So I have this 83 MQ Patrol as some of you know. The p/o had the trucks glow plugs running on 12v. He also unhooked the auto-glow system in the truck. So he put in 12v glow plugs in a 24v system by wiring a hot wire off one battery to a solenoid or relay and then to the 12v glow plugs plus a wire to the push button. The Patrol for a long time was in Southern Cali so I assume this was enough to start the truck. I also am thinking he did this because the 12v glow plugs are a lot cheaper than 24v ones and easier to fine.

Well I live in Wyoming and it gets cold here. The 12v set up has been working for me all summer although the truck can be a little hard to start at times.

Anyways I went and bought some 24v glow plugs. I put them in the other day but didn't change out the 12v solenoid. So the truck was actually harder to start since I was trying to power 24v plugs with only 12v, ie the 24v plugs not getting hot enough. So today I go pick up a 24v solenoid which is exactly the same as the 12v in terms of shape, size and # of posts/terminals. I wire it up the same way the 12v stuff was wired up. But I think I am still only supplying 12v to a 24v solenoid/glow plugs. The result is still cold glow plugs. I started the truck after doing this but it didn't start very easy.

Now after all that blahing here is what I need help with....

How do I put 24v into the solenoid and thus to my new 24v glow plugs? I tried running one wire from each battery to the hot side of the solenoid. But this causes the second wire to get very hot, start smoking and if not removed I am sure it will melt or start a fire. FYI I currently have 1 wire to the solenoid from one positive side of one batery. When I ran a second wire it was from the positive on the other battery, ie I had 2 wires both from positive terminals on each battery.

So how do I do this to safely supply 24v to the solenoid/glow plugs?

To get 24 volts, you need to connect the positive from one battery to the negative on the other battery. Once that is done, you will get 24 volts off of the second battery.

The thing you have to be careful of is that your 12v systems only come off of one battery.
By bringing positives off of two batteries, you were getting 12 volts at twice the current capacity.

The wires were getting hot because the two batteries were trying to balance the power between them. The stronger one was directly charging the weaker one.

the batteries need to be wired in series
to achieve 24 volts.

"series" just means positive to negative:
example: (4) 1.5 volt D cell in a flashlight will power a bulb sesigned for 6 volts.

Measure the voltage from the positive on the first battery, to negative on the second battery.

When you have the meter hooked up right(find 24 volts) you'll be closer to solving your wiring issue.

Ya I understand how 24v works. The truck is stock and I have 2 red top optimas wired in series.

I guess what is confusing me is that the 12v stuff was wired off battery #2 to the positive terminal. That is where I should have 24v right? If that is the case then it seems odd to me the 12v & 24v stuff will be wired the same.

It was getting dark last night. I will check more this morning with my volt meter.

Well it turns out I am getting 24v to the glow plugs and also to the relay. Unless my pos cheap gauge is wrong or I am to stupid to read it I think I am actually getting 30v to the relay/glow plugs. The gauge is telling me 30v in the relay, 30v out and 30v at each plug. This being wired up exactly the same as how it was wired with 12v stuff.

Now I bought a 24v relay from Napa, the expensive one that is internally regualted. This relay is giving me probs. It only seems to work when the truck is cold and I haven't started it yet. It works for the first glow but after that no power through it. Perhaps it got damaged when I was farking around with the wires? I am not sure but couldn't start the truck with it. So I put back the 12v relay which is working fine and allows me to start the truck. The 12v relay has the same power in and out and to the glow plugs. It works every time I push the button. Now I would be worried but this 12v relay has had the same power through it since beofre I bought the truck and there is no problems. When I get a chance I am returning the 24v relay to Napa and see if I can't get a new one.

Seems a little odd a 12v relay is taking 30v and is still working just fine. This is also the root of my confusion here...