CUCV 24 to 12 volt conversion mess

[ranchhopper]

I bought a pretty nice 1008 from a NC municipality a while ago it finally made it here this week. They had converted or tried to convert it to 12 volt and its a mess. I had done a few of the Roscommon conversions over the years but you have to use the P/S alternator and remove the D/S side one. Problem is they removed the P/S alternator and taped off all the wires they are still intact but rolled up and wound up in tape. Can I use the D/S alternator and wire it that way or would it be better to buy another P/S alternator and do it the way I always had before.

 

[Tinstar]

Both Alternators are identical in stock CUCVs.
That way it’s easier on logistics.

But since yours has been messed with, who knows what is still stock or if it’s even same alternator.

 

[ranchhopper]

The one that's on there is the stock unit but I need an isolated ground alternator I will probably find a new P/S one and go ahead with the Roscommon conversion I have done before.

 

[Tinstar]

Both stock alternators on a stock CUCV are isolated Ground.

 

[Bighorn]

The one that's on there is the stock unit but I need an isolated ground alternator I will probably find a new P/S one and go ahead with the Roscommon conversion I have done before.

Which roscommon conversion are you doing?
The batteries parallel single alt 12 volt?
If that is the case, don't you already have everything you need?
Two 12 volt alternators wired parallel is pointless since their voltage regulator can never be tuned precisely the same; only one of them will do the work.


Did they already swap the starter for a 12 volt version?

 

[ranchhopper]

I thought only the driver side is isolated ground since its grounded to the block.

Both stock alternators on a stock CUCV are isolated Ground.

 

[ranchhopper]

Which roscommon conversion are you doing?
The batteries parallel single alt 12 volt?
If that is the case, don't you already have everything you need?
Two 12 volt alternators wired parallel is pointless since their voltage regulator can never be tuned precisely the same; only one of them will do the work.


Did they already swap the starter for a 12 volt version?

They installed a new 96100 starter which is twelve volt I'm going to do the single alternator batteries wired parallel conversion. I have done a few of these and it has worked well but they specifically state the P/S alternator must be used and they are side specific because of the mounting brackets. I would prefer to use the alternator it already has on the D/S but don't know if it works right for the conversion as its not an isolated ground unit.

 

[Bighorn]

Gm made both alternators isolated ground for ease of supply chain replacement.
Any isolated ground alt can be made to function as a standard chassis ground by simply grounding the isolated wire post to the block etc.

Think of it as a ladder.
The first alternator is grounded to the block and supplies power to battery 1 and the isolated ground of the second alternator.
Well alt 2 doesnt know it's ground already has 14 volts potential and it creates its own 14 volts on top and we get 28 volts.
That is the purpose of the isolated ground.
To act as a ladder to make the 14 volt potential of two identical alternators equal 28 volts.
You can swap either alternator in a stock Cucv side to side, it is only where the ground goes for each that makes them special and that is built into the trucks wiring.

 

[Bighorn]

You dont need an isolated ground alt for that conversion then.
If you have an isolated ground alt to use, just ground the post to the engine block.
If it is non isolated ground alt, it will ground itself through the housing.

 

[ranchhopper]

OK that makes things easier then I can rebuild engines but where electric is concerned I'm lost so back to the project.

You dont need an isolated ground alt for that conversion then.
If you have an isolated ground alt to use, just ground the post to the engine block.
If it is non isolated ground alt, it will ground itself through the housing.

 

[ranchhopper]

I removed the D/S alternator to use on the P/S wouldn't fit until I realized the lower bracket was turned upside down. I flipped it over everything is good but need the long through bolt for the lower mount looks like it may be metric the search is on.

 

[Recovry4x4]

The alternator doesn't know which side of the truck it's on. It just doesn't matter. If going to a straight 12V system, iso or non iso alt makes no difference. If it is iso ground, make certain that you ground that stud.

 

[dao]

What is the benefit of using two batteries with the 12-volt conversion? There's added weight, additional replacement cost and there are tons of gas and diesel 12-volt trucks out there that work just great with one battery...as most do. Just curious why not go down to one good battery?

 

[Bighorn]

What is the benefit of using two batteries with the 12-volt conversion? There's added weight, additional replacement cost and there are tons of gas and diesel 12-volt trucks out there that work just great with one battery...as most do. Just curious why not go down to one good battery?

