79 Ford truck instrument harness wiring guide
#16
11-21-2016, 09:13 AM
I'm working on a 79 F250 ranger right now for a guy. I need to know if these wires are going to be the same. Most of the colors are the same but I'm getting nothing but the gauge lights. I'm not getting any fuel pump reading, signals, or high indicator. The truck was in a field and all the wireing was toast. The truck has been mostly restored and a painless wiring harness mostly installed. I'm only haveing trouble with the gauges. The gauges are the ones that were in the truck when it was bough. I'm also unsure how to wire up the amp meter. Suggestions and help are all welcome.
The fuel gauge works through a ground. The gauge "sees" voltage coming in, the ground circuit goes to the tank where it runs through a variable resistor (sending unit) and then to ground.
If the gauge doesn't work at all, with the ignition "on" ground the wire that goes to the sending unit. If the gauge and wiring are okay, the gauge should swing over to "full". If it does, then either the sending unit is bad or the ground connection is bad.
If the gauge doesn't move when grounded, the first thing to do is check for voltage at the gauge. These gauges operate on reduced voltage ~5.5 volts. The ICVR (instrument cluster voltage regulator) is on the back of the instrument cluster. It's a little box that has what looks like a 9V battery connection. If you have voltage then either the gauge or the wiring to the sending unit would be suspect.
I don't know how much good it will do because you're installing a Painless wiring harness, but here is a link to the '79 factory wiring diagrams.
BTW, welcome to FTE, lots of good people here.
1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net
#17
03-18-2023, 04:46 PM
The factory ammeter is tricky. It is not a direct read type of meter. It is a shunt style meter. There is a shunt wired into the alternator wiring harness that senses the output of the alternator. This signal is sent to the ammeter and that is what the gauge sees.
The fuel gauge works through a ground. The gauge "sees" voltage coming in, the ground circuit goes to the tank where it runs through a variable resistor (sending unit) and then to ground.
If the gauge doesn't work at all, with the ignition "on" ground the wire that goes to the sending unit. If the gauge and wiring are okay, the gauge should swing over to "full". If it does, then either the sending unit is bad or the ground connection is bad.
If the gauge doesn't move when grounded, the first thing to do is check for voltage at the gauge. These gauges operate on reduced voltage ~5.5 volts. The ICVR (instrument cluster voltage regulator) is on the back of the instrument cluster. It's a little box that has what looks like a 9V battery connection. If you have voltage then either the gauge or the wiring to the sending unit would be suspect.
I don't know how much good it will do because you're installing a Painless wiring harness, but here is a link to the '79 factory wiring diagrams.
BTW, welcome to FTE, lots of good people here.
1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net
The fuel gauge works through a ground. The gauge "sees" voltage coming in, the ground circuit goes to the tank where it runs through a variable resistor (sending unit) and then to ground.
If the gauge doesn't work at all, with the ignition "on" ground the wire that goes to the sending unit. If the gauge and wiring are okay, the gauge should swing over to "full". If it does, then either the sending unit is bad or the ground connection is bad.
If the gauge doesn't move when grounded, the first thing to do is check for voltage at the gauge. These gauges operate on reduced voltage ~5.5 volts. The ICVR (instrument cluster voltage regulator) is on the back of the instrument cluster. It's a little box that has what looks like a 9V battery connection. If you have voltage then either the gauge or the wiring to the sending unit would be suspect.
I don't know how much good it will do because you're installing a Painless wiring harness, but here is a link to the '79 factory wiring diagrams.
BTW, welcome to FTE, lots of good people here.
1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net
I grounded the # 15 Orange wire at the cluster harness (fuel gauge sender harness wire) and the gauge goes to 3/4 full. ( so the gauge is working--not sure how accurate). I'm also showing 5.8 volts coming from the voltage regulator (VTR) at the back of the fuel gauge which is correct.. Does this point to bad wiring or a sending unit or either? I remember I did clean the ground coming from the tank previously but I can't get to the connection on the tank. Also there is a pigtail connector on the hot wire to the sending unit so I was thinking about disconnecting that and running a new wire up to the cluster. Question is can I run that right to the orange wire connector on the cluster? Just trying to check what I can without dropping the tank,Ugh. Thanks anybody that can respond. Dennis
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