Hello all. I am new to this group and thanks in advance for any answers to my questions.
I own a 1978 4x4 F-150 Ranger standard cab longbed. My instrument cluster had dry rotted so badly on the back that the dash lights would no longer work. I purchased a used cluster and when I started to install it, lo and behold, Ford had used a different plug. My existing cluster has the idiot lights for oil and ammeter and a 14 pin connector. The new one (and only one I could find in decent condition) has the full gauge pack on it and an 18 pin connector. Does anyone have the wiring diagrams for both of these plugs so that I can change the plug itself and use the new cluster? I realize that the oil sending unit will have to be changed in order for the new one to work, but will anything have to be changed for the ammeter to work?

 

BTW, my truck has the 351M engine and auto transmission on the column, if it matters.

 

Welcome to the site

sorry but, You have to change the complete harness or find the correct cluster back.

Different systems.

You cannot rewire a Printed circuit.


I know where you can get a good Cluster back for idiot lights.

Btw, All users have 60 minutes to add or remove something from their own posts.
Just Click EDIT on the bottom right of your post next to the QUOTE button ......instead of clicking post reply again

 

Daves: A couple of questions for you....what year truck did you get the new instrument pack from - same as your truck?? Have you made a list of the colour codes of the 14 wires from your old pack and compared the colours to the new 18 pack? If you are a luck man, 14 out of the 18 will be the same. (In the back of the Haynes manual, there are multipages of wiring diagrams for your truck.)

Hooking up the oil pressure sender wires should be straight forward but older design ammeters can be tricky and dangerous. You might be able to find out how the ammeter citcuitry is set out on the new instrument pack by looking at the gauge of the ammeter wire ...if it is a very heavy gauge- 8 gauge then ALL the alternator current is routed to the gauge and then back to the regulator (in series)....if the wire is a thin one 14-18 gauge, then the ammeter works in parallel and is the modern type. My experience is with much older vehicles than your truck. Cheers.

 

Mr. Fixit, The new cluster also came from a '78 F150 Ranger. All of my existing wires look to be 14 to 16ga wires. I do not have the plug for the 18pack in hand yet , but should have it soon.
To 1 in a million I am not looking to rewire the printed circuit sheet. I am looking to replace the existing instrument cluster with another and change the plug that connects to the back of the cluster from the vehicle. Most of the wires have the same purpose, but may connect in a different socket.

Thank you both

 

I would just suggest 2 get the right cluster and if u want actual gauges go with a set of aftermarket, as for the ammeter, go with voltmeter instead, ammeters can be dangerous to wire and if done incorrectly can cause a fire...........just my opinion, and I had the same problem not long agao with the different clusters, and replacing the wiring harness is not a hassle I'd wanna take

 

I know what you are trying to do.

You want to pin the 18-pin connector with wires from the 14-pin harness.

I have answered at least 30 of these same threads

The 18 pin cluster uses a 18 pin printed circuit

The 14 pin uses 14 pin printed circuit .

It is that much Different that it is not interchangeable with the 18 pin system

You can't interchange them.

The sending units are different ..the ammeter wiring is different

You use one or the other.
By the Harness you have.
You want gauges ? get the 18pin gauge wiring harness.

You never said what year gauge cluster you got.

 

Oy! Disregard my comments Daves....clearly these are two different electrical systems. Sounds like you're going to have to change over the other wiring harness and different sensors if I understand Mil1ion's post.
It might be easier just to add aftermarket oil, voltmeter &/or ammeter and clean up your existing wiring...

 

I have to agree with Mil1ion.


There are at least 15 different circut differences between the Main harness wired for gauges, (18 Pin) to the main harness wired for idiot lights. (14 pin)

It's not just rewiring it at the instrument cluster.

The whole charging system would have to be rewired from the altenator to the voltage regulator, to the instrument cluster.

Then you would have to rewire some of the power distribution, off of the starter solenoid.

Then you would have to find resistor wire, fuse links and shunts of the right type.

It is not a simple task at all.

It is much easier to replace the main harness, for one with gauges (18 pin cluster connector). And a lot safer. And the only way to convert a truck from idiot lights to gauges that I recommend.

Better yet, it's easier still to just replace the cluster plastic with the correct type.

Hope ths helps.

 

OK now you have roused my curiosity. Other than the Ammeter wiring and the Oil Pressure gauge wiring, What is the major difference(Other than wire locations at the plugs) between the two clusters?

 

Slow down, Guys! It can be done, but you are in for a lot of heartache. I did mine by using my existing 74 full guage cluster with a 77 harness out of my donor truck. The oil press works fine, but the ammeter has always read high since my GM alt. swap.

What I did was to take the 74 plug, cut off all the wires at about 10" and install spade connectors. On the 77 harness, I installed the spade receivers, and then I spent about 2 weeks tracing wires to figure out what each pin # on the circuit board did. You are fortunate that you are using the same year stuff. You can take the pins out of the 14 plug and reinsert them in the 18. They had different retainer clips for different years (I think) I can share my info with you if you want, but I am pretty sure that all my stuff is different since I didn't use anything 78.

