Crane Optical Ignition- what did I do wrong?

[Paul W]

Hi Guys

Tried to start my 3.2 earlier today after installing a newly rebuilt / recurved distributor, fitted with a Crane optical trigger to work with my existing MSD setup. Followed the instructions – red wire to switchable positive, black to earth and white to the MSD trigger wire (works through the MSD tach adapter).

Seems all pretty simple; wire it up, distributor in, turn the key – no start. Ended up plugging in a spark plug lead directly into the coil, plug in the other end turned the car over to see the thing fire half a dozen times before giving up.

Removing the distributor cap greeted me with the wonderful aroma of toasted insulation though close investigation showed no obvious sign of damage. Pulled the distributor, bench tested it and the Optical unit’s history.

So what did I do wrong? Red positive lead is spliced into the same lead switchable positive as for the MSD unit, the negative is spliced into the same earth lead as the MSD (wondered if this might be the issue??). Will take the distributor back to the people who did the work to sort it out but I'd be interested in any thoughts as to why this might have failed.
Thanks

[1976 TN Porsche]

Did you ever find out what was wrong.

[don gilbert]

I know what is wrong, he used the Crane system. I used to put these on harleys all the time back in the 80's. Very high fail rate, sometime rite out of the box. Never know when it will crap out on you. Just my personal exp. I dont trust them.

[moneymanager]

I had a lot of trouble with mine initially but it has run well for several years now. I tried first to run with only the optical trigger and could not get a straight answer about whether this could be done with the MSD. Apparently it can, but I ended up adding their box of electronics along with the MSD as I couldn't get the car to run without it. It was all very confusing. Crane first told me I needed their box along with the MSD then told me I didn't!
As to wiring, Crane said connect the three wire molex plug from the sensor in the distributor to XR700 box' molex connector. Three wires then leave the XR700: the red wire goes to an ignition switched terminal at rear which also has the red to/from the MSD. I used a 1.8 ohm ballast resistor so both the MSD & the optical trigger get reduced voltage. It straddled the red line from the Xr700 to the switched 12V source. The black wire is grounded & the yellow wire went to the white wire from the MSD 6. This sounds like what you did minus the XR700 which sounds right.
I was told that I didn't need the ballast resistor but that I should check the heat of the crane electronic box (called the XR-700 then, not sure what it is called now.) Mine was way too hot after 20 minutes so I added the resistor. If you should need a ballast resistor for some reason I don't think you'd find it out in the first few seconds. The heat buildup in my case took several minutes but that's just my experience.
Many people use the optical trigger only with good results. Steve Weiner on this board is one.