# Reversing polarity with 2 SPDT switches and 2 SPDT relays to control an actuator. .. #2

#### jhend1john

Joined Apr 21, 2022
5
from post #4:
Putting KISS's description into picture form :-
View attachment 107979
Note that a Bosch relay may include a diode across the relay coil, so polarity of the coil is important. The internet has conflicting views as to whether pin 85 or pin 86 should be grounded. Pin 86 should go to ground (as I show in the above pic) if the diode anode is connected to pin 86. Check the resistance between pins 85 and 86 to determine the diode polarity.
If the diode anode is connected to pin 85 then the wiring would be like this :-
View attachment 107983
This item refers to the possible diode presence.
If your actuator moves the wrong way when a pedal is pressed, just reverse the two connections to the actuator.
What does the circuit look like if there is just a resistor between 85 and 86. There is about 100 ohms when I measure across 85 and 86 in either direction.

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#### crutschow

Joined Mar 14, 2008
30,098
What would happen if both switches were pressed at the same time? Wouldn't I be causing a short?
No.
With both relays actuated, 12V is applied to both motor terminals, so there is no current through the motor.
Where would there be a path for a short?

#### LowQCab

Joined Nov 6, 2012
2,169
Also keep in mind that a "Linear-Actuator" is only going to be able
to turn the Motor about ~160-degrees,
so You will need provisions for reversing the Main-Propulsion-Motor
since You can't turn it all the way around for Reverse.

You also need Speed-Control for the Main-Motor.
.
.
.

#### Alec_t

Joined Sep 17, 2013
12,889
What does the circuit look like if there is just a resistor between 85 and 86. There is about 100 ohms when I measure across 85 and 86 in either direction.
That implies there is no internal diode in the relay, just the relay coil. It would be advisable to add an external diode (anode grounded) across the relay coil to suppress the back-emf generated when the relay coil is switched off.