Tachometer question - electrical issue I caused
Thread Starter
Burning Brakes
Joined: Feb 2004
Posts: 1,212
Likes: 3
From: Bernardsville, NJ
Tachometer question - electrical issue I caused
Electrically-savvy tech heads - here is a conundrum for you!
So I'm trying to splice into a wire in the back of my tachometer yesterday to send an RPM signal to my TraqMate. I was testing a signal against the "+" spade terminal on the back of the tach unit, and by accident it brushed against the back of the tach housing while also touching the "+" spade, causing a spark.
The tach still functions as a tach, as do the turn signal indicators. Here is the odd part, and the question for those that have an aptitude in this area: The illumination lights in the Tach no longer come on with the light switch (all of the other gauges still work fine), AND the high beam indicator now shows blue when the low beams/fogs are on, and shuts off (no blue) when the high beams are ON. And it gets weirder! If I have the gauge pulled out of the dash and it rests with the rim of the tach against the rim of the speedometer, and I turn on the lights, the lights will function, and the high beam indicator works as it is supposed to. When I turn the lights off, the tach goes off, etc...but only when the black rim of the tach touches the speedometer black rim.
Any ideas? It is obviously getting some kind of a power source (ground?) from touching the other gauge, though when I put it back into the dash, it no longer works.
So I'm trying to splice into a wire in the back of my tachometer yesterday to send an RPM signal to my TraqMate. I was testing a signal against the "+" spade terminal on the back of the tach unit, and by accident it brushed against the back of the tach housing while also touching the "+" spade, causing a spark.
The tach still functions as a tach, as do the turn signal indicators. Here is the odd part, and the question for those that have an aptitude in this area: The illumination lights in the Tach no longer come on with the light switch (all of the other gauges still work fine), AND the high beam indicator now shows blue when the low beams/fogs are on, and shuts off (no blue) when the high beams are ON. And it gets weirder! If I have the gauge pulled out of the dash and it rests with the rim of the tach against the rim of the speedometer, and I turn on the lights, the lights will function, and the high beam indicator works as it is supposed to. When I turn the lights off, the tach goes off, etc...but only when the black rim of the tach touches the speedometer black rim.
Any ideas? It is obviously getting some kind of a power source (ground?) from touching the other gauge, though when I put it back into the dash, it no longer works.
5th Gear
Joined: Feb 2008
Posts: 5
Likes: 0
Tachometer question
You did not mention the year and model of your car. I am looking in the 1991 wiring diagram...
There are two paths to ground in this series with the 26 pin connector on the back of the tach. Both are brown wires. One is connected to pin 14, the other is connected to pin 15.
The weak point is the copper tracing on the circuit board. I suspect you brushed 12V against the tach housing and the voltage melted a wire tracing inside.
I think you are lucky, you just need to re-ground the metal case and you'll be back in business.
Good Luck, Mark
There are two paths to ground in this series with the 26 pin connector on the back of the tach. Both are brown wires. One is connected to pin 14, the other is connected to pin 15.
The weak point is the copper tracing on the circuit board. I suspect you brushed 12V against the tach housing and the voltage melted a wire tracing inside.
I think you are lucky, you just need to re-ground the metal case and you'll be back in business.
Good Luck, Mark
Thread Starter
Burning Brakes
Joined: Feb 2004
Posts: 1,212
Likes: 3
From: Bernardsville, NJ
Thanks, Mark!
My car is a 1983 911SC. Your comment, though, would seem to support what I'm finding.
Would you suggest that I simply run a ground wire to the back of the tach housing somewhere?
My car is a 1983 911SC. Your comment, though, would seem to support what I'm finding.
Would you suggest that I simply run a ground wire to the back of the tach housing somewhere?
