Alarm System???
 

Twice now my 1981 911 sc has failed to crank while sitting in my driveway. I checked the voltage at the coil and this is none. The first time I had to push my car so that the front was facing the wrecker. The car was winched onto the flatbed, when it arrived at the mechanics it started no problem. today the car wouldn't start again and I had to push it again to face the right direction. I tried to start it again and nothing, but as the wrecker started to winch it I tried the ignition and it started. any ideas? I'm wondering if its something to do with the security system.
Thanks

Better castrate the factory alarm. Do a search here on Pelican, lots of info on how to do it.

I've never had a problem with a factory alarm. Fuel pump electrical circuit, CDI box, etc.

JR

Alarm.
 

If you fault isolate to an aftermarket alarm system, pitch it.

I can't tell you haw many members I've helped out on this exact issue.

Our factory alarm has never failed us.

Good luck,

Gerry

remove aftermarket alarms. i dont think the factory ones are that bad and may be harder to remove.
with an aftermarket system look for a relay that was installed in the start circuit.

sounds like a bad connection that is getting moved when it is put on the truck.

start with:
confrimed good battery. advance will check for free
CLEAN all major power connections. both battery posts, the ground strap to the body and the strap from the body to the tranny.
see what that does for you.

then i would look at the yellow wire connection at the battery. clean it make sure it is tight.
check the 14 pin connector at the rear relay panel and make sure all those connections are clean.

you can also check voltage at these points too.
i would work my way back to the ignition switch.
check and wiggle wires.

I chased a no-start gremlin for years. Turned out to be the ignition cut relay that was part of an aftermarket alarm. Got rid of it all, car works fine.
-C

I used to have to reach under the dash and pat all of the wires with an open hand to get the system to hook up and let me start.

System was installed poorly and it was evident what came out and what stayed.

It's been a while but pretty sure the mentioned yellow wire and it's signal to the starter is interrupted by the alarm system.