Okay, well i've done read about the whole rewiring and i just plain and simple don't want to do that lol.

Okay, so after market tach it is. Any idea what goes into wiring one up?

 

You need a hot wire that's on with the key.
And you need a wire from the tach test lead from the coil.
and then a ground wire.

Each manufacture of aftermarket tachs are different so you should follow their directions.

 

Cool, thats pretty simple.

Anyone have tachs that their are partial too that seem too have fairly accurate readings and look good? A good price is always in mind too .

 

Another quick question for ya'll. Can i swap a speedo with a trip odo on it with my one w/out a trip odo?
Thanks

 

Yes, but you'll need the clear, plastic shield with the trip meter reset button in it.

 

Awesome thanks.

 

What about taking a truck that came with idiot lights, getting a cluster with tach and full gauges, transferring your idiot lights into the full cluster, and transferring the larger electric connector onto your existing wiring? You would have a bunch of unused pins in the connector, but no real rewiring, and you would get the tach and maintain the idiot lights. Would the full gauges printed circuit support the use of idiot lights if re-pinned? I would ignore the printed circuit connections for the tach and just hard-wire it.

 

This would be difficult to do and would involve some mods...

- The printed circuits are not interchangeable between plastic bodies, I think you'd pretty
much have to somehow use the PCB (printed circuit board) & body from the one with
gauges:



And you'd somehow have to transfer the electrical portions:

CLUSTER WITH IDIOT LAMPS


CLUSTER WITH GAUGES



And, notice that conductor thingamabob on the idiot-light cluster, notice how it's
connected to the two leads on the PCB that also feed the idiot lamp.

I read somewhere how it works and it makes sense once you understand it but it's not
intuitively obvious to me, maybe somebody who knows more will explain.

I should mention I at one time did something similar - I installed a cluster with gauges but
got it only partially working. Replacing the connector in the truck's wiring was fairly easy,
I have a factory wiring diagram and that helped A LOT.

When I got to the ammeter, though, and I looked at the wiring diagram and what it would
take to make that work, I simply said "Oy" and decided to do that "later." (I ultimately
replaced the entire harness with one from a truck with gauges.)

Initially, i simply left those two wires unconnected but, after starting the engine, noticed
the alternator wasn't charging the battery.

IIRC the wires were green/red-stripe & red/green-stripe and were uncharacteristically
thicker than the rest.

This is when I discovered that thingamabob on the back of the cluster, it looks to me like
it merely connects the two leads together.

So, that's what I did - I connected the two wires in the truck together with a butt
connector, half expecting smoke & flames on startup but there was none of that, it
seemed to be working and charging the battery but I was nevertheless uncomfortable
with it because I wasn't at all sure what that device was and what the possible
ramifications might be,

Perhaps others more knowledgeable will chime in and explain how that idiot lamp &
charging circuit operate and tell us if I did an unsafe thing. It seemed to work OK and I
left it that way for close to two years but, as mentioned earlier, I eventually found a nice,
unmolested harness from a 1982 (mine is 1981); even though it had an auto tranny & AC
and my truck has neither, that was pretty easy to figure out.

In sum, what you're proposing is much easier said than done.

 

Great post,

That info helps me a bunch. I was thinking of using the full gauge cluster, and transfering the necessary larger connector onto the wiring in the dash. I would then hard wire the tach in, and very carefully cut away the part of the printed circuit that feeds the ammeter and oil gauges (or at least get it out of the way) With that done, I could drill holes for the 2 idiot lights, and use push-in bulb holders with pigtails, and use wire taps to connect them to the appropriate wires in the harness without hacking it up. It sounds like a bunch of work I know, but all you really have to do is drill 2 holes, swap connectors, and place the idiot lights where the ammeter and oil guages were. My thinking is to inore the printed circuit where there is a problem, and find a way to hard-wire it without hacking up the dash harness (wire taps). As long as you don't expose any runs in the PC that will still be in use, cutting it shouldn't be too big a deal. What do you think?

 

Quote:

Originally Posted by masseysbronco

I was thinking of using the full gauge cluster, and transfering the necessary larger connector onto the wiring in the dash.

This part is fairly easy but I seem to recall some questions coming up when
wire colors from the two connectors weren't the same but, again, the factory
wiring diagram helps a lot.

Quote:

Originally Posted by masseysbronco

I would then hard wire the tach in, and very carefully cut away the part of the printed circuit that feeds the ammeter and oil gauges (or at least get it out of the way)

Hard-wiring the tach is pretty easy, I kinda-sorta did that in that my under-
hood wiring didn't have wires in the harness (esp. leading to inside the cab)
for a tach. I had gotten the correct harness from a JY that's used between the
DSII box & coil so the only thing I had to make myself were the wires leading
from that harness to the tach in the cluster. IIRC I used the PCB & wires
already in the full-gauge connector, this worked pretty well.

