@rampage, between the two of us, if we could get enough sleep, there would be no stopping us....
I could not find any spec sheets on that relay either. But somewhere, Amazon I think, I saw a complaint in the comments section about the fact that it tied both outputs to the negative terminal when there was no control input. And a couple of other folks said the same thing.
So, you do get braking with it.
What I don't understand, is the duty cycle.
It changes with the current load. Which I take to mean that the contacts and the internal wiring to those contacts will heat up under those loads. If so, then I assume that there is an upper limit where the heating is not a problem. And if you get 5 minutes without damage at 70 amps, 35 is probably going to be approaching that limit. I suspect that its going to be better than double.
But, what about the internal actuating coils?
The link
@diesel4me posted gives the duty cycle as continuous. I'm guessing that means the coils.
What I am unclear about is fairly basic. Didn't the original system have two motors? And if so, did they both run off the one relay board?
The friend's setup seems to add an unnecessary switch to the mix. It just happens I have used several of the rocker type switches to control and reverse fairly heavy current DC motors. I never found one that was rated more than about 20 amps. I switched more than that, but always had a spare handy.
HANG ON A MINUTE!!
You folks really should not treat a poor brain scrambled turkey hunter this way.......
I was beginning to think I was in worse shape than I thought.
Could not figure out why the heck we were introducing a DPDT rocker switch wired in reversing configuration into a system that was working fine without it.
Then the whole 6V vs 12V vs 18v, really scrambled me up.
Then when
@pblaze725 said the reversing switch came with the truck, something finally snapped. I knew darn good and well that there was no reversing switch in the system I had been working with.
Looking back through the posts I finally found where there are two different posters. Now it makes sense.
So, here goes.
@centexk5, keep looking for a resistor. You may have to replace the relays with either heavier ones due to the current draw, in which case you can get the 12 volt ones and forget about the resistor.
If you do decide to replace them, the one reversing relay suggested before might be a good choice. It would be a lot heavier and would replace both relays at the same time.
@pblaze725, that relay would probably do the trick, but you need to replace the rocker switch with a SPDT switch with center off and maintained in all positions. That would control that relay well.
As for using both 12 and 18 volts, it should work if you are careful. The negative terminals of both the 12 and 18 volt batteries will have to share the negative post of the relay since the internal coils are hooked to it.
Make darn sure that the positive terminals of the two systems never touch. Bad things will result.
For both of you, if you want, you might consider drilling the rivets out of the relay when you get it and inspecting the internal parts. There were several posts on Amazon about them having very poor quality control. Supposedly they tended to work once or twice and quit, or only work in one direction.
A couple of folks opened them up and found that the design was OK, but the parts were not installed properly and the moving parts hit each other and could not function. In one case, part of the contact mount had been bent to make it work and the contact was not touching correctly and burned up.
My guess is that several companies make them, and some do better than others.
If you don't want to risk it, two regular 12volt DPDT relays wired like the board of
@centexk5's system would drive both motors if they were heavy enough. And only need the SPDT switch I mentioned before.
And yes, they could be triggered with 12v and control whatever voltage you wanted to use to drive with.
I am going to take a nap, then get up and drive into town in defiance of the lockdown order.
Get some diesel for my tractor and spend the rest of the day trying to get my fields ready so I can try to get some kind of crop in the ground before it gets too late. I will check back in tonight.
I need to let it all soak in and re-read it more thoroughly. But if this was my project I’d do what 
