low fuel relay

[js29no]

i am in need of a low fuel relay part # 2983828 it's for a 1970-71, gran coupe,or challenger S/E modals   thanks.

[johns cuda shop]

I remember when I had my Grande Coupe I sourced one from a 70 Fury Grande Coupe..

[1 Wild R/T]

They were the same in lots of B & C bodies, trouble is it wasn't a  common option, all body styles are getting harder to find & it's a 45+ year old electrical part... I couldn't find a good used one back in the eighties... Might be better off just to pay the price for an NOS one....

Doubt this is right but it's the right pt number....   
http://relay.dvautoparts.com/discount-store/1970-1971-1972-1973-cuda-challenger-full-w-jkjmqrmjjjjl

Heres the I gotta have it price...
http://www.hiltopautoparts.com/product/nos-mopar-low-fuel-relay-1970-1-plymouth-dodge-e-body-cuda-challenger/

This guy shows one in stock....
Owner:  Jack Koziol
Email:   Sales@cjmotorparts.com
Phone:  (732) 446-3738
Fax:  (732) 446-0486





This may help... Unfortunately RTE is out of business


Theory of operation:

+12V Power us fed into the IGN and COM terminal when the key is turned on.
Vehicle Ground is connected to the GND terminal through the case of the relay.
The GAGE terminal is connected to the fuel gauge, where the limiter would be connected in a normal car that did not have a low fuel feature.
The other side of the fuel gauge is connected to the standard Mopar fuel sending unit, same as in any mopar. The fuel sending unit will have a resistance of approximately 10 Ohms when full and approximately 80 ohms when empty.
The LAMP terminal is connected to the low fuel light lamp.
There is a coil of magnet wire between the IGN terminal and the interior point labeled X that is about 6 Ohms. The resistance of the X coil, the middle heater, the resistance in the fuel gauge, and the sending unit resistance all add up to control the amount of current going through the middle heater coil when the limiter is in its on state.
The X terminal feeds voltage into the middle heater coil when the top bi-metallic strip (limiter) is closed, when tends to open the bottom points. When the bottom points are open, then the low fuel light is off. The fuel sending unit being at full (10 Ohms) means that a lot of current goes through the middle heater strip, keeping the bottom bi-metallic strip strongly open. Note that the middle heater strip is only on when the voltage limiter is on.
The top bi-metallic strip is in fact a voltage limiter, just like the limiter on the back of your dash. The only difference between the standard voltage limiter and the limiter inside this relay is that this limiter is set to stay on longer to compensate for the voltage loss in the X coil and the middle heater strip. In other words, it is set to deliver the same amount of power to the fuel gauge as a standard limiter would, even though there is the added resistance of the X coil and the middle heater strip.
The bottom bi-metallic strip is a latching relay. It is open when there is enough average current in the middle heater coil to make it stay open. The current in the middle heater coil is controlled by the fuel sending unit resistance. When the fuel sending unit resistance gets high enough so that the middle heater coil allows the bottom strip to close, then the bottom bi-matallic strip feeds power to the LAMP terminal through the bottom heater. When the LAMP is lit, this causes the bottom heater strip to heat up which tends to force the bottom bi-metallic strip to stay closed, acting as a hysteresis element. This is needed to make sure the low fuel relay won't open and close as the limiter turns on and off.
There is a small amount of voltage loss in the bottom heater strip, which will cause the low fuel light to be slightly dimmer than all the other bulbs in the car. This bulb is a standard 14.4 Volt bulb, number 1892-USA part number. The resistance of this bulb is important in that it helps set the current in the bottom heater coil. The resistance of the lamp is listed as 120 Ohms (cold?). The resistance of the bottom heater when cold is about 1 Ohm.
RTE will eventually make a replacement circuit board for this relay for all those people out there who need a new relay, or who would just like to add a low fuel light to you car. When we make this board, we will make it so that it can go into the original low fuel relay metal can, and we will also have some 4-40 holes in the board so that those of you without the relay metal can will be able to mount the board under the dash.

[JayBee]

I wasn't going to chime in until mine were tested but I didn't want to see you spend outrages money either. Anyway I've got these two and will try and get around to figuring out how to test them this weekend. I just printed out Wild's post and found some other info from Googling. Hang in there until after the weekend then, if they test out okay, we can figure something out.

[js29no]

i called jack koziol and he had an NOS relay in stock, about the time you were posting i was at the post office jaybee. but i do appreciate that! now i need to see how it is wired reading the theory wild posted i don't use the limiter  on the back of the cluster i use the relay instead? the wiring diagram i have only covers the over head console it's self and not behind the dash. any info on that will be much appreciated. and thank you wild that helped a lot.

[EB3-GranCoupe]

Great info on Relay operation. Thanks!!

[Slotts]

Hey John,

I cheated with a variable speed wiper switch. 

http://s248.photobucket.com/user/Slotts/media/Low%20Fuel%20Relay/IMG_0613_zpsf52ef8ee.mp4.html?sort=3&o=7

Jim

[1 Wild R/T]

Schematics

[JayBee]

Hey John,

I cheated with a variable speed wiper switch. 

http://s248.photobucket.com/user/Slotts/media/Low%20Fuel%20Relay/IMG_0613_zpsf52ef8ee.mp4.html?sort=3&o=7

Jim

Hi Jim. I found that video after googling "low fuel relay", what a coincidence - EH. I used a spare sending unit rheostat and they both worked,  sort of. Very slow to react. Also I smoked one of mine by trying a different bulb. I'll try to solder the burned wire back together. It's the the thin wrapped wire opposite the widest one.

[Slotts]

Hey John,
That is pretty funny, EH? 

If you click on the right > on that video page, you can scroll through still pictures and will see where I removed that wire your are talking about. That was from a client who wanted that to work again a few years ago.  If you look at the video before pressing play, you will see the new wiring and testing it before assembly.

I have to be careful not to mention my company name here or am I soliciting any business. (Right Ross Sr.?)

Jim

[1 Wild R/T]

Whether you can or can't I will..... Jim does fantastic work on rebuilding all sorts of components, he specializes in switches & other electrical components & if you haven't seen his work you should have a look...

http://board.moparts.org/ubbthreads/ubbthreads.php/topics/738678/js-restorations.html

[1 Wild R/T]

Found a more specific schematic....

[EB3-GranCoupe]

Fantastic!,  I forgot what color wire went where, and I didn't feel like ripping my headliner out just to find out all over again.   

[JoeGrapes]

I found a low fuel relay from an AMC car that was cheap at a swap meet. It looks exactly the same so I bought it. When I put it in the low fuel light is on all the time. I took them both apart and found my original one has a small silver cylinder with a red stripe while the AMC one does not. What is it? Could it be to low the voltage to the gauge to 5V because the gauge voltage limiter is no longer in the fuel circuit? Maybe I can figure a way to add a Radio Shack part to the circuit to do the same thing.