Wiring the Temperature & Oil Pressure Senders

[karlos]

Using the Speedhut (classic) gauges with the RF chassis harness. The pigtails that come with the gauges are two-wire (signal and ground), while the chassis harness is one wire (signal only). Since the RF harness already includes wires where I need them behind the dash and in the engine compartment, I'd prefer to utilize them rather than run the additional harnesses that come with the gauges. But what to do about the sensor grounds? Assuming the use of liquid thread sealant rather than Teflon tape, will the sensors be adequately grounded through the threads? Interested to hear what those of you who used the RF harness did to provide a ground path for the sensors.

Thanks as always.

-Karl

[Jeff Kleiner]

The 2 wire Speedhut sensors don't ground through the sensor body threads; they get their ground via the second wire. Two ways of going about it:

1) Mate the RF wire signal wire as well as an added ground wire to the sender underhood.

2) Run the Speedhut pigtail with the encased signal and ground wires back to the dash.

After having done it both ways my preference is #2---I feel it is cleaner, less cluttered and more OEM appearing.

Jeff

[Raceral]

RF does say in their book not to use any type of sealant on the threads.

[DaleG]

These instructions from Jeff helped me:

Jeff Kleiner’s WIRING DIRECTIONS
The Speedhut/FFR Classic gauges use 2 wire senders while the RF harness is set up for one wire so I recommend doing kind of a hybrid that will incorporate the pigtails with the black/white wires. You'll need to power up all of the gauges on their red wire by connecting them to the brown "gauge feed" wire in the harness. Also connect the black "ground" wire in the dash harness to each of the gauges' black wires. You will carry the tachometer signal from the coil on the purple "coil-tach" wire that runs all the way through in the sending units subharness. The speedo signal comes from the trans through the green and gray wires which will join the yellow/red and yellow/black wires on the gauge. Polarity is not important as it is only counting pulses. For the coolant temperature and oil pressure gauges run the long pigtail with the yellow/red and yellow/black wires to their respective senders. Once again polarity is not an issue because these are reading resistance. The voltmeter has no sender, the gauge power and ground give it all it needs. Fuel gauge connects to the light green "gas sender" wire. I recommend powering the clock from the red "radio memory" wire. That will get everything working.

Next move on to gauge lighting. The white wire from all of the gauges connects to the RF harness white "dash lights" wire. If you have the seperate dimmer module the white harness "dash lights" wire connects to the input of the dimmer; the dimmer's black ground connects to the black harness ground. From there the dimmers output snaps into the daisy chain connectors for the lighter gauge wire. It seems redundant but is this way because the needles are lighted independently from the gauge face and are not dimmed. If you do not have the dimmer module then the small white wire at the end of the snap together chain also connects to the harness "dash lights" wire, not directly to the headlight switch. By the way, before you drive yourself crazy thinking something is wrong---the hands on the clock are not lighted.

Good luck,
Jeff

[karlos]

I agree that using the harnesses that came with the gauges will make for a cleaner looking installation. But I'm loath to put more holes in my firewall. So what I think I'll do is connect the gauge harnesses to the sensors and run them back to a point in the engine compartment where I can connect the signal wires to the RF harness that's already there. The RF harness will then dump the signal wires out behind the dash. All that's left to do from there is run the ground wires in the gauge harnesses to a convenient (but hidden) nearby location in the engine compartment. Maybe that's what Jeff meant by hybrid?

Thanks for the help, guys.

-Karl

[Jeff Kleiner]

You don't necessarily need to add more holes in the firewall Karl. Feed the Speedhut jacketed pigtails for coolant temp, oil pressure and oil temp into the harness split loom then break out between the firewall and dash. From there you mate the signal wires to the corresponding gauges and make a common ground. Unless you anticipate repurposing the unused RF temp/pressure wires for accessories they can be removed from the harness.

Jeff

[karlos]

From there you mate the signal wires to the corresponding gauges and make a common ground. Unless you anticipate repurposing the unused RF temp/pressure wires for accessories they can be removed from the harness.

Jeff

Jeff,

In the first image below the yellow/red wire is the signal wire and the yellow/black wire is the ground. I've been trying to understand how the sensor finds a ground path between the sensor and the gauge. Well, my voltmeter tells me there's continuity between the yellow/black wire and the ground wire on the sub-harness that powers the gauge (black wire on the rightmost connector). So it appears the temperature/pressure sensors are grounded through the gauge itself. If I have all that right, then the yellow/black wire is left unconnected when wired as you described above, correct?

Interesting that the Speedhut instructions don't even include a depiction of the sensor ground wire (second image), presumably because grounding takes place through the threads. Confusing.