Push Button Start

[porscheboy1]

Hi Guys,

On my 1978 911SC, concerning the ignition/starter switch. I have replaced the electrical part with a new one and all seems to be well there. The mechanical side is not so healthy after 200,000 + miles. When I put the switch over to the start position sometimes the starter is energized and sometimes it is not. With a lot of fiddling with the key it will finally work. To avoid getting stranded away from home by a no start situation I am thinking about installing a push button switch under the dashboard to run the starter. On the starter switch I could run a wire from the always hot terminal 30 to the yellow wire at terminal 50 with the push button switch in between. With the plug in connector on the back of the switch how would I find the red and yellow wires? Strip the sheath off behind the plug, or is there another way? What brand and size push button switch should I buy and what gage wire should I use?

Cheers,

Johnnie Pete the mad Swede

[75 911s]

Sounds kinda cheesy and a possible fire hazard. My buddy had a push button start in his 80's VW rabbit for the same reason.

What about rebuilding the mechanical side or picking up a used one?

[psalt]

Most starter problems are really battery problems, first check out your battery or substitute a known good battery. I have had the same symptoms and if you charged the battery for a minute before attempting to start, it disappeared. My experience is BOSCH starters die with intermittent starting, sometimes the solenoid, sometimes not, which is why BOSCH rebuilds sometimes are short lived. The rebuild process often does not touch the real problem. The cores are now all over 20 years old. I always recommend the gear reduction starters for this reason.

First I would wire up a volt meter from the yellow solenoid terminal to see what is actually happening when you turn the key and nothing happens. Are you getting 12 volts to the solenoid ?

The proper way to wire a push button is with a relay at the starter, then one wire up to the dash, and a push button to ground the relay coil. Cost about $20 and very easy to fit. Since the 911 starter is so hard to get at when in the middle of the road, I installed a remote button near the oil tank. Nice to have for valve adjustment/distributor removal/etc. You do however have to remember not to hit the button with the car in gear when there is no one in the car.

[Larry Marshall]

There is a procedure on this forum to install a button start. I used it a few years ago to install one in the front and one in the rear by the fuse panels. I was in the process of a complete re-build (3.2) and was having no start difficulty. I used them to activate the starter from a position that allowed me to see what was going on in the engine compartment or the front bonnet. The process uses a simple relay and lays out the specs for wiring. I added a simple toggle switch for the hot wire at each button switch to eliminate fire hazard. Search this blog and you'll find it. Hope this helps, worked great for me. Larry

[911pcars]

Did it for my '69 years ago. Saves wear and tear on the crank portion of the NLA ignition switch.

Remote Starter

Sherwood

[Luccia at Pelican Parts]

Originally Posted by 911pcars

Did it for my '69 years ago. Saves wear and tear on the crank portion of the NLA ignition switch.

Remote Starter

Sherwood

This is great. You should submit this to our customer content DIY articles here.

[porscheboy1]

Thanks for all of the info. After reading all the posts and their references I determined that the disc in the back of the tumbler on the mechanical side of the switch was not always re setting the switch when going to the off position after a start and hence the start position was locked out on the next try. I had sprayed some graphite into the lock previously. This time I sprayed in WD40 and it freed up the mechanism almost immediately and everything works. I still will install a remote start switch per the diagram that "911pcars" presented in his post, all properly fused.

Cheers

John

[911pcars]

Originally Posted by psalt

Most starter problems are really battery problems, first check out your battery or substitute a known good battery. I have had the same symptoms and if you charged the battery for a minute before attempting to start, it disappeared. My experience is BOSCH starters die with intermittent starting, sometimes the solenoid, sometimes not, which is why BOSCH rebuilds sometimes are short lived. The rebuild process often does not touch the real problem. The cores are now all over 20 years old. I always recommend the gear reduction starters for this reason.

First I would wire up a volt meter from the yellow solenoid terminal to see what is actually happening when you turn the key and nothing happens. Are you getting 12 volts to the solenoid ?

The proper way to wire a push button is with a relay at the starter, then one wire up to the dash, and a push button to ground the relay coil. Cost about $20 and very easy to fit. Since the 911 starter is so hard to get at when in the middle of the road, I installed a remote button near the oil tank. Nice to have for valve adjustment/distributor removal/etc. You do however have to remember not to hit the button with the car in gear when there is no one in the car.

Diagnosing electrical circuits requires specific diagnosis rather than relying on common/historical solutions - much like replacing parts instead of pinpointing the real source of a malfunction.

Measuring available source voltage at the load (light bulb, motor, etc.) is a basic troubleshooting technique, and it works for most circuits. However, the no. 50 yellow wire from the ignition switch is only used when cranking the engine.

When measuring cranking voltage at the battery, one notices it drops as the engine cranks (e.g. 12V > 9 or 10V), and thus the same voltage found at the starter solenoid during cranking, >9 volts, but never 12V due to the voltage drop as a result of the starter motor cranking the engine.

A relay mounted near the solenoid reduces the existing current path (by about 6'). This minimizes voltage drop (while maximizing source voltage) to adequately energize the starter solenoid. As I mentioned in my earlier post, the added relay also increases ignition switch life by minimizing current through the normal "cranking" contacts of the switch.

Sorry for any redundancy.
Sherwood