Fuel and oil gauges

[Wiggo]

OK, so two questions in one, really.

 

The D20 (1941 Bodge/Plodge/Whatever) is slowly coming back to life. The wiring harness was such a mess we tore the whole thing out and started over, and now the front end and dash is pretty much done. I want to get all the original gauges working: I know the speedo is good if I drive it with a drill, and the ammeter is hooked up and shows something. The temperature gauge probe was cut off clean, so I need to figure out a repair for that, but that can wait for now.

 

So first, the fuel gauge: the wiring diagram shows three connections on the gauge, one to the ignition and two to the sender in the tank. I have no idea what sender is fitted now, but it was working with an aftermarket fuel gauge and the vehicle is now 12V negative earth. Can I get away with the original gauge? How do I wire it?

 

Next up is the oil pressure side. I have a mechanical aftermarket oil pressure gauge (the type with the very fine plastic pipe to a fitting on the block (heresy, I know, but it is a SBC). The fittings are wrong, but do you reckon I can get away with mastic to seal it into the old gauge (which appeared to have had a very thin metal pipe running to the engine)?

[DrDoctor]

Wiggo,

   As I’m not sure what you’re referring to when you mention “mastic”, I have to ask you a question in return first. Are you referring to an epoxy, such as J-B Weld, or are you referring to tape, such as electrical or duct tape?

   First of all, keep in mind that the engine will put out approximately 30psi of pressure, if not more. No tape will be able to withstand that amount of pressure, and will fail immediately. As for the J-B Weld, I’ve actually seen it used for such repairs, and it actually worked (I’ve also seen it used to “temporarily” fix the threads of a spark plug opening in a head, and that “temporarily” fix lasted for several years!!! It wasn’t my car, and the owner just changed the remaining spark plugs, and left that one spark alone . . .). The key to this method be successful is to completely remove any and all traces of contamination/oil/dirt/etc., work the material into the offending opening as completely as possible, let it cure completely before any attempt to put pressure on your repair. Then, give it a try. You’ll know soon enough if it works, or not. Good luck, and warmest regards.

[Wiggo]

Thanks, Doc! I had no idea that line took that much pressure, so yes, I doubt Sikaflex will hold it. Looks like I need to go the epoxy route...

[knuckleharley]

5 hours ago, Wiggo said:

OK, so two questions in one, really.

 

The D20 (1941 Bodge/Plodge/Whatever) is slowly coming back to life. The wiring harness was such a mess we tore the whole thing out and started over, and now the front end and dash is pretty much done. I want to get all the original gauges working: I know the speedo is good if I drive it with a drill, and the ammeter is hooked up and shows something. The temperature gauge probe was cut off clean, so I need to figure out a repair for that, but that can wait for now.

 

So first, the fuel gauge: the wiring diagram shows three connections on the gauge, one to the ignition and two to the sender in the tank. I have no idea what sender is fitted now, but it was working with an aftermarket fuel gauge and the vehicle is now 12V negative earth. Can I get away with the original gauge? How do I wire it?

 

Next up is the oil pressure side. I have a mechanical aftermarket oil pressure gauge (the type with the very fine plastic pipe to a fitting on the block (heresy, I know, but it is a SBC). The fittings are wrong, but do you reckon I can get away with mastic to seal it into the old gauge (which appeared to have had a very thin metal pipe running to the engine)?

Any reason you can't just use copper tubing from the gauge to the sending unit?

[Jerry Roberts]

... "  So first, the fuel gauge: the wiring diagram shows three connections on the gauge, one to the ignition and two to the sender in the tank. I have no idea what sender is fitted now, but it was working with an aftermarket fuel gauge and the vehicle is now 12V negative earth. Can I get away with the original gauge?  How do I wire it? " ...         You can try an inexpensive voltage reducer from 12 to 6 volts on the hot wire ( the wire to the ignition ) that goes to the gauge and see what happens . As you say there is no telling what sender is in the tank . 

