Restoring Rusty

[Gregski]

what's this, get this book outta here it's in my way, say what flip to page 75...

now maybe I took a moist paper towel and whipped off the white labels off my own fuse box maybe I didn't I'm just sayin'

lets just keep in mind we have this fuse diagram so lets refer to it for the next few exercises

Can you point to the Water Temp Gauge fuse please?

No, ok how about the Oil Pressure fuse?

No, how about the Fuel Gauge?

Sure you must be able to find the Ameter Gauge fuse?

still no...

And that's why we tore this Oreo Cookie outside bulk head connector / inside bulk head connector / fuse box apart! So that we can grasp what is going on

[Gregski]

here is a pic of my '74 bulk head connector, black plastic box on the firewall by the brake booster

wish GM gave us a diagram of these wires like they did above for the Fuse Box, but they don't so we will make our own (we are looking at the diagram standing in front of the truck with the hood open and the bulk head connector on the firewall, not removed) so the big red wire would be in slot number 4.

Ok, so our connections for the gauges are

#3 Ameter

#5 Brake

#9 Water Temp

#11 Ameter

#13 Right Turn Signal

#14 Left Turn Signal

#23 High Beam

#25 Fuel

[Gregski]

OK, so now that I have confused the heck out of everybody, let me walk you through how this works using the Water Temperature Gauge

1. A dark green wire starts on the Water Temp Sending Unit in my driver side cylinder head (located between #1 and #3 spark plugs)

2. It runs inside the engine wire harness to the #9 slot in the black plastic bulk head connector mounted on the outside of the firewall (driver side next to the brake booster)

3. On the inside of the cabin it makes a quick right and bypasses the fuse box, it does NOT connect to the actual fuse panel, and heads straight up to the 18 pin gauge cluster connector where it plugs into the #8 pin on my '74 and will be moved to the #9 pin on the '78 cluster

4. from there it jumps on the Printer Circuit Board super highway where it car pools with pin #9 for ground on my '74 and will use pins #6 & #10 for ground instead when I switch over to the '78 cluster to reach the actual Water Temp Gauge, aka it's final destination

and there you have it a Cradle to the Grave home run (to borrow electricians cable run terminology)

[enaberif]

Holy crap man you are a very busy but oh so much a saint. Having a correct pin out and labelling of that bulkdhead connector is going to help millions! That **** needs to get stickied.

[hatzie]

Reading the wiring diagrams seems overwhelming till you know a few of the secrets...

To read the GM wiring diagrams you need to be able to decode the GM circuit numbers.

There are several pages of GM circuit #s in the front of some of the factory wiring manuals starting in 1977 or 78. The GM circuit #s range from 2 to 831 in the 1978 manual and range into the low thousands in the later manuals.

Many of the circuit #s are for the same function every year. I can't guarantee that they're all the same because certain things were added and dropped so GM might've recycled a few obsolete numbers... like the ammeter that was dropped for the 76 model year and the seat belt buzzer that they added in 75 or 76 and on it goes...

GM labeled each wire in the diagram with { wire gauge/jacket color - circuit # } Some wire numbers have an added letter suffix to the circuit # that identifies branches before and after a splice at a component or mid harness.

Once you know how to read the wire codes it's much easier to read the diagrams because you only need to know generally where the wire goes. You can pick it back up at its' termination point and a new suffix tells you to look for a splice.

For instance;
If you look at the circuit #s at the cluster plug, fuse panel, and bulkhead plugs in the 78 diagrams... each end of the wire is labeled.
You can find each end with just the circuit #.
Example:

1. Ignition power to the cluster is Circuit #39. It's a 18 gauge Pink wire and it splits at a splice into three 20 gauge wires feeding the cluster plug.
   [**]At the fuse panel it's labeled { 18PNK - 39A } At the cluster plug you find three wires labeled { 20PNK - 39E, 20PNK - 39F, and 20PNK - 39G }
   [**]In the middle of the wires is a DOT labeled "39" that denotes the splice from the 18gauge wire to several 20 gauge wires.
2. The dash grounds are pretty much the same deal... Cab Grounds are Circuit #150. The main ground is tied to the odd copper buss bar or a ring terminal on the E-brake pedal bracket.
   [**]It's labeled { 18BLK - 150A } and the grounds at the cluster plug are labeled { 20BLK - 150E, 20BLK - 150G, and 20BLK - 150H }
   [**]In the middle of the wires is a DOT labeled "150" that denotes the splice from the 18gauge wire to several 20 gauge wires.

