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I am converting my '54 3100 to 12v. Only a couple of items left....fuel gauge and heater motor/switch.
My question is about the fuel gauge. I'm using a NAPA IR4 voltage reducer. I disconnected the fuel gauge wire from the key switch and connected it to the output side of the IR4. I ran a new wire from the key switch to the IGN terminal of the IR4. When the key is in the ON position, the fuel gauge doesn't move. Note: there is very little gas in the tank. I plan to put 10 - 12 gals in it tomorrow. However, using the troubleshooting guide from FIFTH AVENUE I have determined the wire from the fuel gauge to the tank is good, the ground at the tank is good. My test light is lit bright when key switch is ON and I'm testing the IGN terminal of the IR4. Here's my concern -- with the key switch still in the ON position, I touch my test light to the output side of the IR4 and the light blinks (yeah, like a flasher) I also tested at the fuel guage, (output of the IR4 side) and the test light blinks. This doesn't seem right to me. What is my next step? Replace the IR4?

sfsutton,

I'm not familiar with the voltage reducer you are using, but I wonder if it is suppose to behave this way normally, or could the load of your test light be causing this behavior.

Before I replaced this unit, I would use a voltmeter and see if it is actually dropping the voltage to 6 volts.

If that proves, I would test the gauge by pulling the wire at the sending unit. There are three options as I see it...bum gauge, broken sending unit or faulty voltage reducer.

I haven't seen the Fifth Avenue troubleshooting directions, but if they are complete and accurate, you should be able to determine if the gauge or sender is at fault.

Before you toss your new voltage reducer, make sure it is not working...with a volt meter!

Remember that when you probe the output side, you must have a load on it...a light bulb or something to draw some current, otherwise you will see the same value as the supply voltage (I think).

Lots of folks claim they have run 12 volts through the gas gauge for years without problems. If you feel frisky, you could prove the gauge and sending unit 'without' the IR4 in series. This would take that unknown out of the equation and get you back square one.

Just for grins, probe the ignition switch itself, when turned on, and see if incoming power is 'blinking'.

Stuart

The IR4 sounds like it is a pulse regulated regulator as used on European and some U.S. cars(not GM) fuel gauges. I don't know if it would work on a fuel gauge not originally equipt with it, if that is what it is.

sfsutton,

I searched NAPA and found this item. It is described as a 'Instrument cluster voltage reducer', it is $35.00 and vaguely looks like a plug in flasher unit.

This certainly isn't the inexpensive ceramic voltage dropping resistor shown in the specialty suppliers catalog to stick ahead of fuel gauges when changing to 12 volts.

As Baldy noted, this might not be the proper device for this application...will NAPA take returns on electrical items?

Stuart

Thanks for the replies. Yeah, it seems I'm getting my education through my charge card. I found a 12V conversion plan on the internet as soomeone was sharing their plan and parts for upgrading their AD. Seemed thoughtful too me, so I followed it. This was early in the game (before recieving catalogs). The IR4 is pricey compared to what what other candidates cost.

I was thinking last night, my test light might be doing the blinking. It only does it on the output side of the IR4. I'm going to "invest in a volt meter". I've needed one for years. I hope it comes with directions!

For those newer than me at this...the fuel gauge troubleshooting guide at FIFTH AVENUE imo is excellent.

"This certainly isn't the inexpensive ceramic voltage dropping resistor shown in the specialty suppliers catalog to stick ahead of fuel gauges when changing to 12 volts."

The resistor recommended by most 6v-12v conversion guides is a Runtz-style resistor. That can cost as much as $20 from some vendors but Classic parts has it for under $10.00.

Tim

Would never ever consider running 12 volts thru a 6 volt gas gauge. Been there done that. Takes a millisecond to ruin it.

Brand name "Runtz" is what you want.

After researching some of the old posts on fuel gauges, I tend to agree with Bill (olblu49)...

Many members mention hooking 12 volts to the fuel gauge and seeing the magic smoke appear.

Consider me a 'Runtz' voltage reducer advocate.

Stuart

i learned the hard way on those gas gauges - they do not like 12 volts and they sure don't give them away either! a runtz or similiar device is the way to go.

i learned the hard way on those gas gauges - they do not like 12 volts and they sure don't give them away either! a runtz or similiar device is the way to go.