A solenoid/relay can click like a telegraph operator on steroids and the relay can be complete junk. It's the electrical contact points inside the relay, the ones that carry the current that fail, seldom the magnetics.
INTERMITTENT duty relays have much more power handling capability because their contact size is much larger, but even more importantly the magnetic force that slaps the contacts together is many many times stronger. A lot more amperage. A lot more heat build-up. When engaged too long the solenoid magnetic coil winding overheats then burns out.
I've seen too many shorted 10-MT Delco starters consume 500 amps + from a large chassis battery. This indeed and absolutely will burn the contact points of a constant duty solenoid. Older style big block Ford 460 starters can short and earlier DIESEL 6.9 failed starters taxed their solenoid. Power the solenoid coil and switch from the HOUSE battery not the chassis battery.
Mounted 6" apart, the paralleling wires can be of 6 AWG and they will work fine to jumper. I've done with 20MT Delco Diesel starter rigs and it works fine.
The bonus comes with much longer life for the constant duty solenoid that allows the chassis bank to charge the house bank. 800 amps is a lot of armor.
