Board logo

Speedo and Tacho problem
Schrodinger - 1/4/26 at 04:44 PM

My speedo and tachograph drop to zero when the indicator lights come on. All of my other instruments appear OK but they all move slowly and are probably dumped so they do not show any movement as my indicators flash. All instruments are ETB, speedo, tachograph, fuel, oil pressure and water temp.
I have just replaced the signal and earth wires on the two affected instruments but I still have the same problem. Can anybody suggest the next move?

Slimy38 - 1/4/26 at 05:14 PM

Have you checked the earth on the indicators? If the indicators are managing to put 12 volts where it shouldn't be then other electrical thingies could go wonky.

gremlin1234 - 2/4/26 at 06:41 AM

certainly sounds like an earthing issue. (suspecting earthing fault in side light/ indicator bulb/housing )

can you please try:

does it fail on both left or right

does if fail with hazzards (rather than individual indicators)

is the battery fully charged?

can you try it with the side lights on

also are you using led or conventional bulbs?

edit to add
is the battery fully charged

[Edited on 2/4/26 by gremlin1234]

gremlin1234 - 2/4/26 at 09:38 AM

thinking about this more, I currently suspect a fault in the common earth behind the dashboard.
as well as the tests in my previous post I suggest disconnecting the indicator 'tell tail' on the dash, to see if the fault continues.

Schrodinger - 2/4/26 at 10:56 AM

quote:
Originally posted by gremlin1234
certainly sounds like an earthing issue. (suspecting earthing fault in side light/ indicator bulb/housing )

can you please try:

does it fail on both left or right

does if fail with hazzards (rather than individual indicators)

is the battery fully charged?

can you try it with the side lights on

also are you using led or conventional bulbs?

edit to add
is the battery fully charged

[Edited on 2/4/26 by gremlin1234]



Thanks for your thoughts

the problem occurs when indicating right, left and when the hazard lights are used. Also when the battery is fully charged and side lights on (they dim slightly along with any warning lights that are illuminated. I have checked the flasher relay earth and the rear indicator bulb earths and they seem ok. I'm just having lunch and will check the earth on th front indicators this afternoon along with disconnecting the tell tales on the dash, to see if that has any effect.
The only led's are on the number plate.

Thanks for everybodys help so far.

[Edited on 2-4-26 by Schrodinger]

gremlin1234 - 2/4/26 at 11:58 AM

quote:
Originally posted by Schrodinger

Thanks for your thoughts

the problem occurs when indicating right, left and when the hazard lights are used. Also when the battery is fully charged and side lights on (they dim slightly along with any warning lights that are illuminated. I have checked the flasher relay earth and the rear indicator bulb earths and they seem ok. I'm just having lunch and will check the earth on th front indicators this afternoon along with disconnecting the tell tales on the dash, to see if that has any effect.
The only led's are on the number plate.

Thanks for everybodys help so far.

[Edited on 2-4-26 by Schrodinger]


since it does not occur on left indicator, I don''t think you need to test the panel tell tail. (unless you have separate left/right panel indicators...)

almost certainly an earth fault on either the front or rear indicator bulb or socket.
further testing would include testing while brake lights are on,

but currently I suspect front right indicator earthing.
& try a different bulb (I have seen bulbs with internal faults!)

[Edited on 2/4/26 by gremlin1234]

jacko - 2/4/26 at 12:48 PM

Have you got a earth from engine to chassis if you are they in good condition and clean ends

Has the battery got good clean terminals

The problem sounds very much like bad earth time to start cleaning
G

Schrodinger - 2/4/26 at 04:02 PM

Well I checked the front indicator earths anlong with the relay earth and all seemes ok.

I think the next step will be to clean all the earth connections as Jacko suggests. After that I think its rewire the complete dash one thing at a time.

But that will be for another day for now.
and thaks for the suggestions.

[Edited on 2-4-26 by Schrodinger]

[Edited on 2-4-26 by Schrodinger]

[Edited on 2-4-26 by Schrodinger]

gremlin1234 - 2/4/26 at 04:10 PM

quote:
Originally posted by Schrodinger
Well I checked the front indicator earths anlong with the relay earth and all seemes ok.

I think the next step will be to clean all the earth connections as Jacko suggests. After that I think its rewire the complete dash one thing at a time.

But that will be for another day for now.
and thaks for the suggestions.
as I said, try changing the bulb. I have seen them fail internally