Originally Posted by Drippy
I believe my bendix mag failed but wanted to ask for advice before shipping it down to tropic airpower for another rebuild.
I have 5 hours in the air and everything has been performing well, but today when I performed my Mag check prior to take off the mech mag failed. For info I have one non-impulse Bendix and with a light speed electronic.
I checked my P-lead and checks good in both key positions (off and selected). I noticed that the mag body was grounded so had someone spin the prop and noted it remained grounded throughout rotation after removing the ground wire and P-lead.
Next idea was points were not opening - so removed the mag back cover and rotated mag and confirmed points were opening. Checking conductivity across the two terminals it never dropped even with contacts/points open.
After messing around and with the help of a hangar mate A&P we figured out that the wire to the coil was constantly grounded. The question is "this isn't suppose to be grounded right? and this means I need to return the mag?"
To clarify this is the one wire that goes from the mag coil to the points connector.
A couple of thoughts:
1. It is very dangerous to not have the pLead grounded while you are pulling the prop through (i.e you have a hot mag) unless you have all the plugs out. More than one person has been killed doing this.
2. A coil that has one end connected to ground will read a low resistance on the other end, as in just a few mohms. Check that you are on a very low scale on your multi-meter.
3. The mag body is connected to the engine - which is grounded.
4. If you only have 5 hours on this rebuilt mag, call the place that did the work and ask them.
5. Do not rule out your ignition switch. Using it with a mag and a Lightspeed you could have wiring problems.
6. Did you do the timing check? Remember your mag is set at 25 degrees BTC and your Lightspeed is set at TDC (assuming your are running a stock 260hp IO-540).