wire that shows + or - when running

I have someone asking me to wire in a basic push button starter on their car. Basically the key will still control ignition, accessory, and unlock the steering column, but I will be cutting the starter wire and using a relay powered off of whatever button he has. My question is, is there a wire in the car that shows either (+) or (-) ONLY when the car is running? This will help to cut power to the button once the car is running and prevent accidental over-crank if he sets something onto the button.Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

All I can think of is either a latching relay off the starter wire, or a 528t or 611t set for what 20 seconds? a minute? And I think the timer is the easiest way and I haven't smoked any funny ciggies. Sorry for sounding so pompous before, I was having a laugh.

Just buy a UIBI... (LOL!) The alternator charge light circuit (ie, D+ or L) is the traditional oft used "engine running" signal that "master" controls things like fuel pumps, fuel cut-offs, electric chokes, etc. (Oh, and aux-battery isolators - how could I forget!) However EFI/EMS has changed some of the above - ie, they now control pumps etc. But those vehicles often still have alternators with a D+ or L. Newer EMS controlled alternators may not have that equivalent output, but it should be possible to sense the others (using electronics with filtering). I was going to suggest the pulse (spark) sensing relays that VAGs use (for fuel pumps etc) or maybe air-flow sensors or air-flaps, but these will register whilst cranking so some form of discrimination must be used - ie, the difference between cranking and running. Plus those relays have an initial on time (to prime the fuel) before any spark is sensed. (But a spark/pulse sensing circuit that switches above cranking speed is possible.) Air flow & flaps are probably unsuitable - they'd need a lock-out during idling & low speeds etc. And whilst it's easy to disable those signals during cranking, that is NOT what you want. Maybe starter-current sensing - ie, >100A is cranking. I guess I'm back to an alternator signal - provided the alternator doesn't signal during cranking. (I had a recent alternator whose charge light extinguished during cranking, though later that circuit did prove to be faulty. But I wonder if some could be so sensitive so they detect the generated voltage during cranking.) Then there are the OBD etc signals... But I'm merely suggesting "simple DIY alternatives". (Howie's timer or alternator charge signal.)

yea, I ended up just going with the button for now (recessed and vertical, where it hopefully will not have any ability to be pressed accidentally). And I think I will eventually end up putting the timer in there for him down the road. But still, thank you for all that information oldspark... you are crazy when it comes to that kind of electrical... haha.Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

How dare you be so discriminatory! I'm just plain crazy! But thanks for the thanks. (And yeah, those "simple and superior" solutions were so much easier in ye olde days - all cars had an "engine running" signal (D+ or L). It's due to modern technology I have to ramble...) Cheers!

And you know Uncle Howie, always looking for the KISS solution, usually more reliable! By the way, make 86 on your relay ignition 1 controlled, that will obviate half of the problem anyway.

Yes, I made 86 ignition and grounded 85 through the push button. That way its only enabled when the ignition is on. I'm hoping he'll eventually go for the timer relay which will make things a little nicer and a little more secure. The only downside was that the installer who put the alarm/remote starter in left me no room on the ignition harness to tie the new wires into. But I pulled the tape off a few connections, found that they were soldered and appeared to be solid, then tied into the alarm / r/s wires just before the ignition... so it should be fine.Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

Kenny, I don't know which post this was but I just did a proper coil draw test on a Bosch style cube relay, 150 milliamps so apologies all round. The obvious reason (well obvious with hind sight) was what ever the SWITCHED side was drawing was what flattened the battery. Got to apologise to Kregg now.