Need help on a friend's boat - Tach/Speedo Not Working

[cloudd21]

Got a 99 crownline boat the tach gauge does work but the hours show up or miles and speedometer doesn't work either the back light works it has 5.7 gsi engine in it

 

[tpenfield]

OK, we’ll be right over.

 

[cloudd21]

I need advise what to look for to diagnose it then to fix it

 

[GA_Boater]

In summary;

• Tach works
• Instrument backlighting works
• Hourmeter in tach works
• Speedo doesn't work

Correct?

 

[cloudd21]

Tach doesn't work

 

[GA_Boater]

tach gauge does work but the hours show up

Tach doesn't work

Wonder why we're confused?

Does the speedo work? Any other non-working instruments?

 

[Scott Danforth]

tach has 3 wires to the gauge and 2 to the light

the light is a blue wire (light power) and black wire (ground)

the tach is a grey wire for signal (runs to negative terminal on coil), purple wire for power (ignition power from key switch) and black wire (ground)

so if the tach is not working (still confused on this), then either there is no power on the purple wire, or a bad connection on the black wire or there is no signal on the grey wire or the tach is dead

 

[cloudd21]

The speedometer doesn't work either so do I need to test which wires how can I test them

 

[kawakx125]

good lord i'm confused. best i can figure is that neither gauge works, which would lead me to believe there is a power issue somewhere else possibly

 

[cloudd21]

I have power to purple wire when key is on is there a way I can test the grey wire for the tach

 

[Maclin]

The speedometer probably runs off a pitot tube that runs up from a fitting on the transom.

 

[cloudd21]

I cleared the line with water and made sure the tube on the boat was clear of debris and dirt so know how can I test the speedometer gauge

 

[Scott Danforth]

The speedometer doesn't work either so do I need to test which wires how can I test them

use a multi-meter, set it to frequency, read the frequency at the coil with the motor running, then read it at the gauge....should read the same

I cleared the line with water and made sure the tube on the boat was clear of debris and dirt so know how can I test the speedometer gauge

blow in the tube, gauge should move