odd problem with factory tach

[Just Joel]

Alright, this is an odd one... installed a factory tach ( two white wires and a small loop) in my 510 when I was first putting the car together. Since getting it running, I found that every time I rev over 4k rpm, the tach takes off and inaccurately shows a higher rpm than actual. Another thing I noticed recently is that the blinker indicator lights in the dash go crazy while this is happening and flash very rapidly until I shift, then all goes back to normal. Any ideas why this is happening? The tach is hooked up correct to factory spec and I'm using a matchbox ei dizzy.

 

thanks

Joel

[Eagle_Adam]

:confused:

[Laecaon]

why would you do that?

[Just Joel]

lol, you bastards are quick... stupid phone posted early ;) fixed^^^

 

Joel

[Eagle_Adam]

Ah, well then..... im of no use :/ 

[Just Joel]

lol^^^^

 

I should also mention that the blinker indicator lights flush the same whenever I use the horn or use the high bean switch :/

[datzenmike]

Signal lights flickering has to be a wire touching something from vibration.

 

lol^^^^

I should also mention that the blinker indicator lights flush the same whenever I use the horn or use the high bean switch :/

 

These are both on the steering column. I would remove the wheel and take a good look at the combination turn signal/high beam switch.

[Just Joel]

I have removed and completely cleaned and reinstalled that switch twice now thinking it was a bad ground/connection... no dice. And the harness (both engine and dash) have been removed, cleaned and wrapped. all new and old connections were soldered and insulated so I don't think I have a crossed connection. To better explain the symptoms, both the left and right turn indicators are flashing like a machine gun in unison only while the engine revs over 4k rpm... this is also where I experience the arctic tach reading.

 

Joel

[Just Joel]

Grounding issue? Where should I look?

[Eagle_Adam]

have you looked at the hazard switch? 

[datzenmike]

Well if the dash signals are flashing then likely the turn signals front and rear are too.

 

Well was it wired this way:

(from the DQ post on tachs)

 

Black wire to ground, green wire to +12V, two white wires in series to the negative side of the coil. (This means remove the wire from the negative side of the coil and connect it to one of the white wires, and connect the other white wire to where the coil wire was.) If it still doesn't work, try reversing the two white wires.
 

If your tach has only three wires connect them like this: again Black to ground, Green to +12, and Black with green stripe to negative side of coil. (no series connection here).


 

[MikeRL411]

Outside chance as in improbable that you are getting cross coupling from unshielded wires in close proximity.  AKA RF interferance.  All to common in user "improved" wiring looms.

[Just Joel]

have you looked at the hazard switch? 

Yep, all looks fine and works great independently.

[Just Joel]

Well if the dash signals are flashing then likely the turn signals front and rear are too.

 

Well was it wired this way:

(from the DQ post on tachs)

 

Black wire to ground, green wire to +12V, two white wires in series to the negative side of the coil. (This means remove the wire from the negative side of the coil and connect it to one of the white wires, and connect the other white wire to where the coil wire was.) If it still doesn't work, try reversing the two white wires.

 

If your tach has only three wires connect them like this: again Black to ground, Green to +12, and Black with green stripe to negative side of coil. (no series connection here).

 

good point Mike... just checked and only the dash lights light up, no trails or front indicators. and wired per the first description from the dq article.

 

Joel

[Just Joel]

Is it possible that I'm getting feed back through a common ground in the dash?

 

Joel

[datzenmike]

Do the dash and the outside turn signals work normally? Well, normally below 4K?

 

Only way I can see both turn signals flickering is if there was a 12 volt source some how rubbing against the black ground wire for the turn signal lamps. Yes it would be a short to ground but it would also 'see' the ground through the six turn signal bulbs (two front and 4 rear) too. And because the signal lamps are only a few watts the outside lamps (20 watt? each) wouldn't have enough power to actually light up. As I said this would be a short to ground but it's very fast and intermittent.... perhaps not enough to burn wires or blow a fuse. Perhaps it's the power wire to the tach? This would also upset the tach and may make the readings go up.

 

Check the power wire used, from where ever you have it to the tack.

[Just Joel]

Could be, and to further dribble you additional information as I remember it, I changed the indicator builds to leds at the same time of the tach install. So what would explain the crazy tach readings over 4k rpm?

[bonvo]

replace guts of factory tach with aftermarket tach guts wire appropriately problem solved XD

 

honestly though im useless here as ive never played with a factory tach but im good at electrical bring it by and ill take a look man  

[datzenmike]

Could be, and to further dribble you additional information as I remember it, I changed the indicator builds to leds at the same time of the tach install. So what would explain the crazy tach readings over 4k rpm?

Same thing but even more so as LEDs make huge light with very little input power.

[Just Joel]

Same thing but even more so as LEDs make huge light with very little input power.

Yeah, I wonder if the light thing is just common and further exacerbated by the led's?

 

Joel

[Just Joel]

Update, the leds are the cause of the quick "blink" (thanks Mike) when using other accessories on our around the column. I switched them out for the original bulbs and all is fixed. I was actually already considering switching back because the led's are way too bright anyway.

 

Now, with that problem fixed, I still don't know why the tach goes crazy every time I rev over four k... any ideas?

 

thanks

Joel