108-2 Ignition Switch and Magneto Connection

“Delco Remy” remains a registered trademark of General Motors Corporation, however, the ignition switch for the Stinson is considered obsolete by them. The Delco Remy part number for the switch is 1994524. You can find them on E-Bay occasionally.

The “P” in P-lead originates from the primary winding within the magneto’s coil. To disable the magneto, the primary winding is connected to ground. The ignition switch controls the opening and closing of the P-lead circuits to aircraft ground. Within the internal mechanism of the Off/L/R/BOTH ignition switch lie the necessary connections. When set to OFF, both the left and right P-leads are connected to ground, deactivating both magnetos. In the L position, the right P-lead is connected to ground, while in the R position, the left is connected to ground. Selecting BOTH opens both P-lead circuits, activating both magnetos. Without P-leads, both magnetos would remain energized continuously.

Back side of the Stinson Delco Remy Ignition Switch, p/n 1994524

For Fritz’s Stinson 108-2, the following wire numbers coincide with the connections on the back of the ignition switch

Ignition Switch ConnectionWire Number
GRDAIRCRAFT GROUND, P-Lead shield wires
START7 (Starter switch to starter solenoid)
BAT8 (Starter switch battery terminal to power bus)
LT MAG (P Lead)16 (Starter switch P-lead to left mag)
RT MAG (P Lead)15 (Starter switch P-lead to right mag)
Wire connections
Ignition switch wiring diagram

OFF

With the ignition switch in the OFF position, the left and right P-leads are grounded, and both magnetos are off.

LEFT

With the ignition switch to the L position, the right P-lead is grounded and the left magneto is on.

RIGHT

With the ignition switch to the R position, the left P-lead is grounded and the right magneto is on.

BOTH

With the ignition switch on BOTH, both P-leads are open and both magnetos are on.

Troubleshooting the Switch

Using an ohm meter, jumper between the pins on the back of the switch with no wires attached. You will either get an open or a short, depending on the switch position.  See the chart BELOW for correct results.

SWITCH POSITIONCONTACTCONTACTRESULT
OFFGNDBATOPEN
OFFGNDSTARTOPEN
OFFGNDLEFT MAGCLOSED
OFFGNDRIGHR MAGCLOSED
OFFBATGNDOPEN
OFFBATSTARTOPEN
OFFBATLEFT MAGOPEN
OFFBATRIGHT MAGOPEN
OFFLEFT MAGSTARTOPEN
OFFLEFT MAGRIGHT MAGOPEN
OFFRIGHT MAGSTARTOPEN
SWITCH POSITIONCONTACTCONTACTRESULT
LEFT MAGGNDBATOPEN
LEFT MAGGNDSTARTOPEN
LEFT MAGGNDLEFT MAGOPEN
LEFT MAGGNDRIGHT MAGCLOSED
LEFT MAGBATGNDOPEN
LEFT MAGBATSTARTOPEN
LEFT MAGBATLEFT MAGOPEN
LEFT MAGBATRIGHT MAGOPEN
LEFT MAGLEFT MAGSTARTOPEN
LEFT MAGLEFT MAGRIGHT MAGOPEN
LEFT MAGRIGHT MAGSTARTOPEN
SWITCH POSITIONCONTACTCONTACTRESULT
RIGHT MAGGNDBATAOPEN
RIGHT MAGGNDSTARTOPEN
RIGHT MAGGNDLEFT MAGCLOSED
RIGHT MAGGNDRIGHT MAGOPEN
RIGHT MAGBATGNDOPEN
RIGHT MAGBATSTARTOPEN
RIGHT MAGBATALEFT MAGOPEN
RIGHT MAGBATRIGHT MAGOPEN
RIGHT MAGLEFT MAGSTARTOPEN
RIGHT MAGLEFT MAGRIGHT MAGOPEN
RIGHT MAGRIGHT MAGSTARTOPEN
SWITCH POSITIONCONTACTCONTACTRESULT
BOTHGNDBATOPEN
BOTHGNDSTARTOPEN
BOTHGNDLEFT MAGOPEN
BOTHGNDRIGHT MAGOPEN
BOTHBATGNDOPEN
BOTHBATSTARTOPEN
BOTHBATLEFT MAGOPEM
BOTHBATRIGHT MAGOPEN
BOTHLEFT MAGSTARTOPEN
BOTHLEFT MAGRIGHT MAGOPEN
BOTHRIGHT MAGSTARTOPEN
SWITCH POSITIONCONTACTCONTACTRESULT
BOTH WITH BUTTON PUSHED AND SWITCH ADVANCED TO STARTGRDSTARTCLOSED
BOTH WITH BUTTON PUSHED AND SWITCH ADVANCED TO STARTGRDBATOPEN