Mag problem - please help

[Alpha]

Help please...

I have an awesome 503...but lately i have had a problem and it escalated this weekend! She starts perfectly, idles great and runs loke a dream, however when it comes to switch mags off, i get the problem where she still fires..

On saturday, i did mag checks...all ok then when i parked and turned mags off...nothing...engine still ran...i had to kill motor by opening chokes...

Did a restart and the mags off and the engine died normally...

Where do i start, mags, ht cables, toggle switches?? Any help would be greatly appreciated.

[Bundy]

Sounds like a earthing prob to me Gary?

But let the experts advise you better...

Hope it's not too $$$

This weekend you will get all the answers you need at FABA

[KFA]

Check the ground wire on the mag switches. If that is all OK then replace the switch. The motor is cut when the mag wire is gounded. It was designed that if something goes wrong with the switch or wiring then the motor will keep on running.

[Morph]

Does this happen on both mags, i.e. if you switch right first instead of left and vice versa.

Do you do mag checks before flight, this is critical? If so, are you seeing the rev drop on either side when you do the test?

If you do see it on one side only that narrows your search

Using a piece of wire, start the engine, switch the good mag off, and then short between the engine side of the switch and a good earth on the chassis, does this cut the motor? If so, the problem is between the switch and earth, connect the wire to the other side of the switch and on to a good earth, now switch off, does the motor cut? No then it is the switch that is faulty, yes then it is the earth the is bad, probably corroded.

If the problem is on both mags, then it is the common earth that both switches are going to.

[Alpha]

Hey Morph,

Glad to see you back. Well to answer a few questions, a mag check I always do before take off...no problem...however, when I landed....switch both mags off...intermittent firing, same as when I switch one or the other off independently.

Also...if I switch both off....motor runs unhindered...so I am presuming it is an earthing problem, with the common earth. Does anyone have a wiring schematic for the mags listing wire color etc?

[Tailspin]

Hi Alpha

Definitely an Earthing Problem.
Need to check all cables are still connected and good.

[mulderpm]

Alpha, I had the same problem. The earth wire in the console on the back of one of the mag switches became dry joint/lose. When you kill the mags on the ground she carries on running on one set of mags. When you have the console open, check all the connections and tighten the terminal blocks. Taxiing seems to shake the wires lose.

[Morph]

Here is the wiring of the motor

Connector 8 is the one we are looking at