Gooner

Hey Guys,

Almost have the new speedhut gauges wired in. My last missing piece is the fuel gauge. Can I simply splice into the wires in the stock cluster, or do I need to splice further back by the fuel tank? If the first one will fly, which wires do what on the stock gauge for a 1971 Cutlass?

Thanks!

jaunty75

The stock fuel gauge is just an ohmmeter, and the sending unit in the tank is just a variable resistor. The gauge at the dash would have two wires coming off of it. One goes to ground (or maybe it's just grounded through the printed circuit), and the other goes across the length of the car to the fuel tank sending unit at the rear. The other side of the sending unit is grounded, also, to complete the circuit.

If your aftermarket gauge works the same way, I assume it would have two wires coming out of it. One goes to ground, and the other connects to the wire coming from the sending unit. Does your new gauge have instructions?

m371961

Is that correct? One wire is hot from the gauge feed, the other to the sender and the guage measures the resistance, (ohms) to ground. Not sure on the 71, but to be accurate the gauge must be made for the sender resistance. My 65 sender is 90 onms.

jaunty75

Actually, I'm not quite correct! I forgot that power has to come from somewhere! One wire from the gauge goes to battery+ and the other goes to the sending unit. The circuit is completed through the battery ground side.

As far as resistance, yes, I believe your sending unit is 0-90 ohms. Your gauge needs to be the same. What do the instructions that came with your new gauge say, if anything?

Gooner

My gauge has instructions and a very long cable that is clearly meant to reach all the way to the fuel tank. But... I'd prefer to just splice it to the existing wiring to avoid running extras. So the question is which wire to the original gauge is the one my gauge needs to be "hot". My gauge has a black and white wire.

Thanks.

jaunty75

I presume you mean that your new gauge has the black and white wires?

I think this is when having the wiring diagram from the '71 chassis service manual would come in handy. I don't have the '71, but I have the '73. For Cutlass, it shows that the two wires coming off the gauge are pink and tan, with the pink wire getting the 12-volt power from the fuse panel and the tan wire going to the sending unit at the rear of the car.

The '71 service manual is available at wildaboutcars.com, but the scan of the wiring diagram is not the greatest in terms of clarity. Nonetheless, it shows that the colors of the two wires coming from the gauge are the same. Pink to +12 volts, tan to the sending unit.

As far as black and white wires, typically black is hot and white is neutral or return, at least in house wiring, so I would assume that white goes to the sending unit, black to +12 volt power.

RandyS

What does house wiring have to do with car wiring? With cars, black is almost always ground.

Gooner

After looking at the instructions for the Speedhut gauges, it indicates that white will go to the fuel sender source (tan wire in the stock cluster according to previous responses) and black to fuel sender ground or chassis ground. So final question then... where is the best grounding point in the dash. Is there a ground wire in the existing gauge wiring harness to use?

Thanks again for all the help... still the most useful site I've found!

oldcutlass

Yes you can splice into pink power wire the tan wire from the tank. The gauge needs key switched power and the feed from the sender. Anything that is structurally metal is a ground.

Gooner

Just want to clarify... you are saying I can connect the new gauges black ground wire to the pink power wire for the original gauge? New to wiring, but that sounds a little odd. But if that is the way to do it... why not!?

Gooner

Power for the speedhut multi gauge comes from one ignition hot source, so each of the gauges doesn't need it's own power... just one power for the whole quad gauge. But the fuel gauge is unique in that it needs the source from the tank as well as it's own ground. So finding that ground is the last piece of the puzzle! Pretty excited to almost have these things up and running!

RandyS

Often there is a usuable screw or small bolt on the steering column mount, but as mentioned, anywhere on metal under the dash will give you a ground.

oldcutlass

No connecting the ground to the pink wire will result in a short. Can you post a link or a copy of your gauge wiring diagram. So we know what you are looking at.

Gooner

The diagram is pretty hard to read unfortunately. For the 1971 Cutlass it seems there is a pink wire which I am assuming is to power the fuel gauge and the lights. The tan is the sender wire. So I need to connect my new gauges white wire to the tan, and the black ground wire to a grounding post in the dash area. Hopefully that will work!

oldcutlass

Sounds correct to me.

Gooner

Sure enough it works great now! Set the gauge to read 90ohm and it is spot on level now.

However, now that all the gauges are wired and working, I have a new issue. When I turn on the blinkers the new gauge indicators light up perfect... BUT, the volt meter swings 5 volts down in perfect time with the blinker. Also the lighting in my speedo needle dims a bit in time with the blinker as well.

I have everything temporarily wired right now, with all gauge power wiring going into the pink pinout from the old fuel gauge/idiot light and utilizing the ground strap (correct term in this cluster?) that the original gauges grounded to. Also, when I hit the high beams now the stereo cuts off and then comes back on. Didn't do that before with stock gauges.

Ideas?

Gooner

Does anyone think it might be wiser to hook it all to an independent IGN source and an independent ground?

RandyS

I would recommend Yes on both, +12v in Run position, and a solid ground.

Gooner

I bought a Painless Aux Fuse Block for just that purpose. Going to run all gauges and stereo off of that, with it tied directly to the battery.

RandyS

I wouldn't wire anything directly to the battery as your stereo and the gauges will slowly drain your battery. Hook the fuse block to the ignition switch so that it has power in the 'Run' position. I would leave the Stereo hooked to the 'radio' circuit so that you can run it with the switch in the 'Acc' position also.

oldcutlass

It depends on how much power the stereo is pulling. I would hook your aux fuse box to the battery with a relay to power it on with the key. Gauge lighting needs to be connected to the gray wires. Find a different source for your volt meter if it's fluctuating a lot with the blinkers on.