RedRide
07-19-2009, 02:30 PM
As many who have installed an after market tach in a HB, I found that the tach's night time illumintion was too bright.
Tapping into the dimmer circuit can be too contrived and doesn't seem to work with many tachs from what I have been reading.
Personally, I didn't want to constantly adjust the brightnees... just set it and forget it as I did/do with my EL gauges on my Celica.
So, I went to Radio Shack and got a 1K ohm potentiometer (# 271-342) and wired it in line with the illumination current source. This is only $2.69. You want the 1K ohm unit, not the the 10k ohm unit that looks the same and has an almost identical mumber!
After much research on the net, I discovered that some others were doing the same with various tachs with great results.
Most all modern tachs draw extremely low current for the illumination and this works well.
Personally, I have a "SpeedHut Revolution" tach.
Just solder one wire to the post nearest the adjustment screw and and the output to the middle post. The other post is not needed and can be clipped off
Cover the post/solder joints with heat shrink tubing for insulation and for added strength.
The adjustment screw can now be turned to fine tune the voltage( resistance) to the illumimation to adjust the brightness.
Potentiometers and rheostats both do essentially the same thing... vary restistance. I could not find a suitable rheostat for this purpose.
The whole assembly can be neatly tucked away with the rest of the wires from the tach install on the convienet shelf created by the bottom of the dash in that area.
BTW, I like to install after market gauges like this with snap together M/F crimp on connectors. This makes installing something like this simply plug and play.
I just installed a male connector to one lead wire from the potentiometer and a female connector on the other lead to connect it to my existing install :smile:
Below is a pic of the potentiometer which is actually a bit larger than actual size
Tapping into the dimmer circuit can be too contrived and doesn't seem to work with many tachs from what I have been reading.
Personally, I didn't want to constantly adjust the brightnees... just set it and forget it as I did/do with my EL gauges on my Celica.
So, I went to Radio Shack and got a 1K ohm potentiometer (# 271-342) and wired it in line with the illumination current source. This is only $2.69. You want the 1K ohm unit, not the the 10k ohm unit that looks the same and has an almost identical mumber!
After much research on the net, I discovered that some others were doing the same with various tachs with great results.
Most all modern tachs draw extremely low current for the illumination and this works well.
Personally, I have a "SpeedHut Revolution" tach.
Just solder one wire to the post nearest the adjustment screw and and the output to the middle post. The other post is not needed and can be clipped off
Cover the post/solder joints with heat shrink tubing for insulation and for added strength.
The adjustment screw can now be turned to fine tune the voltage( resistance) to the illumimation to adjust the brightness.
Potentiometers and rheostats both do essentially the same thing... vary restistance. I could not find a suitable rheostat for this purpose.
The whole assembly can be neatly tucked away with the rest of the wires from the tach install on the convienet shelf created by the bottom of the dash in that area.
BTW, I like to install after market gauges like this with snap together M/F crimp on connectors. This makes installing something like this simply plug and play.
I just installed a male connector to one lead wire from the potentiometer and a female connector on the other lead to connect it to my existing install :smile:
Below is a pic of the potentiometer which is actually a bit larger than actual size