Oil Pressure Gauge

[custodian]

I have a 73 C10 with the mechanical oil pressure gauge, and I want to switch to an electrical gauge. My wire harness doesn't support the electrical oil gauge, so can I wire the electrical gauge directly to the sending unit?

 

[Bextreme04]

Yes. It is just the single signal wire from the gauge to the sending unit and power goes to the Gauge. You will need a later model electrical gauge though.

 

[custodian]

Yes. It is just the single signal wire from the gauge to the sending unit and power goes to the Gauge. You will need a later model electrical gauge though.

Thanks. I was thinking around an 85 gauge and sender.

 

[Bextreme04]

Thanks. I was thinking around an 85 gauge and sender.

I might have one you can have, I am putting together my electric speedo cluster with tach for the swap and I think I might have an extra electric oil pressure gauge between the three parts clusters I ended up with.

 

[custodian]

I might have one you can have, I am putting together my electric speedo cluster with tach for the swap and I think I might have an extra electric oil pressure gauge between the three parts clusters I ended up with.

Just let me know. I can pay you for it.

 

[dvdswan]

Just remember the 85 gauge will not have the same printed design as your 73.

 

[custodian]

Just remember the 85 gauge will not have the same printed design as your 73.

Yes I know. The speedometer is from an 95 G10 with an 85ish speedometer face plate, so another missed matched gauge will not matter, looking at also changing from a Amp gauge to a Volt gauge, and I know you can't use the same wires from the Amp to Volts, will have to straight wire the Volt meter too. All this is for the LS swap. Might look into digital later, but for now will use what I have or can get.

 

[75gmck25]

I did the amp to voltmeter switch on my '75, and all the wires you need are in the gauge panel. It already has a 12 volt feed and ground for all the other gauges, so you just use that for the voltage reading. Then disconnect the fuses under the hood for the original ammeter shunt wiring. I found a short article on the internet that explained the rewiring.

 

[custodian]

I did the amp to voltmeter switch on my '75, and all the wires you need are in the gauge panel. It already has a 12 volt feed and ground for all the other gauges, so you just use that for the voltage reading. Then disconnect the fuses under the hood for the original ammeter shunt wiring. I found a short article on the internet that explained the rewiring.

I found this article on switching from amp to volt meter.

http://www.73-87chevytrucks.com/techinfo/Electrical/73C10AmmeterToVoltGaugeSwapR1-0.pdf

 

[custodian]

Can someone tell me the oil pressure gauge pin connections looking at the "BACK" of the gauge. Which is the power and which is the sending wire connection across the resistor?

 

[Raider L]

@75gmck25,

Don't ask me why, it's just one of those things I didn't do due to laziness, I guess, but I have an Autometer Amp gauge and a volt gauge. What I did was hooked the Amp gauge up to the original wiring that was in the truck. It didn't work even though its just like the Autometer instructions indicate to do, but even my original Amp gauge didn't work. the fuses are all good and there is continuity in the wires. The Volt meter I did the same and it's fine. So, all these years I've left it in there not working, that's the lazy part I mentioned. The Amp gauge is important if you want to know the condition of the battery and whether it's taking a charge from the alt..
I'm reading your post about taking the fuses out of the Amp gauge wiring, and I lack good electrical understanding most ways except the most basic, where you say something about finding a good article on the internet. I have detailed instructions from Autometer on how to hook the Amp gauge up, what did the article say about using the factory wiring for the Amp gauge? One of the reason's I've done nothing is because there is nothing more I can do to get it to work. Could it be a bad gauge? Probably not, it's a Autometer gauge. If I could fix the original wiring so it would work, problem solved.
Any ideas?

 

[75gmck25]

I have an old multimeter that uses a short piece of flat brass as a shunt when you measure the amps flow. You put the shunt in-line with the charge wire, and the gauge measures the voltage drop across the shunt (which has a known resistance) when the alternator is charging. That voltage drop measurement is used to estimate the amps that are flowing through the shunt. This allows me to measure high amperage that would burn up the meter if run through it directly.

The old squarebody ammeters employ the same concept, except they use a section of the wiring loom as a shunt with a known resistance. However, as the truck gets older the wiring deteriorates and the resistance does not stay the same. The gauge is also measuring very small voltage changes and “calculating” the amps, so it’s not that exact in the first place.

The shunt-based setup is much safer than old 1950’s and 1960’s in-dash ammeters that ran the full amperage flow up to the dash and through the ammeter.

 

[Raider L]

@75gmck25,

Maybe that's the reason why the wiring doesn't work my Autometer Amp gauge. My original wiring goes to the main fuse on the firewall in the engine compartment, what is it called? But the original amp gauge wiring has two 10 amp fuses in line so I thought, "Well, let me try the original wiring." I don't know why I did that because my original amp gauge didn't work either so wouldn't it have made more sense to wire the Autometer gauge like the instructions said, like what you mentioned, it has two #10 wires with one going directly to the positive battery post, and the other to a #10 ignition wire. Those wires go directly to the gauge. No wonder mine doesn't work, I really don't have it hooked up and there's no telluing what is going on with the original wiring. I just didn't do it. No excuse. I was to lazy to do it right, I haven't corrected that yet. I guess I will one of these days.

 

[AuroraGirl]

I have an old multimeter that uses a short piece of flat brass as a shunt when you measure the amps flow. You put the shunt in-line with the charge wire, and the gauge measures the voltage drop across the shunt (which has a known resistance) when the alternator is charging. That voltage drop measurement is used to estimate the amps that are flowing through the shunt. This allows me to measure high amperage that would burn up the meter if run through it directly.

The old squarebody ammeters employ the same concept, except they use a section of the wiring loom as a shunt with a known resistance. However, as the truck gets older the wiring deteriorates and the resistance does not stay the same. The gauge is also measuring very small voltage changes and “calculating” the amps, so it’s not that exact in the first place.

The shunt-based setup is much safer than old 1950’s and 1960’s in-dash ammeters that ran the full amperage flow up to the dash and through the ammeter.

with connections and aluminum wiring..

mmmmm toasty

 

[Raider L]

@75gmck25,

Do you reckon the amps are so low that the gauge can't pick up the signal? Since the gauge is designed to take huge amperage and D.C. voltage and all it's getting is this tiny little trickle of current from the factory wiring? Do you think that there's just not enough there to stimulate the gauge? For it to move? Maybe it is moving but it's so tiny that you can't see it? Ha, ha, wouldn't that be something.