Gas tank wiring question

I have a '51 Fleetline (avatar) it has recently had a 283 / powerglide installed , a Nova rear , complete 1963 Belair wiring harness , the steering column out of the '63 , I have moved the master cylinder from under the floor up to the firewall, question is , the car has a gas tank out of a Geo Metro.... no way to tell how much gas is in it . I want to find a gas tank that I can wire up to the original 6 volt gas guage, I had to rewire the rear section of the wiring harness in the car due to the wire just being to rough to use ,and I didnt run the wiring for the gas tank , so I need to know how to run the wiring to run a gas tank out of a '80's GM car , to run the wiring from the 6 volt guage , to the late model tank , and make it function , can it be done? any help is appreciated..

 

To make the 51 gas gauge work, you will have to mount the 51 sending unit in your new tank. Then you will need a runtz to operate the 6V gauge on 12Vs. I got mine from Ebay. Do an Ebay search and a search here for more info.

My 6V sending unit was an adjustable SW 6V. You should measure the depth of the 51 tank and find a tank with the same depth for the 51 sending unit to read correctly. The sending unit must match the gauge. I doubt seriously you will ever find anything modern to work with your gauge. If you don't have the original tank and sending unit check to see if someone is making a reproduction 51 unit. If not then you will have to find a good used sending unit.

 

"you will need a runtz to operate the 6V gauge on 12Vs".....whats a runtz?

 

it's a resistor, that drops the 12v down to 6v so you don't burn up anything that's 6V.

 

I see you can get those on EBAY , but , can those be bought at the local parts store?

 

Do you know at what ohms resistance the gauge reads full and at what ohms it reads empty? If so, you can probably find a float that reads similarly.

I have used resistors at the gauge in parallel with the gauge to change what the float reading "appeared" to be. I was using a GM gauge with a Ford float

 

I had a hard time finding a local parts guy that was familiar enough with them to order one. They know O2 sensors and TPS sensors but not these things. They wanted to sell me a 40 dollar reducer. I got the runtz from Ebay cheaper than anywhere else. I'm too poor to worry about convenience. Prices were all over the board.

I don't know the technical theory but they are not a resistor as we know them. Back in the dark ages we got a big white round ceramic resistor when we converted to 12Vs This thing is tiny by comparison. 3 wires...12V in, a ground, and 6Vs out to the gauge. Pretty damn simple.

 

Some body on the hamb has got to know the required ohms for the gauge and the sender.
Probably even know what the specs are for the Geo unit.
I'd start another thread for that info because its not a wiring issue at That point.

Couple months ago, two different magazines had tech articles on the resistor needed. Less than couple bucks to make it with radio shack parts.

depending on the configuration of the Geo sender unit , and mounting flange- and the 51 sender maybe you could blend the two so the 51 sender mounts to the Geo tank. Some careful bending of the 51 float rod will make it accurate in the Geo tank.

I hope you don't have to drop the tank to gain access, I put an access panel in the rear floor on the one I did. Sender was In and out at least a dozen times.

 

Early GM gauges (pre '65) were 0 Ohms Empty and 60 Ohms Full
Late GM gauges are 0 Ohms Empty and 90 Ohms Full

Since the GEO was built by either Isuzu or Suzuki the sender you have is probably way off... You could remove it and test it to see what its resistance is. I've never messed with one. You might get lucky. Most likely you will have to get an early sender to work with your existing gauge.

I sell the $ 3.00 diodes on Ebay and in our eCrater web store for dropping the voltage... Sold thousands of them with no complaints. Least expensive way I've found to do it.

Al

 

Try Rock Valley Auto or Tanks, I bought a adjustable sending unit for a 46' Pontiac (6volt) didn't have to change anything.

 

The older guages and senders were 30 ohms. Any 30 ohm sender will work. As far as the Runtz is concerned - while it's not a bad idea there are many over on the Stovebolt pages that simply run their old stock setups on 12 volts. Some have had theirs running this way since the 70's with no problems. There's such small currents involved (down in the milliamp range) that even doubling the voltage to the guage has no harmful effects on it.

 

Pre 64 GM stuff was 0-30 ohms. 64 and later is 0-90 ohms.

 

I would think any NAPA worth its salt could order you one..
but than again, now a days one never knows

 

That would be correct... Sometimes I type faster than I think and as I get older the thinking gets harder.....

Al