bmwe21.net forums

my car is a US model '83 320I. those of you who have seen my thread in the owner's gallery know that it has a Mazda 12A rotary under the hood. I've been driving it around with no tach for over a year, and I was looking at my spare one, and it looks like I should be able to make it work, but I don't know which wire does what. The wires I believe I am to use (since there is stuff for a clock and all that on there (not going to use that) are the 3 wires on the wide flat connector (tecnically 4 wires as there are two coming out of one spot... but they act as one I'm sure.

So, if one were to be looking at the back of the tachometer, the two wires coming out of the far left part of the connector are brown, there is a "31" etched in the plastic above it. In the middle is a black wire, and there is a "1" etched in the plastic above it. one the right is a purple wire with an "R" etched above it.

to the right of that connector I just mentioned, is another connector that has two wires, a gray one with a white stripe, and a red one with a white stripe... don't know what those are for... the one on the bottom right looks to be for clock stuff, so I'm not going to worry about that unless you guys say otherwise.

I have discovered through RX7club.com that any 4 cylinder tachometer should work for my rotary, and I've found how to wire a tachometer, but it doesn't say how to re-wire a BMW tach to a bastardized car like mine, so I don't know which wire does what. Anyways, I figured it was worth a shot to ask on here, please let me know what you know, thanks!

in the engine bay on your stock loom there would have been a very thin black wire, this is your rev meter wire.

shame the stock rev meter doesnt go up to 9k! and no red line buzzer!

Thanks! I found the thin black wire, it runs to the fuse box right? the wiring harness that came out of the fuse box and towards engine wizardry is long gone, so I'm really hoping you mean that thin black wire I found before the fuse box.

So, I could basically hook that up to the negative terminal on one of my coils and my tach would work? I figure the ground and switched power would be taken care of already seeing as how I never touched the tach wiring on this car... besides all the wiring after the fuse box.

I'm really looking forward to having a tach on this car, it would be kind of funny if it really were that easy after all this time of not having one.

and yea, it is a bummer that the tach doesn't go higher than 8k, but I've heard that 8k is about as high as a nearly stock 12A would want to go anyways... I might end up pegging the E21 tach... I have a spare, so whatever.

yep thats the boy, thin black wire - fuse box.

happy to help ya. i dream of rotorising an e21 one day with a 13b RE bridgy turbo. i even have a freind selling a set of BNR twin turbos. he ran an easy 400HP on stock ports instant power any revs.

its money though, turbos alone are a thousand pounds. *sigh* I miss my rotors bro.

Sweet! thanks again! Glad to see another Rotary lover on here!