I have read on this forum that there should be 3 grounds; battery to engine, engine to firewall and engine to frame. Is this correct? I have the battery to engine strap and I just ordered the engine to firewall strap. I haven't seen anything specifically for engine to frame. I want to make sure I have the correct set up for the 6V positive ground system. Does anyone have a picture of their set up?

 

I don't have a pic sorry, but that sounds correct.
Keep in mind that grounds are kind of like money and ammo, there's no such thing as to much lol.
Also,
On my 1958 ford 641 workmaster, it was orig a 6v positive ground, I actually switched it to the typical - ground.

 

I don't think Ford had an engine to frame ground. It can't hurt, but if everything is already in good shape it won't help either.

 

Isn't it already grounded? It is bolted to the frame after all...

 

Good grounds don't care what side they come from or what voltage and there is no such thing as too big or too many.

 

No point in running a ground from the Engine to the Frame as all is mounted on rubber. Battery ground strap to Cowl, then Solenoid to Starter. But more ground straps don't, but the main ground strap the important one is Battery to Cowl.

 

While I agree the motor mounts/bolts ground the block-frame, I've also seen several instances where after time-rust, oil, mud, etc can cause that ground to deteriorate over time.
I look at it like insurance,
Having a ground cable from the block-frame isn't going to hurt a dang thing, it's a "just-in-case" ground.
To each their own...

 

Actually the rubber motor mounts are a pretty good electrical insulator. There is not metal to metal contact when they are new. The engine to firewall and battery to firewall are sufficient though, if they are in good condition.

 

My 41 and 47 COE trucks both have a braided ground strap from the rear of the engine to the frame.

After the engine rebuild for my 47 it would barely crank over. Had to sand off some paint where the braided ground strap was fastened to the newly painted engine before it would crank as usual. So that ground strap is definitely needed.

Still using 6 volt positive ground.

 

Good grounding is essential, it was marginal when they were new, 60 years of corrosion and rust doesn't help. It's amazing the problems that result. When ground straps are loose, corroded or missing the current will take whatever alternate path it can, through components that don't normally see see it. Starters draw hundreds of amps and will roast things far away or inside gearboxes, u-joints, throttle cables, wheel bearings, radiators, fuel lines.. Not Good. Restored trucks may not have any rust or corrosion, but likely have thick coats of primer and paint and can cause similar problems.

 

Remember that you need to use much heavier gauge wire on a 6 volt system than is needed for 12 volts.