or lanyard coming down from the overhead. It may have been a loop of cord, which would be much easier to find in an emergency. Always wanted one of those and I'm thinking a wood clothes pin might be the basis for a grounding switch. As I write, I'm thinking they were air horns on the roof with a valve cord, not a switch like mine will be. Trucks with single circuit master cylinders need good horns.

[Hivolt5.0]

Have you considered converting the single circuit master cylinder to dual? I'm restoring a '48 F4 for a gentleman and I converted his to a dual circuit. The biggest thing is to find a master cylinder with at least the same bore size as the original.

[GB SISSON]

Can you share what you found? I have a one ton and a two ton both 47s. Did you fabricate brackets? Both mc's are brand new so it won't happen right away, but it interests me.

[Hivolt5.0]

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Here's a post I had on brake line size. Scroll down and you'll see pics of my setup.

https://www.fordbarn.com/forum/showthread.php?t=130250

The engine has been updated to a 302/AOD combo but everything else is stock.

[Hivolt5.0]

If you're a member on the HAMB here's my build thread. Check out pages 8 & 9 for more pics of the MC.

http://www.jalopyjournal.com/forum/t....642173/page-8

[Juergen]

Originally Posted by Hivolt5.0

GB Sisson:
1. Yes, the fuel sender should work with a 12v system as long as you use a voltage reducer on the gauges.
2. The horn relay: The battery connection goes to constant power. If you are converting to 12v you need to get a relay rated for that. One of the connections goes to the horns and the third is the switch. From the factory, the "signal" wire would go to the horn switch which would ground the circuit. I'm not sure how a pull string switch works so you'll need to read the instructions on that.
3. So you found the wire that powers the three gauges? If this is true, then on the back of the gauges there are the wires that run to the respective senders. You need to ground the senders, not the wire between the sender and gauge. The temp and oil sending units get their ground from the engine (do not use thread sealant) and the fuel sender has an extra wire grounding the sender to the body. Also, the senders need something to "sense". So the fuel sender you can move the float which should activate the fuel gauge. The temperature sender you could submerge in hot water to test the gauge. The oil pressure, I'm not on that one.

I hope this helps and good luck!

Agree with responses 1 and 2 but why isn't grounding the wire between the sensor and the gauge the same as grounding the sensor? It shouldn't matter if I ground the wire at the sensor or somewhere in between.

My question would be how did you wire the voltage reducer? There are several types; one is simply a two port resistor and another is a three port voltage divider. If using the first type, the resistance may be too high causing nearly no voltage at the gauge. To make sure this is not the case, measure the voltage at the gauge power source after the voltage reducer and the sensor as the load. It should be 6 volts. Also measure that the voltage into the reducer is nearly 12 volts. If not the problem could be the reducer or the wiring.

[GB SISSON]

Thank you. I will try to get these readings with my multi tester. I am very bad with electrical stuff. Multi testers and electricity in general befuddle me.