Just do what one of the first guys said. Install a tee and two senders. one for the dash gauge and one for the engine bay gauge. forget all the diode and switching crap. Keep it simple! Ya don't have to re-invent the system.

sidenote?: what amazes me is almost no one has a vacuum guage mounted in the car (to read under load conditions) to tell if the motor is at it's best just with a glance....what is the carb Hg WOT, what is the Hg on a downshift (rings and valves seal under load)

can't resist it...!!!!
Doc' hates it when I over simplify.....why a diode for analog (V or ma) = works just like a check valve, the diode allows flow in only one direction.....so it does matter where it is used

I did not want to do it with two senders cause I am installing an oil temp gauge too. This would give me three senders off the same oil hole. Look like a Christmas tree and secondly the wieght of the three and the movement of the motor might cause a stress problem. Also there is not a lot of clearance between the SBC and the firewall.

I had installed a vacuum gauge from page 1 "So far I got a vacuum gauge on the block, behind the alt..., ". But I had done this because I had a problem with the timing on the old motor, a 305. Instead of the timing reading 8 degrees advance at idle and it running smooth the timing had to be set at 38 degrees advanced and it ran fairly well. Anyway the mech. said the best way to time it is to set the timing so the vacuum gauge is pulling the most vacuum. Anyway the new motor the timing light works fine for it.

To go along with plan A:

Can one use a spare diode-trio from an alternator to hook up two fuel gauges to one resistor wire going to the fuel tank? It will make the installation look cleaner. Or that alt diode is too much for a small 0-90 Ohm gauge?

Thanks!

2000jack,
don't want to side track this thread but a motor is a suction pump, if it was sucking 20Hg at 60mph on a level road and now it sucks 17Hg at 60mph on a level road...you can't feel it while driving......guage tells you to check for the cause...maybe just a vacuum hose leak or connection to get back to best power/mpg

just one example of many for having a vac guage in the car

and it is a great "watchdog" for how heavy are you on the $$$ gas pedal ("try" not to go below about 12hg...depends on the HP, weight and gears)

I don't think an oil temp sensor will fit in the small port for the oil pressure gauge. The oil temp sensor will need to be in an area of flowing oil, such as the line to or from an oil cooler or directly in the oil pan. There is more than enough room to install a tee at the pressure port on a small block but not enough to install a temperature sensor. Those things are big.

agree with jolly roger,
oil temp sensor needs flow, (same as the temp sensor in the intake manifold's coolant flow stream)

Doc here,

On a Tach, hook the wires direct..you would not want a diode on the Tach line at all..It would tend to filter or clip the spikes the Tach is supposed to be counting..

My DD Corvette Has Two tachs, a ProComp Monster and the stock Dash Unit..both run fine on the same tap..for the last 4 years.

When I hooked up the second tach, I was surprised to find how "Non-Linear" the stock tach was..a whole bunch of ranges that were 200 to 500 RPM's in error..Which is why I went to the aftermarket unit..I noted it with a hand tach before..



Doc

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Doc here,

Correct.. In this case it provides isolation from one gauge resistance to the other, into a common point (the sender) .

Doc

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Doc here,

I did this ONCE, on a Buick I had in a Toyota..

About every 100 hours of run time, one of the two senders would break at the TEE, or at the bottom of the sender from vibration....shooting oil all over the place..

Or they would also back out and leak from the plumbing vibration and weight.

Anymore, I only run 2 senders if there is a place to mount both in the block..

Doc

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Doc here,

Get a pack of 1N4001's from radio shack..$1.49 for a pack of two..

A Diode trio is configured as a unit inside the brick to rectify raw AC into DC.. (they all are connected to each other either cathode to anode or Visa Versa) And can not be used as a 3 Single diodes (per~Se..)

The 4001's are small (about the size of a resistor) and can be installed on the wire with a sleeve of heat shrink over it..(you'll never notice it..)and a lot cheaper than a Diode trio..

BTW, I have never done this on a Fuel gauge before..although I don't see why it wouldn't work as well..

Doc

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Doc here,

I think it's a good addition to the gauge cluster too..

On mine, It also tells me if my headlight doors and Windshield wiper doors will open and close..(vacuum motors)..

Doc

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Doc, thanks for the reply. I will head to Radio Shack. I have a dual fuel gauge setup as well. The stock one was always out of wack :-) Now I understand why.

darom,
(first, why do you want 2 working gas guages on one tank?)
(one (?) for the mother-in-law in the back seat so she can nag ya "YA NEED GAS!")

if both are already wired to the same tank and new#1 is working correct and factory original #2 is "whacko" readings, much more likely the cause is #2 is broke* and not "calibrating" correctly (my "china" boards comment)

broke*can be = old corroded tank sender and wires=signal too weak? had a short in the car that spiked thru the guage? signal loss in a ECU? can be lots of different causes

best solution: tape a picture of the wife over the original guage! lots of "browny points"! (and cause they want $$$ for a new factory guage!)

if both were reading wrong, then diodes (checkvalves) might work but like doc I've never tried it