I have an 84 Chevy dually with a 454. It has a factory dual battery set up but it has been hacked and rewired over the years before I got my hands on it. I am having what appears to be a hot start problem but I am not 100% sure. So here are my questions.

Right now the batteries run thru an isolater to connect each other the way I understand it is the second battery will never get a full charge going thru the isolator and is basically a spare battery for accessories. I read that it is better to be running the batteries wired in paralell that way both batteries are getting juice from the alt and keeping them both charged. does that sound right? I am able to jump start the truck by using jumper cables connected to both batteries and no outside vehicle.

And next question is right now the truck has the batteries grounded to the frame. I was also informed that running them to the frame is not the best ground and I should re route the grounds to the engine block itself and that would help what I think is the hot start problem. The truck already has the external solenoid mounted on the firewall.

What do y'all think
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check your other post in troubleshooting...

First, what kind of hot start problem? There are 2 kinds, one is slow cranking, the other is just a click or nothing. Battery should be grounded to the engine block.

First, what kind of hot start problem? There are 2 kinds, one is slow cranking, the other is just a click or nothing. Battery should be grounded to the engine block.

When I go to hit the key there is no response at all the volt gauge goes from 15 to under 8. This truck has had starting issues since I bought it. In the morning it starts fine but sometimes the first hit of the key sounds like the engine is compression locked then it starts after that. I am leaning towards a ground problem

a little off topic but where do you ground a battery that is in the trunk (my chevelle)

to the frame and then run a ground wire to the engine from the frame too.

to the frame and then run a ground wire to the engine from the frame too.

I agree with LeoP.....This should cover you if it is a ground issue

When I go to hit the key there is no response at all the volt gauge goes from 15 to under 8. This truck has had starting issues since I bought it. In the morning it starts fine but sometimes the first hit of the key sounds like the engine is compression locked then it starts after that. I am leaning towards a ground problemCould very well be the ground, you can test it with a meter. Another member gave a good explanation on how, and he put more miles on his Chevelle than anyone else.
Where do you have the negative cable connected? Through the last 34 years of driving the Chevelle, I have found that the WORSE place is the alternator bracket. If ALL of the connecting bolts holding the water pump, alternator bracket, thermostat housing, etc, have been recently removed, cleaned and reinstalled, everything will work normally...for a while. As corrosion sets in and electrical resistance increases, the voltage to the starter via all of these avenues will decrease causing "hot start" problems. I have just had this re-occur with my Chevelle after a couple of years of perfect starts. The simple act of moving the negative cable to the front bolt of the exhaust manifold cured the "no hot start" problem. When connected to the alternator bracket, the electrical ground has to run through bolts which are subject to moisture/corrosion problems. Add the long length of the positive path (along the radiator support, along the left fender, into and then back out of the passenger compartment with #10 wire) and you have a recipe for hot start trouble. If you have hot start trouble, first, connect the negative battery cable to a GOOD CLEAN spot on the engine block. The bolt in front of the fuel pump is good. Use a "star" type lock washer under the bolt head. Make sure your cables are in GOOD condition! The simple act of connecting the negative cable to the engine block will help.

Now, how did I find this? I always carry a VOM in my tool box. I had previously "shaved" off a tiny bit of insulation from the purple wire which runs along the firewall and connects to the "S"
terminal on the solenoid. I had made a short jumper with some #10 wire with an alligator clip on each end. Whenever the problem occurred, I would leave the ignition in the "on" position and clip one end of my jumper to the purple wire (where it begins it's vertical journey to the solenoid). I would then connect the other end for a moment to the positive battery terminal. The solenoid would pull in, the starter would turn, and I'd be on my way. One day, I decided to check the voltage at a couple of points to see where the problem was. I connected the positive lead of the VOM to the purple wire and the negative lead to the negative battery terminal. Even though the solenoid was not pulling in, the VOM read 12.5 volts. Mmmmmmm. Ok. I then moved the negative VOM lead over to the engine block and read 9.5 volts in the "start" position!! The voltage drop was on the negative side, not the positive side. I disconnected the negative battery cable from the alternator bracket, removed an exhaust manifold bolt and connected the cable under that bolt instead. The problem was cured. I first discovered this around 1976. Through the years, if I replaced the water pump and/or the thermostat, I would clean the bolt threads and the bolt holes. I would put the negative cable back (for originality) and everything would be find...for a while! The moral is DON'T OVERLOOK THE NEGATIVE BATTERY CABLE CONNECTION! ;) If all of your wiring is up to snuff, you won't need an external solenoid.

a little off topic but where do you ground a battery that is in the trunk (my chevelle) Personally, I ran a two ground wires, one to the frame and one to the engine block. I also ran a 10g from the engine block to the rad support. Ideally, you want to have as few connections as possible between the starter and battery.

Just an update: today I got under the hood and rewired the charging system and ran the batteries in parallel. moved my grounds to the engine and got rid of the isolator. Both batteriws had close to the same voltage to start off with so I lucked out there. Now with the engoine running both batteries are getting full charge and even after letting it run in the driveway for close to 30 minutes then letting it set for almost ten minutes it starts great. thanks for all the help

and got rid of the isolator.
You may need it because with 2 batterys, they will draw on each other and go dead if the cars sits for length of time. Personally, since you have a charging system, I would use only 1 battery