911 1969 Sportsmatic not cranking the engine

[boofs]

Hi,
911 1969 Sportsmatic not cranking the engine, there is 12volts at the ignition switch which switches it ok, 12volts to the yellow lead which should go to the starter motor solenoid via an isolator switch and a connector but there is no 12volts at the solenoid the isolator switch on the gearbox which I have replaced new but still no 12volts at the solenoid, I have run a lead from the ignition switch to the solenoid and the engine cranks ok, has any member had this problem or have the wiring diagram for the sportsmatic isolation circuit as the manual show direct connection from ignition switch to starter solenoid with just one connector in-between,
Regards.

[MrJTP2001]

Ok, basics. Transmission must be in PARK, maybe NEUTRAL depending on year. There are two switches on the transmission which monitor position of gear selector. If either of these switches is not in the correct position the 12 volt power to the starter is interrupted. The pins on the transmission switches are fragile and may visibly appear to good while not actually working.

As far as a schematic goes. I have never seen an "integrated" schematic showing how the Sportomatic electrical circuits blend together with the rest of the vehicle electrics. Yes, I do have the workshop manual but it is little help in this case. I'll include a pictorial diagram of the Sporto system from the manual to give you an idea of how it works.

Got vacuum?

[boofs]

Hi thank you MrJTP2001 for your reply, I have replaced new both these switches in the sportsmatic gearbox but it has made no difference and when I checked the switches I had removed from the gearbox they checked out Ok,
Regards,
Tony, Totnes, UK.

[edmayo]

I don't have a ready answer for you other than this is where you start at the battery and using a volt/ohm meter start checking the entire path of the start circuit from beginning to end, and when you find the problem I'll bet it will be a very simple fix. If the car came to my shop this is how you go about diagnosing problems. Experience will only let you zero in on the most likely culprits, if those aren't it then it gets down to detective work.

[boofs]

I made up a tool from a spark plug and bolt for checking the tdc and it confirmed Z1 mark as tdc,
but still it will only run and start good with the tick over set to 30 or 35 degrees btdc which means at 6000rpm it is 45 or 50degees btdc I do not no what to do next to get it as the manual states ?.

[boofs]

The problem was simple in the end it was a faulty crimped connector on the two yellow leads that run from the bypass switch to the starter motor solenoid and the backup light switch it is located up near the starter motor.

[edmayo]

Thanks for the report, as I said it's often a simple fix, it's just trying to find that point for the simple fix that drives us nuts!

[boofs]

Thank you edmayo for your help