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Tachometer Failure


Darrin

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Hello All.

The tach on my 1990 LS400 has stopped working. All the lights work fine but the needle is way below 0 and only moves slightly as the engine revs. I assume I need to replace the whole cluster but wondered if anyone has had the same problem I'm having. Any input on what to do is greatly appreciated.

Thanks,

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So do you think there is a way the low short can be easily found and corrected? In this case another instrument cluster may not fix the problem. I'd buy one to try but the cheapest I'm seeing are a little over $100. I'm not sure what to do on this; I could live without the tach but still would like all to work properly on the car.

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It is possible the short is in the indicator..

The problem is you need schamitic to show you where wires go to. If you could disconnect and then check wire to ground.... Meaning you would check resistance and if it was infinite then you would know it is shorted to frame.. This is complex and if ends of wires are hard to get to it may be impossible to troubleshoot.

I think LEXUS has great wiring and would think its more probable for the short to be in indicator.

It is also possible the wires are partially disconnected.?

1. So check connection first..

2. Try to find source of wire? Maybe computer or the tach generator (Small generator that spins with tire revolutions) to disconnect and check resistance. You would have to disconnect both indicator and where wire ends on tach generator... On the air craft it was also possible for tach generator to short.

3. Buy indicator and replace.. OR R2 (remove and replace)\

Now none of this is a guarentee.. You see in the AF planes have up to 10 engines and we could switch gauges.. Good luck!!

GO BUSH!! THE only answer to terrorism is death to them!

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Ok. That makes sense. I'll try and dig into this in the next week. The wonderful thing about this old car is that I've owned it for almost 6 years now and this is the first type of failure of any kind. All I've ever done on the car is routine maintenence. Thanks a bunch for the guidance,

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I don't much care the the political interjection. This is one of the few places where people can still talk and agree and I attribute that to lack of politics here.

Try Iwon for that stuff.

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I have the same issue with my tach needle. It sits on the bottom of the display most of the time, but at high revs just moves a little towards the bottom of the scale.

Someone had once mentioned they found a ground problem with the tach....

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Sorry for the moment of pride for our president.. Since 2001 no bombs in America makes me happy!

Off scale low (short or open).. Usually short since insulation rubs off and then wire grounds to frame, screw or metal. Also indicator it self can have a short.

Cheers, Chris

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  • 3 months later...

Had a problem with tach, removed instrument pannel changed all small can caps on both ckt. boards also resoldered eyes . Eyes are little solder spots on the board where the electrical connections from one side of the board connect to the other side of the board . Sometimes the eyes break loose and lose connection. Also replaceing the caps will avoid problems with dash lights and radio and A/C console lights going out havent had a problem since. Knock on wood!

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