Gauge Wiring

My gauges never worked, and I've recently rewired the whole truck, so I don't know the answer to this question. Does anyone know what terminal is the positive one (6V!) for the gas gauge? Looking at the gauges from the drivers seat, is it the one towards the driver's door? If so is it the same for the temp gauge? Or just the reverse for both? (I know I have to daisy chain the power line between gauges.)

I've fried one gauge with too much power, but I'd like to not only not repeat that problem (I have a new voltage reducer) I want to make sure I don't commit another blunder.

The gauge wiring diagram I have shows the 6 volts from the "constant voltage unit" goes to the passenger side of the fuel gauge, and from there to the passenger side of the temperature gauge. Carl

see gauge wiring diagram: www.vintage-vans.com/67fordwiring6.html

-it may be more clear at www.vintage-vans.com/67fordwiring4.html Carl

Here is a verbal description of the fuel gauge
wiring I wrote a while back:
https://vintage-vans.forumotion.com/t14006-fuel-gauge-sender-diagnostics

Look at the part about VOLTAGE GOING INTO CVR
(constant voltage regulator) which makes a pulsed
5 volts (on average) source.
"Incoming is a SINGLE Blk/Grn wire, outgoing is a
single B/G wire that splits into a double B/G
wire for both Temp and Fuel."

B/G stands for Black with a Green Stripe,

Not sure if this helps any,
Good Luck,
George

Thanks Carl and SD! I looked at your links and still have a couple of questions.

1. Regarding the voltage reducer, my original wiring is gone, so I want to be sure the 12V line from the fuse box goes into the correct terminal. (Looks like from Carl's diagram the incoming line should go in the drivers door side of the regulator and the passenger side goes to the gauge.) I can hook it up and test it but call me gun shy - I don't want to fry a new unit if hooking things up backward is a no-no.

2. SD, Your write up was excellent however the following section confused me a little:
"TEST THE WIRE GOING TO THE GAS TANK
Assuming the Fuel Gauge is connected and the Gauge Cluster is re-installed in the Dash:
Pull the wire off the Fuel Sender Unit and ground this wire to nearby clean metal. Momentarily
turn IGN to "on." Fuel Gauge will quickly go to Full. (Shut down quickly after verifying gauge
function. The gauge is supposed to handle 5 volts not 12+.) Note: NEVER connect 12V to the
Sender as some sort of test, it will fry. If the gauge went to "FULL" then the wiring from the
dash to the tank is good..."

Are you talking about the line from the sending unit to the gauge? If so, how does the gauge register if the line from the tank is disconnected and grounded? (Or is grounding it somehow completing a circuit to the gauge through the gauge cluster?)

Sorry for the basic questions. I'm double checking the grounds, especially at the tank, but I think they are all solid. (New sending unit and new wire from the sending unit to the dash.)

Jeff, which voltage reducer did you end up with? Reason I ask is some are rated at 1-4 and 6 amp and are for 1 gauge only. All the ones I have used have a + or B or IGN stamped on it close to the stud for 12 volt supply line. Of course the other stud goes to the gauge or gauges. As SD explained(a very superb explanation I might add)there must be a good ground at the tank. Some have used rubber in between the straps and tank to reduce rusting there and lose the ground. By removing the sending unit wire and touching it to metal will ground the gauge(it will show Full) to test if the gauge is any good(remember to do this after everything is hooked back up) Hope this helps!

OG

Hey Jeff,

You are onto it: "Or is grounding it somehow completing a
circuit to the gauge through the gauge cluster?"

Hard to visualize this type of circuit. Two things are
worthy of mentioning. First, there is just one wire going
to the gauge, and the ground/return "wire" is merely the
tank/body/dash/ cluster metal itself. Second, the gauge
can be affected by the voltage of the entire body (ie.
grounding the wire from the gauge-to-sender at the sender
end, to the body.) That would be like a full tank on the
sender unit.

You can momentarily hit your gauges with 12 volts, BUT I
emphasize MOMENTARILY, as the gauge reaches "full" or "hot"
you better shut off the juice to the gauges! They handle
5 volts just fine +/- a couple volts.

I recommend doing the battery test I described, using "AA"
batteries, NOT the van's battery, on your gauges, as it
builds confidence.

Sounds like you just need to sort out the wire from keyed power
(fuse block) connecting it to the CVR (constant
voltage regulator) and having two wires come from that to
your Temp and Fuel gauges. Metal contact of the two gauges
to the metal dash completes their electrical connection.
Varying the resistance in that circuit (rheostat in the
fuel sender) will change the constant voltage going through
the fuel gauge, thus making the pointer/needle change
position. Whew!

Please ask more questions on this, as I can imagine how
frustrating it would be to accidently wreck a gauge or two.
(Don't ask me how I know! HA HA)

George

Oh, one last thing: I cannot emphasize how important it is
to properly ground the ENTIRE vehicle- These old cars live/die
by this. I've seen so many missing one of the ground links.
Usually the ground from the block to the body is missing. And
be sure this ground is at the opposite end of the motor from
the other ground going to the block, as this seems to make a bit
of difference too. I wrote about the ground paths in that write
up.

Got home late tonight, so haven't had a chance to do anything today. The voltage reducer I bought is the correct replacement. It just came today and I notice it has two spades on what should be the low voltage side and the incoming side has the kind of female spade connection I think is correct for that side.

SD, Thank you so much for your further explanation. I'm starting to grasp what you've been saying and will proceed accordingly. I have a voltage tester and I'm starting to understand how this all works. (The light really came on with your explanation of the rheostat in the fuel sender unit!)

Just waiting on the new (to me)gauges get here...