I picked up a small tach which I'd like to install in my 93 240. The tach has some wires on the backside which were clipped off to remove it from the donor car. The top two are for the light....should one of them be grounded? The bottom 3 wires I'm not so sure about, other than they power the tach itself. What/where should these wires hook up to? In a question not to far below on this list, I asked about a red/white wire behind the instrument panel that isn't hooked up to anything. Is this wire part of the answer to my question? Oh, one more question: this little tach has lots of film on the backside of the dial glass. How does this thing open up so I can clean the backside of the glass? I tried turning the black bezel ring, but that's all it does..turn. Is the ring crimped on somehow so it can't be removed at all? Or should I use my bottle cap remover? ;-) Thanks for your wisdom!

i actually did this a few weeks ago. there are two wires that connect to the light capsule thing. THe black wire you need to ground it on anything metalic. I simply found a screw underneath the dash, loosened it and tightented it with the wire there. THe other light (trickiest light to hook up) needs to be spliced into one fo the brown power lights which turn on when you turn on the lights at nighttime. This can be wired either into the brown light dimmer switch behind the dash or a fuse which goes live when you turn on the lights. The third possiblitity for the light wire is behind the central console for those lights which are on at nights on the a/c. THe red/white wire which you mentioned as having found is the tachometer wire which goes to the coil. THis you simply connect to the tachometer wire, which is found dangling loose behind the dash. THe last wire is the power wire for the tachometer which must be spliced into the fuse box. THere are terminals for this in the fuse box and typically 11 and 12 are goood choices for this.


IF you have any other questions please ask.


btw...if you bought an old tachometer/used, then the light is probably burned out....i'd look for a new one if so:)

I just realized that I needed to provide some more information on this question. The 3 terminal at the bottom of the tach are G, +, and -. The red/blue wire is hooked into +. There is a black wire leaving G. There are 2 black wires leaving -. One goes up to the clock and the other is clipped. The clock has two terminals: one has the a black wire coming up from the - terminal on the tach. The other wire is a clipped white one.

Does it work this way?: red/white (+) needs 12v power from fuse block terminal #13, black (G) goes to ground along with the white from clock, and clipped black on (-) can tie into the red/white wire behind the instrument panel. ??????

And I still can't figure out how to remove the dial glass......

as I recall the "g" gets the red and white wire. the plus gets power from a swithced fuse. and the negative is the gound. that is splice of the ground of the light. The other wire on the light needs to be spliced off one of the brown wires behind the dash. I had an extra one that I used.

Good luck and happy bricking.

Thanks guys. I think I got it. I'll repeat: The G terminal at back of tach is where the red/white "mystery" wire behind the instrument panel connects. The (+) terminal backside of tach gets power from a fused 12v power source. The (-) terminal backside of tach connects to ground somewhere behind dashboard. Power to the light comes from the dimmer switch on dash. Ground the other light terminal same place as tach is grounded.

If this is still incorrect, please let me know .

yeah bro you pretty much have it. What i did exaclty was i hooked up the 12v power wire for the tach to terminal 12(whatever fuse is on when you turn the car on...so fuel pump fuse works great) in the fusebox, the light wire to terminal 14(this was the headlights terminal fuse pretty much), the ground wire(black) i loosened a screw and simply tightened it with the wire(under the dash) and the tachometer signal wire went to the lone wire found loose behind the dash.

have fun:)