Speedo maxed out when lights on ?

[stefzilla]

Hi all

Having some issues with my ph2 172.

As soon as my lights are on the speedo goes to max, until I turn them off again. This wouldn't bother me but the mileage is going up at some rate with it. I've had a quick look at the connections on all the lights and they all look clean and dry.

Has anyone ever had this before or know where else to check ?

Thanks

 

[DrR]

Never heard of that happening!

 

[Cookie]

Have you tried checking the fuses? Or calling in an exorcist?

 

[STEVE.M]

Hi all

Having some issues with my ph2 172.

As soon as my lights are on the speedo goes to max, until I turn them off again. This wouldn't bother me but the mileage is going up at some rate with it. I've had a quick look at the connections on all the lights and they all look clean and dry.

Has anyone ever had this before or know where else to check ?

Thanks

Never heard of it, but clarify what is going on, as we are already off to a bad start.

Ignition Off, but sidelights on, Speedo maxed out? YES?NO.
Ignition Off, but dipped lights manually on, Speedo maxed out? YES?NO

If not above, move on and repeat with Ignition on, but engine not running. Speedo maxed out? YES/NO?

 

[stefzilla]

Never heard of it, but clarify what is going on, as we are already off to a bad start.

Ignition Off, but sidelights on, Speedo maxed out? YES?NO.
Ignition Off, but dipped lights manually on, Speedo maxed out? YES?NO

If not above, move on and repeat with Ignition on, but engine not running. Speedo maxed out? YES/NO?

Sorry, Only does it if the engine is running and as soon as sidelights or any other lights are switched on the speedo hits top end.
Doesn't change if I'm stationary or moving.

 

[STEVE.M]

Sorry, Only does it if the engine is running and as soon as sidelights or any other lights are switched on the speedo hits top end.
Doesn't change if I'm stationary or moving.

Ok, that`s that out the way.

Is it a 2003 172 with a JC-130 gearbox, where the speedo is driven by an ABS ring, or a 2002 172 with a JC-129, where the speedo is driven by a manual drive at the back of the box?

Also if you do the clock function test, with the button on the RH column stalk depressed as you switch the ignition on, does the speedo go through it`s normal 3 step test, or go straight to the top?

 

[imprezaworks]

If atall possible can you check with another speedo unit as to wether yours is at fault.

 

[STEVE.M]

If atall possible can you check with another speedo unit as to wether yours is at fault.

The speedo obviously works, it`s just getting too much current from somewhere.
Cannot make any progress until my last questions get answered.

 

[imprezaworks]

Ok boss.

 

[STEVE.M]

Sorry, Only does it if the engine is running and as soon as sidelights or any other lights are switched on the speedo hits top end.
Doesn't change if I'm stationary or moving.

This is the speedo drive on the 129 box if you were not sure.

 

[stefzilla]

Ok, that`s that out the way.

Is it a 2003 172 with a JC-130 gearbox, where the speedo is driven by an ABS ring, or a 2002 172 with a JC-129, where the speedo is driven by a manual drive at the back of the box?

Also if you do the clock function test, with the button on the RH column stalk depressed as you switch the ignition on, does the speedo go through it`s normal 3 step test, or go straight to the top?

It is the JC-129. Just done the clock function that works all the way through.

I have another 172 so I can swap bits and pieces over if needed.

Another point the car came fitted with an omp wheel if that could cause any issues ?

 

[imprezaworks]

Interested to hear the outcome as obviously the car is thinking you are driving it

 

[STEVE.M]

It is the JC-129. Just done the clock function that works all the way through.

I have another 172 so I can swap bits and pieces over if needed.

Another point the car came fitted with an omp wheel if that could cause any issues ?

Well the fact that it`s a 129 is a relief, as I was worried it might be ABS related.

Just to be certain of this,does the speedo function normally during daylight hours, when the Auto lights will not activate?

Not sure why an OMP wheel would have any bearing, though has a PH1 switch with the horn been fitted?

Has the speedo done this since you have had this car?

Perhaps @bloke might have some ideas?

 

[stefzilla]

Well the fact that it`s a 129 is a relief, as I was worried it might be ABS related.

Just to be certain of this,does the speedo function normally during daylight hours, when the Auto lights will not activate?

Not sure why an OMP wheel would have any bearing, though has a PH1 switch with the horn been fitted?

Has the speedo done this since you have had this car?

Perhaps @bloke might have some ideas?

Yeah it works perfect when the lights are off.

Don't know about the horn the wheel was already fitted, my just swap back to the original just to rule that possibility out.

Started about two - three weeks ago but I have owned it since may.

 

[Gus]

You havent swapped any bulbs or anything recently have you?

 

[stefzilla]

You havent swapped any bulbs or anything recently have you?

Only today to check them all.

 

[STEVE.M]

Yeah it works perfect when the lights are off.

Don't know about the horn the wheel was already fitted, my just swap back to the original just to rule that possibility out.

Started about two - three weeks ago but I have owned it since may.

Perhaps someone who knows what they are talking about could take over from here!

I`d pull the plug from the speedo drive for elimination purposes, but I suspect it will be a problem with the circuit board in the clocks causing a bad earth or short, or possibly the switchgear.

If you have spares, substitution would seem the way to go.

Poor connections in the rear lights can cause problems, but I`ve not heard this one before.

Good luck!



I

 

[Gus]

I'm with Steve , sounds like its the clocks. turning the lights on illuminates the clocks which may affect the circuitry somehow.

Never heard of this problem before to be honest. I've heard of the Speedo needle dropping to zero when there is an issue with the earth strap that links the gearbox to the chassis.

@MicKPM have you ever seen this issue

 

[imprezaworks]

If atall possible can you check with another speedo unit as to wether yours is at fault.

So this then?

 

[STEVE.M]

I Give up.
" ONLY does it if the engine is running and as soon as sidelights or any other lights are switched on the speedo hits top end.
Doesn't change if I'm stationary or moving."

 

[bloke]

sounds a fun one, i'd go for unplug the drive first and see if it still does it. if it does check back lights, doubt it would be caused by them but the fuel pump is earthed through one side so it wouldn't surprise me though.

 

[STEVE.M]

sounds a fun one, i'd go for unplug the drive first and see if it still does it. if it does check back lights, doubt it would be caused by them but the fuel pump is earthed through one side so it wouldn't surprise me though.

The only thing I can think of that is different when the engine is running, as opposed to just having the ignition on, is that there is a signal to the tacho.

 

[bloke]

you could try taking the connector out of the plug for the speedo signal to rule the rest of the circuit out. or just unplug whatever one it's on.

 

[stefzilla]

Hi all finally got round to playing with the car turns out it was just a dodgy speed sensor.

Lights and everything on and it works fine now.
Thanks everyone for your help.

 

[mace¬]

Light speed?
Have you timed how long it takes to do the Kessel Run when the lights are on?