If you look at the bulkhead plugs the cavities are all numbered with GM circuit #s. The cluster plugs are done exactly the same way. GM also noted whether you were looking at Wire entry or terminal view of each connector.

The other interesting thing you'll find is each component connector has the Delphi part # or, in the case of ring terminals, the diameter of the rings... The starter and alternator is a good example of that. You'll also see the gauge of the fusible links called out at the starter.

[Gregski]

so after all that, here is where we stand, we need more parts (to do it factory like and not a hack job)

1. Voltmeter wire that runs from the inside bulkhead to the cluster 18 pin connector to pin #4

2. a triple pin pink ignition power wire that runs from the inside bulkhead block to pins #4, #6, and #16

3. a triple pin black ground wire that runs from the inside bulkhead block to pins #3, #8, and #10

4. a spikey 6 prong ground bracket to accomodate the Tachometer stand alone wiring harness ground

5. need to buy a small fuel gauge

however I am enjoying this project immensely and having fun figuring things out, feel much more comfortable now if I was to troubleshoot something electrical

[Gregski]

yes I did get this Geeky with the printed circuit board 18 pin connector, whacha gonna do about it, tell my wife I stole all her quetips, hee hee

on a serious note there is an Electric Parts Cleaner (not safe for plastics) and an Electronic Parts Cleaner safer for plastics

[Gregski]

I also wired up the Tach as it does not require the circuit board and comes with it's own wiring harness which on one end plugs in to the HEI distributor and on the other to ground (black wire) and like so to the Ignition spot in the Fuse box with the pink wire

I also connected my old Speedometer (more on why I am using my old Speedo still later) again no need for circuit board for this, it just uses a mechanical twisty turney cable that runs to the transmission on my manual 4 speed

did another Tach test against my timing light and once again it reads way off, no bueno I may bite the bullet and buy a brand new Tach from LMC Truck next month after I get paid (I doubt any old used Tachs work accuratley on eBay)

[Gregski]

Originally Posted by greg64

If you can drive at a known speed (like using a GPS), and we know your tire size and rear gears, we can figure out what RPM the engine is actually turning.

OK, took her for a spin held her steady at 60 MPH and the Tach read approximately 1,900 RPM

Tires are 235/75 R15

Rear Gears - no idea, did the 2 full wheel turns an the drive shaft went around 3 and a bit more than 1/4 turns but not quite 3 and a 1/2 so I am guessing 3.42 gears

so online Calculators say the RPM should have been 2,386 for a manual transmission

[rusty76]

Wow what a write up.!

[greg64]

Originally Posted by Gregski

OK, took her for a spin held her steady at 60 MPH and the Tach read approximately 1,900 RPM

Tires are 235/75 R15

Rear Gears - no idea, did the 2 full wheel turns an the drive shaft went around 3 and a bit more than 1/4 turns but not quite 3 and a 1/2 so I am guessing 3.42 gears

so online Calculators say the RPM should have been 2,386 for a manual transmission

Greg, I got 2388 RPM with your numbers, which agrees with your value. I guess the tach really is off.

Great job on all your wiring. My Haynes manual shows the firewall bulkhead connector and what each wire is numbered. But, like you, I made my own blown up drawing to make things easier.

[bilfman]

Originally Posted by Gregski

I also wired up the Tach as it does not require the circuit board and comes with it's own wiring harness which on one end plugs in to the HEI distributor and on the other to ground (black wire) and like so to the Ignition spot in the Fuse box with the pink wire

I also connected my old Speedometer (more on why I am using my old Speedo still later) again no need for circuit board for this, it just uses a mechanical twisty turney cable that runs to the transmission on my manual 4 speed

did another Tach test against my timing light and once again it reads way off, no bueno I may bite the bullet and buy a brand new Tach from LMC Truck next month after I get paid (I doubt any old used Tachs work accuratley on eBay)

There is a resistor in those tachs that causes them to read wrong. It is a 3 buck part and takes about half hour to fix . A guy has an excellent guide on line to do it. I'll search for the link and post it when I find it. I did my tach several years back, still works perfect!

