912ULS ignition switches permanently earthed

by Kev in 912 / 914 Technical Questions 12 years ago

Both terminals, on both ignition switches, indicating earth, regardless of switch position.
Problem had previously occurred, but cleared again without my being able to find the cause.
Switches and wiring confirmed seviceable up to ignition module 6-pin plugs ie with plugs disconnected, p-leads not earthed with ignition switches 'on'.
When plugs connected, p-leads earthed with ignition switches 'on'.
Unable to find any signs of wires chafing (and picking up an earth)around or under ignition modules.
Any suggestions gratefully received.

Kev

Re: 912ULS ignition switches permanently earthed

by Roger Lee » 12 years ago

Roger Lee

128 5.28k 4.98k

You may have wire insulation that has chafed through and are now touching something. Check all the wires from the 6 pin plug back. It may be only a small chafe, but it it is touching metal it is grounded.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: 912ULS ignition switches permanently earthed

by Kev » 12 years ago

Kev

2 13 0

Have been away for a while, hence the delay. There is good news and bad news.

Bad news first - Ignition switches operate normally (ie off-grounded, on-open circuit) with ignition modules disconnected, and similarly with modules connected to ignition switches but not connected to coils, but with all connected, switches are earthed in both on and off positions.
Module wires and terminals inspected - no sign of any damage or chafing.
Coils wiring inspected - no sign of any damage or chafing.
Curiously, with all plugs connected, but the coil earths (2x) disconnected from the LH intake manifold, switches operate correctly.

Now the good news - not sure why, but I reassembled everything (but with the earth problem still apparent) and pulled the trike outside, just to confirm that it wouldn't start. Turned it over, and it started! Shut down, then checked the switches again - earthed on both switches for on and off positions. And yes, I did check that I was on the correct terminals.

So now I'm completely baffled. Have I just been chasing my tail all along? If anyone can offer an explanation (for dummies) as to what may be happening, I would be very grateful.

Kev

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912ULS ignition switches permanently earthed

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