Tachometer Stopped Working

[Shadowman]

Shadowman - every time I get that "electrical handshake", it reminds me that I am highly alergic to volts, watts and amphere's.

Me too

Shadowman

 

[KMCBOSS]

I had a chance to look at the FGT instrument cluster wiring diagram and have a few observations to share.
1. all gauges have 4 terminals

2. all gauges share a common +12 volt reference line (a light green with red stripe wire number 235)

3. all gauges share a common LED illumination voltage line (a red with black stripe wire number 1246)

4. all gauges share a common signal return line (a black wire number 57)

5. the only unique input to each gauge is a control voltage from a funtional sensor (tach, speedo etc through the gauge control module)

6. Before replacing a suspect gauge I would recommend checking the continuity of the gauge wiring back to the gauge control module for the function control voltage and signal ground. The +12 and gauge illumination voltage can be checked to another gauge. Disconnect the gauge from the harness before checking continuity to avoid a false reading through a feed back loop.

7. If one gauge is inoperative -
the gauge may be defective (replace gauge)
or
the control function voltage is missing from the gauge control module (replace control module)
or
there is a bad connection on the +12 reference voltage line (repair connector/replace wire)
or
there is a bad signal ground connection (repair connector/replace wire)
NOTE the signal ground is also controlled by the gauge control module - so a problem in the gauge control module would affect all gauges.


A simple digital multimeter and the FGT wiring diagram may help you localize the problem


Ed

 

[ViperJoe]

30/4038 failures is very small

That would be correct if 4038 weighed in on the issue as opposed to the fraction that did. If the voting population were 300 the failure rate would be 10% as opposed to the <1% derived from the initial assumption. Accordingly, a failure rate in between these two numbers seems to be a reasonable conclusion.

 

[BlackICE]

Can the gauges be testing using the follow method?

Connect to ground of power supply - common signal return line (a black wire number 57)

Connect to regulated +12 volt supply - reference line (a light green with red stripe wire number 235)

Connect to adjustable voltage source and sweep from 0 to 5v slowly starting from 0 going to 5v, or 12v (stop at whatever voltage is needed to reach full scale or 5v or 12v, whichever comes 1st, only going to 5v is safer without specs) - the only unique input to each gauge is a control voltage from a functional sensor (tach, speedo etc through the gauge control module)

Connect to 5v should light up - common LED illumination voltage line (a red with black stripe wire number 1246)

 

[BillyGT]

I did go to a Ford Dealer and watched the technician use a device that could toggle any guage in a multitude of measurements. At this point the technician is saying the Tach and oil pressure gauge needs to be replaced:ack

 

[Shadowman]

I did go to a Ford Dealer and watched the technician use a device that could toggle any guage in a multitude of measurements. At this point the technician is saying the Tach and oil pressure gauge needs to be replaced:ack

The systems used is the IDS; I have one in my facility and you can bring the control module and the gauges on line.

Shadowman

 

[KMCBOSS]

Can the gauges be testing using the follow method?

Connect to ground of power supply - common signal return line (a black wire number 57)

Connect to regulated +12 volt supply - reference line (a light green with red stripe wire number 235)

Connect to adjustable voltage source and sweep from 0 to 5v slowly starting from 0 going to 5v, or 12v (stop at whatever voltage is needed to reach full scale or 5v or 12v, whichever comes 1st, only going to 5v is safer without specs) - the only unique input to each gauge is a control voltage from a functional sensor (tach, speedo etc through the gauge control module)

Connect to 5v should light up - common LED illumination voltage line (a red with black stripe wire number 1246)

The functional sensor control voltage may be way less than 5 volts for a full scale reading so care must be exercised here. We really need the output specs for each gauge functional sensor control voltage as they might not be the same. Also all power supplys used for testing (+12, functional control voltage and LED control) will need the negative connected to the signal return.

 

[KMCBOSS]

I'm working on 500 posts here so bear with me!
It is possible that this common knowledge, but just incase it isn't - when connecting your battery tender to the GT, make sure the tender is unplugged from the wall outlet before connecting to the GT's battery. After the battery tender is connected to the cars battery then plug it into the wall outlet. This will help keep transient voltage spikes from being generated in the electrical system.

 

[Kayvan]

Now we are getting to brass tacks....volts, lines, grounds

Someone is going to get snowed in take apart their dash and test every current...

 

[KMCBOSS]

One other item for folks that have their dash torn apart. The +12 volt reference line (a light green with red stripe wire number 235), LED illumination voltage line (a red with black stripe wire number 1246), and the signal return line (a black wire number 57), appear to be laid out in the harness with one wire per gauge that is crimped at some point. These crimps can fail if not done correctly, causing a disconnect in the electrical system. Thats why it is import to thoroughly check the continuity of the gauge circuitry before spending a grand on a new gauge.

Ed

 

[Kayvan]

Isnt there software that you can load up a schematic wiring circuit, test multiple nodes, and run multiple variables and graph probabilities of configurations and their related load ranges/failures.

Like this stuff

http://www.tech-systems-labs.com/freesoftware.htm

 

[fjpikul]

Are you impying Ford consulted Lucas on the wiring?

 

[Kayvan]

Are you impying Ford consulted Lucas on the wiring?

I was thinking more like Count Dracula

 

[BillyGT]

Tach will be coming back to me tomorrow

:banana I will let you all know how it works out :biggrin

 

[BillyGT]

Still got issues

:frown I got the tach back and tonight I just plugged it in and nothing but the light came on. All the other gauges except for the oil pressure and the tach were working :confused

New battery, ground checked and cleaned WTF!!!

Is there a fuse or something that I am missing?

 

[Empty Pockets]

:frown I got the tach back and tonight I just plugged it in and nothing but the light came on. All the other gauges except for the oil pressure and the tach were working :confused

New battery, ground checked and cleaned WTF!!!

Is there a fuse or something that I am missing?

"GULP":willy:willy:willy

...uuuuuuuuh...what about that $5K black box that "controls"(?) all the gauges? Was that ever checked out?

 

[BillyGT]

$5K Box

I had the dealer check gauges but can you check to black box stand alone?

 

[racelance]

Bummer! Sorry to hear this... Thanks for keeping us posted.

 

[Empty Pockets]

I had the dealer check gauges but can you check to black box stand alone?

I'm sure there has to be a way to do that. But, as "Spirit" would say, "that's way above my pay grade" as far as specifically HOW to do it. That'd be Shadowman's, or Kendall's, or the GT Guy's, or ?'s territory.

 

[KMCBOSS]

I believe the Shadowman (Bill) has a device to test the tach and other gauges. Recommend sending him a PM. If the gauge checks out then there are only two other components in that system - the control module and the wire harness. A connector pin may be broken or a bad crimp causing a loss of signal (12V and tach signal inputs) at the tach. A simple continuity test should be able to check the harness connections. Ed