Any CUCV 24v to 12v Conversions Here?? M1031

[TigerTodd]

My 1986 M1031 was converted to 12v by an imbecile, box scrapped and I'm having some electrical starting issues, you can see the link below.

https://www.steelsoldiers.com/threads/melted-6-fusible-link-won’t-start.214514/

I'm wondering what I've missed? This #16 fusible link melting then somehow turning into a wire that will turn the starter over and start the truck when you reconnect it, is baffling to say the least.

Has anyone done the 12 V conversion differently than the rosecommon method?

Any and all info is greatly appreciated thank you.

 

[Rickf]

What starting (or lack of) issues are you having? For a full 12 volt setup the starter and glow plugs need to be changed. Is the massive resister (not needed) still on the firewall? On my old cucv blazer I used a 555 timer and ford type starter solenoid for the glow plugs, they draw a lotto amps.

 

[Buck69]

Do you still have two batteries in parallel then or are you down to 1?
Haven't done the 24 to 12 conversion yet, but will be doing so soon.
Truck is currently stripped to the frame, but have pics, notes and the OE harnesses on hand.
Am doing the diesel to gas conversion as well.
Here's a pic of an unmolested M1008 harness if it helps.

You must be registered for see images attach

To add, this truck has 3 relays hidden in the dash on a bracket below the ash tray. Are yours still wired into the cab harness? They are for the 24V system. The big one is the start relay and the smaller 2 are for gen 2 and the Volt gauge.

 

[TigerTodd]

wow this is the most reply's i've gotten anywhere, so thx guys!
I'm wondering if that 24v start relay has something to do with it. does that need to be changed to a 12v starter relay?
The truck was converted using the rosecommon method, batteries are wired parallel.
Also pls see the steel soldiers link I posted giving details.
I'm going to shoot a video showing the rig.

 

[Corvette Ed]

Yes,your 24v starter relay will need to be changed to a 12v relay

 

[Buck69]

I did read the link you posted. You indicated that additional momentary switches were added for 12V start and glow plugs.
Have you gone through the parts and electrical diagrams in the TM's they have?
That is where I found and identified the 24V relays. I have not opened up my harnesses or actually even spent much time focusing on the electrical yet. Just enough to understand what I was disconnecting during teardown. (Body is removed and getting bed liner applied to full underside)
Try pulling those relays if they are still in there for diagnostics. Sounds like they aren't being used at the moment.
There are several on here that have done this conversion. Hopefully they will chime in.

 

[TigerTodd]

i have gone through the TM's and I really couldn't find an answer. I really hope they chime in... i haven't talked to one anywhere yet.

 

[Blue Ox]

Were the injection pump solenoids changed to 12V?

 

[Buck69]

It is pretty tough to guess what the previous owner has done. The top bus bar was 24V+ as a CUCV. The fusible link you are referring to, may have came from the second generator for charging the 24V system. Where does it go now?
As mentioned, I am a bit away from doing this conversion so take what I say with a grain of salt.
It is my understanding that the relays are all switched with 12V meaning they are 12V relays. The controlled side of those relays (or larger posts) carry 24V. I am betting the glow plugs may even be the same as well and is why they had to install the big resistors on the firewall. It would allow both batteries to be utilized for the start and glow plug circuits as well as allow boosting from other equipment if ever required.
I will take a look at at my harnesses and relays tomorrow to see if that is correct.
It sounds like the previous owner has incorrectly dealt with the 24V feeds in the cab harness and possibly burnt some stuff up.
Load up some pics with decent field of view of their handy work.
It will help us help you.

 

[khamill2000]

ALL - The only 24V CUCV part is the starter. All others are 12V. Glow plugs, IP, relays, etc. All are 12V.

OP - The Roscommon method works very well. Also check out the Doghead relay mod. There is a starter relay under the dash that goes bad on almost all of them.

doghead starter relay modifcation

*** WARNING LABEL *** Disconnect both batteries before attempting this procedure ____________________________ Credit goes to doghead for his instructions in thread "underdash starter relay" and the wiring picture as well. This modification replaces the standard GM underdash starter relay, GM...

www.steelsoldiers.com

 

[Strick]

To add, this truck has 3 relays hidden in the dash on a bracket below the ash tray.

I used a CUCV wiring harness when I first built my 55 Chevy. The CUCV have those 3 headlamp switches for blackout and have the relay strip under the dash that the purple wire for the starter runs to. I bypassed all that jazz and didn't have any issues. I cannot remember on the firewall strips how it was that I used just one alternator and 12v parallel dual batteries; but it is possible. All those other battery cables going to the "slave" port in the grille and many others off the strip can be tossed when doing the 12v conversion. Just remember to use a 12v starter in place of the 24v.

Strickland

 

[Frankenchevy]

The CUCV have those 3 headlamp switches for blackout and have the relay strip under the dash that the purple wire for the starter runs to. I bypassed all that jazz and didn't have any issues.

…but the black out switches are one of the best things about a cucv.

 

[Strick]

…but the black out switches are one of the best things about a cucv.

NOT a thang works when they're flipped tho. Covert operation.

Strickland

 

[Frankenchevy]

NOT a thang works when they're flipped tho. Covert operation.

Strickland

I know, it’s nice creeping along without lights giving up your position. I’ve only used them a couple times in all reality.