@Tonyr1084 yes. Nice Diagram. Finally, someone paying attention to polarity.

Credit goes to @LesJones for polarity. I tried to find information on @813mariner's relay but didn't find anything definitive. I will now endeavor to remember that pin 86 is generally going to be the positive post of the coil.

 

Surprisingly enough, the automatic system That can be purchased seperately for this set of tabs has an auto retract feature when the key is turned to the acc. Position for 5 secs. as a safety feature, regardless of position. So if the tab is fully retracted to begin with, thats 5 seconds of run time with actuator bottomed out. Cant be good for them !

Car electric window controls manage to fully lower or raise windows without overloading the motors. Maybe there's a current sensing circuit that can tell when the motor has reached an immovable obstacle and cuts power. Maybe the commercially available control has a similar feature. Waiting five seconds may be just so the tabs can be fully retracted IF they are in a fully deployed state. Such high end stuff is nice, but with a little care a user can operate a system and not damage anything if they're paying attention to what they're doing. The real problem comes when you allow someone else to operate the equipment and they are not that savvy.

[edit] If you want to - you could build in a current limiter so that when the motor reaches full deflection the current a stalled motor would draw will prevent overheating.

I had a truck with a bad fuel pump. It would blow the fuse. The pump would run for a few seconds at a time. I just happened to have a 20 amp self resetting fuse, which would allow me a few seconds of fuel pressure so I could drive the truck up the driveway and into the garage for repairs. I'm thinking if your motors typically draw (oh, lets say) 3 amps to run and possibly 9 amps when stalled, a 5 amp self resetting fuse might offer the protection against burning out the motor if the button is held too long after travel limit has been reached. I wouldn't DEPEND on that but in the event someone unknowingly hit and held the button too long the breaker would trip. When it cooled it would again be available for use. It may take 20 seconds to cool sufficiently, but I guess at that.

 

What is to prevent UP and DOWN being pressed at the same time? I think what you want are momentary rocker switches

If Up and Down are pressed at the same time, nothing will happen, as both leads of the motor will be connected to ground. This is similar to the situation when both buttons are NOT pressed. Nothing happens as both motor leads are connected to the positive supply.

No need for the momentary rocket switches.

No harm, no foul.

First dry run test of tabs everything looking good. it appears there are no limit switches on the actuators. The motors keep running when actuators are fully retracted and fully deployed

Adding limit switches is easy electrically. If you can mechanically mount switches connected to the tabs where they can remain dry, all it takes are two switches and two properly rated diodes. Each switch is positioned at the limits of the tab, and has a diode placed across the switch NC contacts opposing the direction of current...

Not good at explaining via words. How about a quick sketch?

 

In case it’s not clear, the limit switches are properly rated microswitches

 

When both buttons are pressed BOTH forward and reverse leads are energized. As to limit switches I can't find a PDF for the internals, but this is the normal operating mode for those actuators so I assume limiting is somehow done internally. The sound doesn't stop so the motor is energized, but the actuator is at its end of travel so it doesn't move and no harm is done. The actuator motors could be stalled and depending on an internal thermal overload cutout for protection. All speculation without a PDF. On the ones that I'm familiar with at least. You do hear a change in tone telling you the actuator is at its end of travel or some use a feedback gauge needle or LED bar to indicate position. My boat indicates it on the engines LCD gauge package along with RPM and such. I assume from that relay that this is a fresh water boat? Very nice control buttons plate by the way.

 

When both buttons are pressed BOTH forward and reverse leads are energized. As to limit switches I can't find a PDF for the internals, but this is the normal operating mode for those actuators so I assume limiting is somehow done internally. The sound doesn't stop so the motor is energized, but the actuator is at its end of travel so it doesn't move and no harm is done. The actuator motors could be stalled and depending on an internal thermal overload cutout for protection. All speculation without a PDF. On the ones that I'm familiar with at least. You do hear a change in tone telling you the actuator is at its end of travel or some use a feedback gauge needle or LED bar to indicate position. I assume from that relay that this is a fresh water boat? Very nice control buttons plate by the way.

What schematic are you looking at? The solution provided in post #4 doesn’t behave the way you describe.

 

When both relays are at rest (not energized) the motor leads (in my drawing) are both at ground potential (or negative potential). When either relay is energized - one at a time - positive power is applied to one motor lead at a time, and the motor spins up in that direction - whatever that direction happens to be. IF BOTH buttons are pushed at the same time both relays go active and apply positive power to BOTH MOTOR LEADS. The motor doesn't run because there is no current flow. In essence, the motor leads are shorted across to each other when both relays are active or both at rest. No harm can be done by pressing two buttons at the same time. At best (or worst) the relays being both in the same state will merely act as a dynamic brake.

Now, as far as limits go - we don't have enough information to determine whether there is internal limit switching or some other means of prevention of over extending the motor. Till we KNOW we can only "Speculate". This is why I made the argument for a self resetting fuse. They are readily available and cheap. And in the case of my truck, it got me out of a difficult spot.

In post #1 you said your motors are rated for 20 amps. Here's one of those 20 amp circuit breakers I was talking about (self resetting fuse). (click on the "Here's" above)