[bilfman]

Found the tutorial.

http://www.howtoalmanac.com/kevin/pr...ve/tachfix.htm

[Gregski]

Originally Posted by bilfman

Found the tutorial.

http://www.howtoalmanac.com/kevin/pr...ve/tachfix.htm

God that site is horrible to read, thank you for the resource though, also I think all I may need to do is calibrate it, but he does not tell us how to do it

"we still have to calibrate it" he says

"there are multiple ways to do this" ok do tell

"you will need something that will measure frequency. you can either use a frequency generator or use your engine."

engine, got one

"if you use your engine you need some other tachometer to calibrate to"

yep yep got my trusty MSD digital timing light

"and remember to make sure that the tach filter is before the tach or it will blow up"

say what?

so hook up 12 volts to the power pins (bolts).

now hook up your [...] engine tach wire to the signal pin (bolt)

set the frequency of the generator to 100Hz, now adjust the amplitude of the generator until you get a stable RPM measurement on the tach (approx 12-15v).

Now just adjust [...] your engine until it matches the working tach.

I tried to clean up his instructions by only leaving what to do when using the engine instead of specialized electronic equipment and I am so lost, no clue how to calibrate the Tach

[enaberif]

Originally Posted by Gregski

God that site is horrible to read, thank you for the resource though, also I think all I may need to do is calibrate it, but he does not tell us how to do it

The potentiometer you install is how you adjust it. It has a small adjustment knob.
Link: http://www.howtoalmanac.com/kevin/pr...chfixtruck.htm
Image: http://www.howtoalmanac.com/kevin/im...trucktach3.jpg

Look at the blue box he soldered in and look at the bottom left you'll see the adjustment knob.

[hatzie]

I'd use my DC lab supply along with one of my HP2000CD, HP204C, or HP209A Audio Oscillators and set the oscillator using the frequency counter on my TEK 2236A Scope... but that's only because I have those toys.

The running engine's coil is a good enough frequency generator and the Inductive pickup tach can stand in for a frequency counter because it's a known calibrated measurement device.

Temporarily turn your idle screw up till the inductive tach reads 1500 RPM. Blip the throttle to make sure she settles back down at 1500 and adjust till it's stable after a quick blip.

Hook up the analog tach along with the inductive pickup tach, just like you did before, so you can read em both.

Turn the screw on the trimmer potentiometer you added in the repair outlined on the web page till the analog tach matches your inductive digital tach.

Run the throttle up to 2K on the inductive tach and check em both at 2K and 3K & then maybe 4K. If the analog tach is close you're done.

[Chaplain]

Oh my...

[77K10Silverado]

Gregski I may have missed it.....

BUT

what's the reason for the change to 78, just the oil gauge?

[hatzie]

Originally Posted by Chaplain

Oh my...

My test equipment is military surplus and Hamvention flea market gear so it was not that expensive. I probably have less than $500 in the whole bench. All but the TEK had to be repaired and cleaned up to make them serviceable.
I was able to cherry pick my TEK out of a stack of Surplus scopes and I got lucky.

[enaberif]

Originally Posted by 77K10Silverado

Gregski I may have missed it.....

BUT

what's the reason for the change to 78, just the oil gauge?

Oil, Tach, and removal of ammeter.

[Gregski]

Originally Posted by rusty76

Congrats on the score. Now find me a core support as well. Good luck. Mines not only rusty but bent as well......

Found one today, $30 bucks! Not perfect but still very solid under that surface rust in the bottom corner. Got it off of a '79

[Gregski]

just wanna beat an old horse to death and help some of you out who may have a '76 gauge cluster and want to see the pin out in color

[Gregski]

this is what the 1979 gauge cluster pin out looks like actual color wires

[Gregski]

Originally Posted by Chaplain

Oh my...

my thoughts exactly, LOL

[Gregski]

Originally Posted by 77K10Silverado

Gregski I may have missed it.....

BUT

what's the reason for the change to 78, just the oil gauge?

Hi Mike, someone already answered it, by my personal reason was just to find any ol' cluster with a Tachometer or even just the blueish/greenish plastic housing for the tachometer, the fact that I landed one with an electronic oil pressure gauge and a volt meter instead of an ammeter were just bonus