mustang sending unit question
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Tuned
Joined: Nov 2006
Posts: 276
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From: washington state
mustang sending unit question
hey there, is there anyone out there that has a solution to make the mustang sending unit work with stock fuel gauge on a 56 ? my needle shoots past "full" and never moves down ward
Laughing Gas
Joined: Feb 2002
Posts: 932
Likes: 9
From: DFW, TX
Have you measured the "full" and "empty" resistances of the Mustang sending unit? If they are the same as the '56 sending unit, it should work. I can't remember the values off the top of my head, but will do some checking and post back when I find them.
Also, the '56 uses a voltage regulator to effectively reduce the operating voltage of the guage to ~6 volts. If you don't have the regulator in the circuit, you will see the guage jump past full, as you described. You can check your guage by hooking up 3 volts (two 1.5 volt batteries in series) across the terminals of the fuel guage. If you have the polarity correct, the guage should show ~1/2 full.
Good Luck!
Also, the '56 uses a voltage regulator to effectively reduce the operating voltage of the guage to ~6 volts. If you don't have the regulator in the circuit, you will see the guage jump past full, as you described. You can check your guage by hooking up 3 volts (two 1.5 volt batteries in series) across the terminals of the fuel guage. If you have the polarity correct, the guage should show ~1/2 full.
Good Luck!
Laughing Gas
Joined: Feb 2002
Posts: 932
Likes: 9
From: DFW, TX
Here's what I found on the sendiing unit resistance. It should measure ~73 ohms with the float in the empty position and ~10 ohms in the full position. According to Autometer, this is standard for Ford products up to 1987, so the Mustang sending unit should work.
Is the instrument cluster wiring original? I would look to see if the instrument voltage reducer is still hooked up on the back of the instrument cluster. It looks like a rectangular metal can with two posts for hooking up wires and the can is grounded to the back of the cluster. Replacements are available from NAPA and others and were common from 56 well into the 70's. Possibly all the way to 87, but I'm not sure there.
Good Luck!
Is the instrument cluster wiring original? I would look to see if the instrument voltage reducer is still hooked up on the back of the instrument cluster. It looks like a rectangular metal can with two posts for hooking up wires and the can is grounded to the back of the cluster. Replacements are available from NAPA and others and were common from 56 well into the 70's. Possibly all the way to 87, but I'm not sure there.
Good Luck!
Laughing Gas
Joined: Feb 2002
Posts: 932
Likes: 9
From: DFW, TX
If you have a multimeter, unhook the wire that goes to sending unit from the back of the fuel guage and read the resistance between that wire and ground. You should get a reading between 73 and 10 ohms. Since your guage is reading past full, it sounds like you may have a hard short to ground on this wire.
While you have the cluster apart, go ahead and check the guage hooking up 3 volts (two 1.5 volt batteries in series) across the terminals. If you have the polarity correct, the guage should show ~1/2 full.
Let us know what you find out.
Good Luck!
While you have the cluster apart, go ahead and check the guage hooking up 3 volts (two 1.5 volt batteries in series) across the terminals. If you have the polarity correct, the guage should show ~1/2 full.
Let us know what you find out.
Good Luck!