Twice the available cranking amps.
Most diesels have 2 batteries in parallel.

The load of 100 amps for 10 seconds from glow plugs combined with 400 amps to spin the starter will make the reason for 2 batteries quite evident.

 

[ranchhopper]

Exactly that's why most semi tractors have four batteries.

Twice the available cranking amps.
Most diesels have 2 batteries in parallel.

The load of 100 amps for 10 seconds from glow plugs combined with 400 amps to spin the starter will make the reason for 2 batteries quite evident.

 

[ranchhopper]

I got my alternator through bolt today installed the driver side alternator on the passenger side wired up everything following the Roscommon 12 volt conversion and nothing. I have power to the gauges, GP relay but when I turn the key you can hear the starter relay click once but nothing to the starter. I remember this happening to me once before years ago but cant remember which wire wasn't connected to cause this problem.

 

[Bighorn]

I got my alternator through bolt today installed the driver side alternator on the passenger side wired up everything following the Roscommon 12 volt conversion and nothing. I have power to the gauges, GP relay but when I turn the key you can hear the starter relay click once but nothing to the starter. I remember this happening to me once before years ago but cant remember which wire wasn't connected to cause this problem.

Are your battery terminals clean and tight?
When you say one click then nothing, does everything lose power after the click?
If you turn the key to start several times, does it click each time?

I would start by measuring voltage at the small terminal on the starter solenoid itself while the key is being turned to start.
Make sure you have the solenoid under the dash clicking AND in turn the solenoid on the starter is clicking too.
After that It would have to be a problem inside the solenoid or with power to the starter winding via the BIG battery lead.
All your ground wires good between chassis and engine block, Negative terminal block and frame?

Basically, now that you are operating on 12 volts you can just jump the small terminal on the starter solenoid to the BIG terminal on the solenoid and it should engage and spin the starter.
Would have been a bad idea before since the solenoid was 12v and BIG terminal 24 v.
Now it is like any other 12 volt system.

 

[ranchhopper]

Everything clean new cable ends I had the starter off to have it checked I'm sure it there where the problem is only one click at the relay everytime the key is turned no chattering at the starter its self.

Are your battery terminals clean and tight?
When you say one click then nothing, does everything lose power after the click?
If you turn the key to start several times, does it click each time?

I would start by measuring voltage at the small terminal on the starter solenoid itself while the key is being turned to start.
Make sure you have the solenoid under the dash clicking AND in turn the solenoid on the starter is clicking too.
After that It would have to be a problem inside the solenoid or with power to the starter winding via the BIG battery lead.
All your ground wires good between chassis and engine block, Negative terminal block and frame?

Basically, now that you are operating on 12 volts you can just jump the small terminal on the starter solenoid to the BIG terminal on the solenoid and it should engage and spin the starter.
Would have been a bad idea before since the solenoid was 12v and BIG terminal 24 v.
Now it is like any other 12 volt system.

 

[Bighorn]

Everything clean new cable ends I had the starter off to have it checked I'm sure it there where the problem is only one click at the relay everytime the key is turned no chattering at the starter its self.

The relay clicks under the dash but does the solenoid on the starter click?
If you can get a helper, take your volt meter down under the truck and check for voltage at the small terminal on the starter solenoid while the key is turned to the start position.

A set of experiments you can do by yourself to find the problem;
If you don't have a helper, try jumping 12 volts to the small terminal on the starter solenoid;
If you apply 12 volts to that small terminal and the starter Bendix does not engage, so long as the engine block is grounded, your solenoid would be the problem.
If you apply 12 volts to the small terminal and the starter Bendix engages but the starter motor does not, then you know it is the motor itself or connections related.
If you apply 12 volts to the small terminal and the Bendix engages and the starter turns the engine over, then you know the problem resides between the key switch and starter relay under the dash.

 

[ranchhopper]

Got the electrical system figured out today some bad wires were the culprit now onto the next hurdle. Changed out the fuel filter good pressure to the IP and no start not even trying to start so I loosened the lines on the injectors no fuel even after cranking. Going to put the leaky pump I swapped out of the blazer into it to at least be able to move it around here under its own power I know that pump works.