I swapped out my carb this weekend to one with an electric choke and need to find a place to tap into ignition on power for it. I thought I could use the coil but when I hooked it up it wouldn't start. I really don't want to have to snake a wire all the way up to the dash to tap into something, but my mind is drawing a blank as to what else around the engine would be a power source only when the key is on.

Purple wire is powered with the key on.

you dont want to use the purple wire to open the choke tho..you can trigger a reley to the choke wire,,just loosen the choke reastat and open it all the way..you really dont need a choke for summer..2 pumps and they start 99.999 % of the time..

The alternator should have a switched + wire off the back. Sorry, can't remember which color it is right now.

Ayuh,.... Mercruiser has been usin' the ignition circuit to power the choke, since the invention of the electric choke,....

The ignition circuit is the purple wires,...

Correct...but you do not want to wire the choke directly to the terminal on top of the coil. This is a no, no. Just like the thread starter's issue, I have seen way too many boats with starting/running problems with accessories hooked up the coil terminal.

If you must run a choke follow FIXX's advice. An electric choke has a fair draw, its a direct short.

here's a typical 5.7 tbIV wiring diagram with electric choke. Note, it is the same purple wire as mentioned, however, it's not right at the coil. Again, I've seen issue's when most things are connected to the coil terminal itself.

Click on following if you can't read attached pic:
http://www.marinemechanic.com/site_i...-IV-WIRING.gif