For the oil pressure, instead of trying to make it an idiot light, why not just
replace the sensor on the engine with one for a gauge? That will give you a
fully-working oil pressure gauge (well, as well as factory gauges seem to
work), you can use the existing wires in your truck and not have to hack
anything up.

Oil pressure I *think* is white/red stripe while water temp is red/white stripe.

Or, they're reversed, I really don't remember but you can figure it out.

At that point, the hardest thing to deal with is the battery light and that dang
conductor thingy, I really hope somebody who knows more about that device
will chime in and explain.

I will have to look at the insides of the idiot-light cluster and compare against
the gauges cluster, I really don't remember how Ford kept backlamps from
allowing the idiot lights to light up. IIRC there are self-contained, gauge-like
assemblies that install just like gauges but which have the idiot light in the
back of them instead of a gauge. Dunno, I'll see if I can find out more tonight.

 

Well I found an easy, unconventional way to put a factory tach into a cluster with idiot lights lol. Instead of modifying the cluster or wiring, I modified the tach itself. I removed the circuit board from the back of the tach, and I will remote mount it somewhere else. I then trimmed down the plastic that covers the three studs coming out of the tach. Once I trim down these studs, i'll have three wires going from the tach to wherever I mount the circuit card (not too far away). Then I;ll run the wires from the truck to the circuit card. It will be a few days before I get a chance to get inside the dash again, but by trimming down the tach there should be plenty of depth inside the idiot light cluster for it to fit.

 

I'll try and explain it in laymans terms. But even then it may be hard to wrap your head around.

What that metal conductor is on the idiot lamp cluster, is in fact a 500 ohm "bypass resistor" used as a shunt to bypass the altenator idiot lamp.

The Red/Light Green wire comes from the ignition switch, goes to the instrument cluster where it goes through the "Conductor" and altenator warning indicator lamp, then continues to the voltage regulator to tell the voltage regulator that the ignition switch is on. Without the "Conductor" in place, if the bulb burns out, the connection is lost therfore the altenator won't charge. Also without the "conductor" the lamp will be on constantly as the power goes from the ignition switch to the voltage regulator through the bulb. The bulb would never go out.

Electricity takes the path of least resistance. When the altenator is charging, there are several resistors, variable switches, one way diodes, etc... in the regulator that operate. The regulator not only changes the variables of current flow to the Battery, it changes it on the Light Green/Red stripe wire as well, the light green/Red stripe wire has several variable grounds in the regulator and different circut paths. The regulator can still get a power signal from the ignition switch, without turning the lamp on because the current flow is low, therfore it can all go through the 500 ohm "bypass". Thus keeping the bulb out as there is not enough current flow to light it, but still enough to tell the voltage regulator the ignition switch is on.

It works simular to how a fuel gauge works in theory. The more fuel, the less resistance on the variable resistor in the sending unit, that equals less resistance to ground, more current flow, therfore a higher gauge reading. The less fuel, the more resistance on the variable resistor, the more resistance to ground, the lower the gauge.

When the altenator malfunctions, no longer getting the stator voltage signal, the voltage regulator, "switches" the light green/red wires voltage path in the regulator, this increases the path to ground, which causes voltage to be increased on the wire. It becomes too great, and the 500 ohm "bypass" will only alow so much, now current has to take another path, through the altenator indicator bulb. The light comes on.

Does that make any sense?

 

Makes since, I figured it was some type of resistor. I'm fully commited to my alternative plan now though. Most of the plastic on the back of these tachs is just filler so that it would reach the back of the correct cluster.

 

Quote:

Originally Posted by 81-F-150-Explorer

Does that make any sense?

After reading it a few times it's more clear, yeah, but I still only understand it in
general terms and would have to think about it to figure out what to test and
where if I were to try and diagnose a problem in the area.

So, it looks like I didn't do anything dangerous by connecting those wires with a
butt connector, right?

Another question, how much resistance is offered by one of those bulbs?

BTW, thanks for reading it & responding.

Massey: Take pix along the way and post 'em when you're finished, others here
are likely gonna want to do something similar.

 

Correct, they were already connected through the bulb, and through the 500 ohm "bypass"

I tested one 194 bulb with my DVOM, and it gave me a reading of 0.35 Ohms.

Not much resistance at all, but it seems it is enough to keep the bulb from lighting, or I should say, not bright enough to be noticed by the driver. I bet you could take the covers off the cluster and look at the bulb with it running and see a faint glow from the bulb, in the dark.

No problem. It's all in the wiring diagrams, but you have to know what each symbol means. -v^v^v^v- with the "v"s connected in a wire means resistor on the diagrams etc...

I was going to suggest that too.