the 911 parts car tach was not working when we ran the motor...any suggestions on how to test it now that the motorand tranny are out of the car
thanks
steve

For bench testing I built a 555-timer circuit with rotary switch to select calibrated rpms from 1000 to 6000 (1000 rpm increments) and correction for dwell. This drives a relay connected to an inductor to simulate the typical ringing waveform off a coil ignition. This works out really nice but requires some skill to build the circuit and a scope comes in handy to debug it.

Without a signal source such as the above, your easiest method is to borrow another car with a points-type or coil ignition system and hook your tach up to it. Or, you can get a distributor and figure out a way to spin it with a drill, then wire it up to a coil and battery.

By the way, I'm assuming it's an older 911 with a tach similar to those in the 914.

the tach is out of a 79 911 sc

Guy,
Can you post/send a schematic of the bench test circuit? I would like to test some tachs as well.

Thanks
Paul

My guess is that it uses a similar VDO tach hooked to a coil, but breakerless ignition. I'd think you could test it on any 12V coil ignition system.

QUOTE (Phoenix-MN @ Oct 18 2005, 12:14 PM)

Guy, Can you post/send a schematic of the bench test circuit? I would like to test some tachs as well. Thanks Paul

Paul, let me look this evening when I get home. I know I drew something up on it and hopefully didn't throw it away by accident. I'm sure it's buried somewhere on my workbench.

The SC tach runs off the CD box, so you MAY have a problem using it with any other system. The Cap'n

what is the cd box...

QUOTE (pete-stevers @ Oct 18 2005, 01:20 PM)

what is the cd box...

The ignition control unit. Commonly called the Capacitive Discharge Ignition. BHKZ if you're German. The Cap'n

capacitive discharge box