Leeroy_25

Guy's has anyone got a wiring diagram for the F100 CPU#2 on the FD3 please? I want to try and figure out which wire from the Tach goes to the CPU to sound the buzzer so I can cut it! My buzzer is going of at 4600rpm which is hell on the motorway so I want to shut it up as I don't think the FD has a way to adjust it like some of the older models. I want to keep the buzzer for low water and stuff though hence I don't want to just take the buzzer right out.

Thanks for any help.

DaleClark

iTrader: (55)

It's in the shop manual, just download and look in the wiring diagrams.

Dale

Leeroy_25

Okay.. So I can see a diagram of the cluster which shows 2 wires going into CPU#2. neither of these are labelled with a number or colour. If I find the CPU diagram none of the wires are labelled for Tach? a few labelled for instrument cluster but that is all? More help needed here please unless I am missing something obvious?

DaleClark

iTrader: (55)

Looking at the wiring diagram I'm 90% sure it's the brown (color code BR) wire from pin 3B on the cluster to 1L on the CPU.

That's the only wire that goes from the part of the cluster that has anything to do with the tach to the CPU.

The body electrical troubleshooting guide has more info on troubleshooting individual circuits like the warning buzzer, but the site I was on didn't have that. I have the real paper shop manual at home .

Back that wire out of the connector or snip the wire where you can re-attach it and give it a try.

Dale

Leeroy_25

Thanks for looking into that Dale. I see the wire o. The diagram. So cpu on the instrument cluster diagram refers to the instrument cluster CPU. So water level sensor and everything else feed I to that. So if I pull this brown wire will that not prevent the water level sensor sounding as well? I really don't want that! I cam easily test it by pulling the plug of the level sensor which should sound he buzzer. But that's what it looks like if it's the only feed into the F100 box?

DaleClark

iTrader: (55)

That may be the case. The root of the problem is the tach putting out what it shouldn't put out for some reason, like the needle is calibrated way off or something. Don't know if it would be worth trying another tach assembly.

Dale

Gen2n3

iTrader: (1)

Leeroy, I too looked at the schematic from the body electrical troubleshooting manual. I recommend not pulling the wire because it is multi-functional. If the Brown wire is pulled, it will affect the logic for the coolant level sensor as well.

Refer to Flowcharts 23 and 24 on pg C2-34 through C2-36 and wire schematics C-1a and J-4.

Flowchart 23 Symptom: Coolant level warning alarm does not sound when coolant fluid low level (coolant level warning light illuminates)
Flowchart 24 Symptom: Over-revolution warning alarm does not sound when tachometer indicates red zone

The first 3 troubleshooting steps are identical for both symptoms.

I agree with Dale - the tachometer is out of adjustment or is bad. Try to swap your tach with a known good unit. It may also be worth inspecting the speedometer circuit board since the tach receives inputs from it.

I suspect that Flowchart 24, Step 4 may yield an answer! If the reference voltage (3 - 6V) is off then perhaps the variable resistor on the tach could affect the buzzer? Just be cautions because that variable resistor on the tach would significantly affect the needle direction. BTW, a 3V swing for the reference voltage is HUGE!!!

Dale, did I read it correctly: you don't have an electronic copy of the Body Electrical manual? I could send you and/or Leeroy the file, as needed. It only covers the 94, but I suspect the differences are minor.

Cheers,
George

Leeroy_25

Hi George,
Thanks for the info.
So.. Back track a bit. I got the car as a non-runner and tach needle was doing all kinds of crazy things when you put the ignition on. I took out the cluster and followed the repair guide form on here. replacing the capacitors and resoldering the joints. Put it back and it worked fine other than rpm was reading too high. So I corrected that by adjust the blue dashpot think on the tach circuit and then now I get to drive the car and open it up a bit I found this issue. So... Assuming I marked and reassemble the tach needle correctly which I am 99.9% I did then I have two possibilities. Something else like the resistor you mention (Unless that is the blue thing I have adjusted) is bad and needs changing. or maybe when the need was going mad it spun the shaft and hence the needle although put on where it came off is actually in the wrong place? I don't think the latter is the case as when it did on occasion work it seemed to read about the right rpm? Maybe one of the components I put back is not sized as it should be and causing the issue?
Could I take the tach needle off again spin it around say 3000rpm (if it will still zero okay) and then re-calibrate the dashpot? In fact I would guess I have to spin it only 1500 as the when re-calibrate the dash pot another 1500 that is the right amount. From memory that is probably roughly the amount it was reading out when I first reinstalled it after repair?
Will try and find a spare tach to test and make sure it is the cluster that is the issue but being the history of it I would be surprised if it wasn't!
Thoughts please?

P.S.
Yes please to a copy of the manual please! Thank you.

Cheers
Lee

Gen2n3

iTrader: (1)

Lee,

First, the easy part - PM me your email addy so I may send the file. I may do a dropbox link because the file is just over 20MB and mail servers may not like it.

Onto the tach. Yes, I bet dimes to donuts that the tach is the culprit. When you say the car was a non-runner, what didn't work? Did anyone before you play with the electrics?

If you adjusted the blue pot then yes, that is the variable resistor I mentioned earlier. It is labeled VR1 for variable resistor, coincidentally. It is important to remember that there is a variable resistor on each board - 1 for the tach as VR1 and the other labeled VR on the speedometer circuit board.

Did you make repairs to the speedometer circuit board (the one with the odometer)? Which pot did you adjust - VR1 on the tach or VR on the speedo board? Did you make any repairs to the tach's (small) circuit board? Lastly, did you remove the face of the tach from its circuit board?

In case you made repairs to the tach board, there is a thread that covers removal and installation of the tach needle and face. I don't believe the the tach motor has a limited range of motion - it should only rotate faster or slower. Then again, I have not played with my tach other than documenting part numbers for a thread.

Have you verified that your wiring is ok? It may be a good idea to double check the speedometer circuit board for any other anomalies. When did you make repairs to that board? Pay attention to the color and shape of the solder joints to your replacement components. It should look like a shiny mountain peak.

Cheers,
George

Leeroy_25

Okay.. so the car had a blown engine. Which I swapped out for a 20B. Speedometer works fine. So I have only pulled out the tach and followed the procedure on here somewhere of repairing that with new capacitors and resoldering all joints. So face and needled were marked and removed. board taken off. repaired and then all put back and correctly aligned to the best of my knowledge. it worked fine other than I had to dial the needle in by adjusting the tach resistor. have touch nothing else. My theory is if I spin the needle by 50% of the error and re adjust the pot most like/hopefully back to where it started then I get the right readout and right signal output to the buzzer? but not being sure how the circuit and output works I don't know if that will have the desired effect?

Gen2n3

iTrader: (1)

Lee,

What components on the tach did you replace? And did you replace them with the exact same values? For example, C1 on the tach is a 1uF, 50V capacitor. A replacement capacitor must reflect the same values otherwise the system would need to be adjusted more than usual.

Cheers,
George