[Andydodge]

Dunno if this is any help but my car with the Poly V8 uses all the stock instruments........speedo, water, amp, oil & fuel..........the Oz Chrysler speedo cable fits straight to the 1940 Speedo, the amp gauge reads amps, the temp gauge is mechanical and fits into a standard sized boss in the intake manifold, the oil gauge uses the spot where a sender unit fitted on the V8 block to bolt a oil line that goes to the gauge and the fuel gauge has a resistor wire in its power circuit and the standard 1940 sender unit in the tank........as knuckle says the mastic won't hold the pressure..............the black plastic lines that aftermarket mechanical oil gauges use come with a small ferrule that is usually the right size for the mopar gauge......have you tried it on the stock oil gauge?..........re the Fuel gauge.....mine is the same as yours, 3 wires...... the wire from the ignition has the 12 volt resistor I mentioned and the 2 wires from the sender unit go to the gauge........the gauge reads slow, and has never read truly full even when it was still a 6 volt system 45yrs ago but it does work albeit slowly with the 12 volt resistor and I'm used to it............lol.............andyd          

[Wiggo]

Thanks, guys. Not using copper, for the simple reason that 1, I don't have any, 2, I don't have any fittings for it and 3, there's plastic pipe coming from the sender anyway. I'll see if the mastic holds, but I just ordered a new pipe kit with olives and an assortment of glands and nuts.

 

Good point about dropping the voltage to the fuel gauge. Anyone know the likely resistance of the sender, and I can at least try to test the gauge on the bench...

[Andydodge]

Wiggo.........the resistor that I used is just a normal ceramic ignition style resistor thats normally used to drop the voltage going to a 12 volt coil.........its been there for 40yrs or so......lol...........andyd

[Branded]

Install a runtz resistor and it will drop the voltage from 12 to 6 volts to your fuel gauge. Mounts directly to the back of the gauge. Use the search feature on the forum there’s a lot of information on the use of runtz resistors. You can buy them from Speedway or from E Bay vendors.

 

https://www.speedwaymotors.com/Speedway-Runtz-12-Volt-to-6-Volt-Voltage-Reducer,2374.html?sku=91064101&utm_medium=CSEGoogle&utm_source=CSE&utm_campaign=CSEGOOGLE&gclid=CjwKCAjwwbHWBRBWEiwAMIV7E9rr2Mazuu0dCKB7FMbycZ6MJPV6BOXYX2I1aoS1VVU-i3mGSIXZqRoCkxQQAvD_BwE

[DJ194950]

Branded,

did you notice that the speedway runtz resistor says  for negative ground only?

Just in case if that polarity change is Not make- just pointing that out for info.

 

DJ

[Branded]

2 hours ago, DJ194950 said:

Branded,

did you notice that the speedway runtz resistor says  for negative ground only?

Just in case if that polarity change is Not make- just pointing that out for info.

 

DJ

Did you notice the original post was made stating he rewired  the car to 12 volt with negative ground.?  If the car had been left 6 volt there would be no need for the runtz resistor.

 

quote:

I have no idea what sender is fitted now, but it was working with an aftermarket fuel gauge and the vehicle is now 12V negative earth. Can I get away with the original gauge? How do I wire it?

 

unquote:

Edited April 10, 2018 by Branded

[Wiggo]

Got me a degree in electronic engineering from a ways back, so I can probably figure it out, but thanks for the resistor tip. I'll probably fit a proper voltage regulator. 

[Branded]

10 minutes ago, Wiggo said:

Got me a degree in electronic engineering from a ways back, so I can probably figure it out, but thanks for the resistor tip. I'll probably fit a proper voltage regulator. 

 

It sounds like you have your issue with the fuel gauge solved then. 

I used the runtz on my 49 Wayfarer and the gauge works perfectly. 

Edited April 10, 2018 by Branded

[Wiggo]

16 minutes ago, Branded said:

 

It sounds like you have your issue with the fuel gauge solved then. 

I used the runtz on my 49 Wayfarer and the gauge works perfectly. 

There are plenty more issues for me to deal with. Out of interest, for you guys with stock early 40's cars, what do you do about things like ignition and oil pressure lights, and indicator repeaters on the dash? I fitted a stomp switch for the headlights, but now I have no way to tell (other than pissed off oncoming traffic flashing me) if I'm on main beam or high beam...

Edited April 10, 2018 by Wiggo

[Andydodge]

Wiggo......from memory when I converted my car to 12 volts I just used the original headlight dipper switch and all the globes incl the high beam indicator were changed to 12 volts, the stock car never came with indicator dash flashers but obviously the flasher can is 12 volts..........also installed H4 headlights and they are easy to see which is high/low beam............also ignition and oil pressure lights didn't come into use till the early to mid 50 as far as I know......andyd