The Stovebolt Site Forums The Shop Area The Electrical Bay Fuel sending unit

Went to 12v on my 53 - 3100. Didn't put a v reducer to fuel gauge but it worked fine. Til I got to a little below a quarter tank. Did I mess up the fuel sending unit (6v) or the gauge (original) .?

Sender does not care about voltage, gauge does. Lots of resistance with full take, low resistance with empty tank, most likely burnt the gauge out.

Joe

You burned up your fuel gauge. I just ordered a new one yesterday. The previous owner converted my 54 3100 to 12v. They did everything they should have to adapt the truck to 12v except step down the voltage from 12v to 6v for the fuel gauge. They are very sensitive. I ran through a series of test to confirm it was a bad fuel gauge but the number one indicator was the volt meter showed 12v entering the gauge. The cheapest replaced I could find was on classicparts.com They even accept a promocode of "stovebolt". You have the choice of 6v or 12v replacement. They are about $10 cheaper than anyone else plus cheaper shipping. With shipping my cost was $63. This is OEM correct for your truck.

http://www.classicparts.com/Fuel-Gauges/products/850/

Beware of absolutes. Always and Never are often wrong. I converted my '55.1 panel to 12v & never thought about the need to reduce the voltage to the gauge. It did read a tad differently but worked none the less. I put over 100K on the truck after the conversion and my gauge never stopped working.

What did the gauge do once you got to 1/4 tank? If you fill the tank what does the gauge read?

Not to cross swords with anyone but....why take the chance? As you know the fuel gauge consist of two coils of which one is in series with the fuel sender. When the sender has little resistance due to fuel level then that coil is at risk when you double the supply voltage. The cure only cost a few bucks, so is it worth it?

Good advise. I should clarify that I'm not saying it's bad or can't help to put a reducer on the gauge. My point is that the sky will fall doom & gloom if you don't isn't necessarily true.

FWIW, In reading this and other related threads here and elsewhere I understand the usual practice is to use a Runtz voltage reducer. Just last week, in collecting parts for, what I hope is a soon install of Sparky's gauges, I checked all the local FLAPS for one. I ended up having to order one from Summit. I checked my other usual antique truck parts suppliers and they all only sold the ceramic-type which it seems most advised against.

I have been using a big ceramic resistor from Radio Shack for 16 years without any problems. The key is to mount them away from other wires or flammable material. I always run with the cowl vent open for fresh air, so the ceramic always has some air moving across it anyway.

joe

There will be no need for heat dissipation for the fuel gauge voltage resistor (a runtz style resistor should be used).

My favorite all time best way is to put a 6.8 volt Zener Diode (stripe facing away from the gauge) right at the terminal and be done with it. DigiKey part number CZ5342B CT-ND for $ 0.89 each.

This way there are no electronics to burn out (other than the passive) and they are small enough to fit right behind the gauge. A barrel splice on one end and a terminal end and then heat shrink over the whole thing so as not to cause a short.

When I had the sender for my 38 Master restored this winter, I checked it out on my bench with a spare dash cluster. Just for fun I ran the voltage up to about 10 volts and the readings stayed accurate.