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Old 09-30-2019, 07:46 PM   #1
50droptop
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Default Gauge wizards - need some help

Ok, here’s the situation. Recently completed build, working the Gremlins out. Car has been converted to 12V (no haters), used a Ford voltage reducer from a 60’s mustang for the power feed to the oil pressure and fuel gauge. Oil pressure gauge worked great and was accurate against a mechanical oil pressure gauge as well. Fuel gauge never worked.

So while troubleshooting the fuel gauge, suddenly the oil pressure gauge stops working. Used a “D” cell battery to confirm the gauges, oil pressure moves fuel doesn’t.

Ok, so need a different fuel gauge. Scrounge through the spares and find a fuel gauge that reads with the “D” cell battery test. Replaced the gauge and decided to test everything before installing back in the dash.

Since the voltage reducer stopped working (could read 12V on 1 pole and 0V on the other), resorted to Runtz. Here are some photos of the “temporary wiring”. Red wire is from ignition side of terminal block to each gauge, black is ground back to body.

Here’s what the results are:

When power is applied, the fuel gauge shoots straight to “FULL”. With my volt meter, I’m getting 12V on the power side of the Runtz and 8V on the gauge side. Figured it was the sending unit, so I removed it from the tank, ran a ground from the housing to the body and moved the float arm.....no change on the gauge. It should be noted that I do not have the original 36 sending unit, but a NOS FAA-9275-B (52-54 Ford wagon). It was my understanding that later model sending units worked on the same principle as the early ones. The needle moving all the way to full is like the sending unit wire is grounded.

So my questions....
Is 8V correct for the power applied to the gauge?

Any ideas why the 60s mustang voltage reducer would have just stopped working?

Will the later model sending unit really work with the early gauges?

Any suggestions on how to move forward with the troubleshooting....I’m stumped.
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Old 09-30-2019, 08:01 PM   #2
donald1950
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Default Re: Gauge wizards - need some help

on all the cars i converted to 12 V i used one of these Ron Francis solid state voltage reducers. on one 1950 car i ran the gauges and the hearer fan on the reducer with no problems. had too many problems with the Ford voltage reducers and assorted other reducers. these Ron Francis units worked flawlessly.....

http://www.ronfrancis.com/searchprod...er&sort_by=ASC
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Old 09-30-2019, 09:37 PM   #3
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Default Re: Gauge wizards - need some help

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Originally Posted by donald1950 View Post
on all the cars i converted to 12 V i used one of these Ron Francis solid state voltage reducers. on one 1950 car i ran the gauges and the hearer fan on the reducer with no problems. had too many problems with the Ford voltage reducers and assorted other reducers. these Ron Francis units worked flawlessly.....

http://www.ronfrancis.com/searchprod...er&sort_by=ASC
Ditto on the Ron Francis unit. I used a VR-1 for my gauges in my '41 Ford. Worked perfectly.
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Old 10-01-2019, 05:37 AM   #4
50droptop
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Default Re: Gauge wizards - need some help

Quote:
Originally Posted by donald1950 View Post
on all the cars i converted to 12 V i used one of these Ron Francis solid state voltage reducers. on one 1950 car i ran the gauges and the hearer fan on the reducer with no problems. had too many problems with the Ford voltage reducers and assorted other reducers. these Ron Francis units worked flawlessly.....

http://www.ronfrancis.com/searchprod...er&sort_by=ASC
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Originally Posted by fordor41 View Post
Ditto on the Ron Francis unit. I used a VR-1 for my gauges in my '41 Ford. Worked perfectly.
Do either of you happen to know what the voltage reading is at the gauge? I’m getting 8V from the Runtz; seems a little high to me.
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Old 10-01-2019, 06:30 AM   #5
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Default Re: Gauge wizards - need some help

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Originally Posted by 50droptop View Post
Do either of you happen to know what the voltage reading is at the gauge? I’m getting 8V from the Runtz; seems a little high to me.
When testing gauges , I've used a older accessories cigarette lighter plug in style adapter that you can adjust voltage with . It's got an adjustment range of 12volts to 2.5 volts , simply by moving a switch . I go thru the voltage range till the gauges are matching . Or as near as possible. These cigarette lighter plug ins were used for various car accessories of the 80-90s and I find new at flea markets for a few dollars . They are good up to 1 amp .
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Old 10-01-2019, 08:03 AM   #6
donald1950
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Default Re: Gauge wizards - need some help

the Ron Francis output, as i recall was about 6.5 to 6.75V.... gauges worked fine. gas, oil pressure and water temp and heater fan...... i used the VR4 unit. it has been on my 53 for 4 years with no problems......
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Old 10-01-2019, 08:39 AM   #7
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Default Re: Gauge wizards - need some help

The mustang style should pulse about 5v to the gauges. I've used them for decades with good success.
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Old 10-01-2019, 09:46 AM   #8
TJ
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Default Re: Gauge wizards - need some help

I've always used the Mustang style reducer and they work fine for me. I had nothing but problems with the Runtz reducers. Also the later gas senders do not work well with the original gauge.
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Old 10-01-2019, 02:01 PM   #9
Ross F-1
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Default Re: Gauge wizards - need some help

The "can" or mounting tab on the Mustang-style VR needs to be grounded for it to work properly.
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Old 10-01-2019, 02:52 PM   #10
50droptop
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Default Re: Gauge wizards - need some help

I've ordered another mustang CVR; I'm guessing maybe I shorted it out or something. Also think I need to find a different fuel tank sender. Anyone got a 36-40 fuel sender to part with?
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Old 10-01-2019, 07:18 PM   #11
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Default Re: Gauge wizards - need some help

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Originally Posted by 50droptop View Post
I've ordered another mustang CVR; I'm guessing maybe I shorted it out or something. Also think I need to find a different fuel tank sender. Anyone got a 36-40 fuel sender to part with?
Don't give up to quick on the sender you have, would be interesting to see you can get it to work. Seems like it should.
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Old 10-01-2019, 08:26 PM   #12
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Default Re: Gauge wizards - need some help

Suspect voltage should be in the 3-5 volt range. 1.5 volt C battery is used to test gauge. Good gauge should move to middle of range. 3 volt c battery moves gauge to end of range

Hope this helps,

Tom
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