Speedometer and tachometer both "gone" simultaneously. (1 Viewer)

[fjgdk]

Both my speedometer and tachometer both stopped working at the same time on mystic 1983 FJ60. By stopped working I mean "both don't move from zero".

If the tach is based on a signal from the voltage regulator, and the speedo is based on a signal from the speedo gear in the tranny housing, what could possibly cause them to go up at the same time ?

The odometer isn't working either.

The fuel, battery, water temp and oil pressure meters all appear to be working.

I will go through typical "scientific method" troubleshooting when I get over the cold I have and it is warmer outside. I was just hoping for some initial thoughts.

 

[3_puppies]

stock? the speedometer and odometer are run off a cable assembly from the rear of the transfer case.
they are not linked in any form or fashion.
IIRCC the tach gets it's signal from the alternator

 

[FJ60Seth]

Does the car run?

Just kidding. I have no idea.

 

[g-man]

Not related except for the lighting for both. Tach gets a signal from the coil. and Power from the ignition then thru the engine fuse.

The speedo is purely mechanical gears and the cable coming into it from the transfer case output shaft has a square end that mechanically turns the gears...no electrical. I'd check the connections at the speedo first, then at the t'case. Spray some lube in it while you're in there.

Take a 12v test light and probe the black/yellow wire coming into the tach while the ign is on to check for power. Looks like a black wire is the signal wire coming from coil. Maybe it's rusty contact at the coil?

 

[g-man]

tach pictured here lower right, b-y is black w/yellow power wire, you can see this wire powers lots of other gauges and switches so most likely the issue is the signal wire at the coil.

 

[Seth S]

Maybe the speedo drive cable fell off the back of the speedo and knocked the tach connector off the back of the tach at the same time.

 

[fjgdk]

stock? the speedometer and odometer are run off a cable assembly from the rear of the transfer case.
they are not linked in any form or fashion.
IIRCC the tach gets it's signal from the alternator

Yeah I had actually pulled the whole dash apart about 8 years ago when I first got the truck to clean up mouse turds within the ac/heater air pathways. I remember the speedo cable was a separate deal from the other gauges so I couldn't understand how both the speedo and tach both went out at the same time.

View attachment 1868381

tach pictured here lower right, b-y is black w/yellow power wire, you can see this wire powers lots of other gauges and switches so most likely the issue is the signal wire at the coil.

Thanks for the schematic, I will test this when I get back out there on the truck. I have the body/chassis fsm and will look for this schematic in there.

Maybe the speedo drive cable fell off the back of the speedo and knocked the tach connector off the back of the tach at the same time.

That is an excellent hypothesis. I hope it is just what you said.

 

[3_puppies]

if the speedo cable is hooked up to the back of the cluster, you can take the end off the transfer case and put it in the chuck of a drill, going in reverse and the speedometer should move and the odometer should turn.