Start Buttons

Having had a quick look through the search engine and not finding an obvious answer I would like to pose the question to those more knowledgable than I about the ubiquitous start buttons sometimes seen in cars.

My question is basically aside form historic accuracy, what is the purpose of the start button when a regular key based ignition would seem to work just fine? And speaking of historic accuracy, why did these cars have them in the first place? Was it easier to start, more reliable? And now, why do modern cars (usually high end sports cars) have a start button and some not?

I am sure someone will know the answer, and I would also love to know as it intruiges me greatly.


Image if you

lost the keys prior to the race
picked up your wife's keys by mistake
broke the key while trying to start the car

The start button is fool proof.
I thought yo ustill needed to turn the key in the ignition anyway. If I recall thats what Tiff Needall (sorry if last name spelt incorrectly) did on the GT40 video. Key in, trun, then press the start button.

Actually I would be somewhat disturbed if I owned a GT40 that could be started by any old key. Also, I should probably add that when I say disturbed, I actually mean - more disturbed than I already am.


you don't necessarily need a key switch, just a continuous switch to turn the electricals on. The push button just energizes the starter solenoid. You can do both functions with a single switch (keyed or not keyed) or with two switches (one must be a continuous connection and the start a mometary). I personally like the push button mometary - it's fun. On one of my other cars the start is a momentary toggle switch. I like it too. Just personal preference.


Doc Watson

Lifetime Supporter
As Mike said, the key usually turns on the electrics which includes the fuel pump system, once the fuel is up to pressure the start button is pressed to power the starter. I assume its used to allow a second or two for the fuel to pressurise. They are cool though.......


Russ Noble

GT40s Supporter
Lifetime Supporter
Andy, you can achieve exactly that scenario with a conventional key start. You just wait til the pumps pressurise and turn the key.

I think Bill D is on the right track though with his answer.

Thanks Russ :)

If you look closely in this picture, you will see a guarded OFF-ON toggle switch. That switch turns on the car's power, similar to turning the ignition key to "ON". Next to the guarded switch you will see a red momentary OFF-ON pushbutton switch. That is my "START" switch.

The wiring is different as night and day for the two systems. In a keyed ignition the power to the stater is the last position on the "ring" and is "equivelent" to a momentary switch(only activated when selected). Those that use the start button have to have a relay that the start button acvtivates. In a relay there are two ciruits. The main power(high current) and the coil(low current) that activates or controls the main power and keeps the high current away from the delicate switch. The push button activates either the coil or the ground to the coil, depending which way you wire itl Either will work. The coil is basicly a magnet that causes a jumper to close the main power to the starter. Once the start button is released, the coil is deactivated and the power to the starter is broken or stopped. Sometimes a diode is used between the coil and the ground to keep the spike of power from traveling back up the circuit and damaging sensitive electronics.
It took me a long time to understand how they work. The relays can be tied together to do just about anything you want electrically speaking. You can make things start, stop, energise or deenergise, whatever, car alarms, starters. door openers.......... and so on. I am using two relays just to control the other 8 relays!!!!!


Bill Hara

Old Hand
GT40s Supporter
Bill D, that setup look great, but the question arises - do you have a kill switch on a key fob or something similar to stop someone stealing your beautiful car?
I would hate to think it is that easy to just jump in and start up without some other personal method of security.....

Bill H
I have a slightly different idea about the start button. On my last car I used the push button to build oil pressure in the block, then turned the key and hit the button again to start the engine. Oil is a big deal and I have always heard that most engine damage is done on start up so you need to build pressure before ignition. Just my $.02!