 

Actual Ford Part Numbers For F Series Printed Circuits 1970-1979

1970 F100-F350 W/gauges: D0TZ-10K843-A

1970 F100-F350 W/lights: D0TZ-10K843-B

1971-72 F100-F350 W/gauges: D1TZ-10K843-A

1971-72 F100-F350 W/lights: D1TZ-10K843-B

1973-74 F100-F350 W/gauges: D3TZ-10K843-A

1973-1975 F100-F350 W/lights: D3TZ-10K843-B

1975 F100-F350 Before Serial # W40,001 W/gauges: D5TZ-10K843-A

1975 F100-F350 After Serial # W40,001 W/gauges: D5TZ-10K843-C

1976-1979 F100-F350 W/gauges: D6TZ-10K843-B

1976-1978 F100-F350 W/lights: D6TZ-10K843-C

1979 F100-F350 W/lights: D9TZ-10K843-A

 

Unless he really wants gauges ,I think I woud be much easier for me to send him a proper cluster back

When one fools with wiring, one can get burnt.....sometimes the truck goes up in smoke as well.

 

There are a number of years of Van clusters that also interchange with the F series trucks, clear up to the late 80's. The years are listed in the FAQ thread, tips and tricks.

 

You want to know the major circut differences. I'll get my trusty Ford wiring diagrams out and check for the 1978.

Well the first circut differences is coming right off the starter solenoid.

A: Truck with Gauges:

1: Circut #38 BK/R wire from starter solenoid is a fuse link untill it reaches splice #201, where circut #655 R/O wire splits off and goes to the ammeter.

2: Then from Splice-201 circut # 152 Yellow wire goes to the altenator regulator.

3: Then further down, circut 38 BK/R, (no longer a fuse link after S-201), between S-201 and S-202 there is a shunt, then at S-202, Circut 654 Y/BK goes to other side of the ammeter.

4: Circut #38 BK/R continues to Altenator Regulator.

5: Circut # 37 BK/Y wire goes to the S-208 where it splits into circut #25 Bk/O that goes to the headlamp switch,

6: Then circut-37 BK/Y goes from S-208, where it splits off and half goes into the fuse block, fuse #'s F-7 and F-8, then the other half goes to S-402, where the Circut # is changed to 21 Yellow where it enters the ignition switch.

====================

On Trucks with Idiot Lights.

1: Circut # 37 Bk comes right off the starter solenoid, and is a fuse link until it reaches S-207, where it continues as regular wire.

2: Then circut-37 BK/Y goes from S-207, were it goes to S-208 where it splits off and half goes into the fuse block, fuse #'s F-7 and F-8, then the other half goes to S-402, where the Circut # is changed to 21 Yellow where it enters the ignition switch.


3: Circut # 38 BK/R also comes off the starter solenoid where it is a fuse link until it hits splice S-203.

4: Then from Splice-203 circut # 152 Yellow wire goes to the altenator regulator.

5: Circut #38 BK/R From S-203 continues to Altenator Regulator.

That was just the differences in Power distribution, for ammeter hookup.

================================

Now the differences at the Voltage Regulator and Choke, and instrument cluster.

For Truck With Gauges.

1: Circut-4 W/BK, goes from the altenator S terminal directly to the Electric choke via a fuse link.

2: Circut-904 GR/R hooks to the S terminal of the regulator.

3: Circut-904 GR/R then goes to S-401 where it splits off to Circut-640 R-Y and circut-16 R-GR.

4: Circut-640 from S-401 goes to Brake Warning light and Fuse panel Fuses # F-5 and F-6.

5: Circut-16 goes to Ignition switch.

6: The I Terminal at the regulator is left blank.

7: Circut-297 BK-GR goes from ignition switch to S-303 where the circut is changed to #30 BK-GR where it goes through a 9 OHM resistor, to the Instrument cluster voltage regulator.

8: Circut-30 BK-GR powers the fuel, temp and oil pressure gauges.

9: Circut-31 W-R, goes from the oil pressure gauge to the sending unit.

For Trucks with idiot Lights.

1: Two wires, one Circut-4 W/BK goes from altenator S terminal goes to regulator S terminal. The other goes to the electric choke.

2: Circut-904 GR/R hooks to the I terminal of the regulator.

3: Circut-904 GR/R then goes directly to the instrument cluster connector and the altenator idiot light.

4: Circut-98 BK goes from instrument cluster connector and Alt-idiot light from circut-904, and goes through a 15 ohm resistor.

5: Circut-98 BK continues to S-305 where it hooks into Circut-297 BK-GR

6: Circut-297 BK-GR goes from ignition switch to S-305, where Circut-98 hooks into, then circut-297 goes to S-303 where the circut splits, one the circut is changed to #30 BK-GR where it goes through a 9 OHM resistor, to the Instrument cluster voltage regulator. The other remains Circut-297 BK-GR and goes to the other end of the alt-idiot light.

7: Circut-16 R-GR comes off the ignition switch, and hooks to S-401 where it hooks into circut-640 R-Y, where one half goes to fues box Fuse #F-5 and F-6, and the other goes to the brake warrning light and oil pressure lamp.

8: Circut-31 W-R goes from the oil pressure light to the Oil pressure switch.

=================

As you can see, the main harness for gauges and idiot lights are wired totally different from each other.


Easier to swap main harnesses. believe me. It's safer too, than to rewire all of the above.