wtf is there a ghost in my wiring?

[gasman]

when ever i turn on my dash lights my tacho stops working.
i just cant see why it would do something like that.
the car is a ae92 fxgt with a 4agze engine. using the mitsi tach interface with the inputs as the feeds from igniter to the two coils and the output straight to the tacho.

[Ae92typeX]

havn't changed the earth source at all?

[nz_climber]

or the dash lights are drawing power through the interface thing to the mitsi coils (or off the tacho), so it shuts down(from too much current draw) and stops working... either that or the earths

[gasman]

all the earths seem to be connected and looking at the back of the dash itself the tach feed from the igniter goes straight to the tach its self and nowhere else so the lights cant possibly be drawing from them as they have their own seperate circuit.

could the tach it self be bung?
anyone else have this problem before?

[KinLoud]

I have seen a similar problem where a different fuse had blown and something else failed but it also affected something that should have been on another circuit. I figured it must have had a small earth potential difference - just enough to drop the voltage so it didn't work.

Ken
Ham
021 408 863

[gasman]

somthing really weird is going on.
using an aftermarket tacho with the signal fed from the 4agze ignitor output and tacho set to 4 clyinders the aftermarket tacho works fine with the lights on and off. but since 4agze is dli shouldnt the aftermarket tacho read half of the actual rpm's?

when i try running the aftermarket tacho with the vr4 tacho interface it doesnt work, or if i try running the aftermarket tacho off the back of the dash using the original wiring the aftermarket tacho stops working when i turn the lights on.

so now i try running the dash tacho with independant wiring for power and signal it still doesn't work when the lights are turned on.

[KinLoud]

Try giving it a separate earth for the tacho

Ken
Ham
021 408 863

[hsmidy]

yeah man i had a similar problem not a toyota(vs commodore) but yeah turned out to be a bad earth at the battery everything thing else worked fine but as soon as the lights went on the rev counter stopped, just make sure ya terminals arent loose or anything electrolyte levels etc