12v electrical help for those who have a SBC

Hey guys, this is my first post and I'm pretty new to the forum. I have been a lurker on here and now I am needing some assistance.

My dad and I have a 1968 M715 that is being restored. Currently, we are wiring up the engine which is a 305 SBC Novak swap that came with the truck from the previous owner. There is a tuned port injection system on the engine that I picked up from another SBC. We have everything for that system which is no problem.

The truck is going to be 12 volt now and I think I can see some issues coming about. Can anyone point me the direction of switching to 12v the correct way? We would like to utilize the factory wiring harness to the lights but I know there can be some issues with this. Would it be better to drop the factory harness and combine everything into one fuse block, or can this be done with the factory harness? We want to be able to run all blackout lights.

I used the search feature for swapping to 12v but couldn't find what I was looking for, so excuse my ignorance. If anyone could attach links to other forums or threads or simply give advice on how to do the electrical properly, my dad and I would much appreciate it!

Thanks!

I switched mine to 12V. Mostly changed bulbs (see the Wagner bulb list in the manuals section). I used a 12 to 24v converter for the gas gauge (about $30 on ebay) I didn't want to drop the gas tank. Headlights are 12v halogens, you need new connectors. I also replaced the battery gauge with a new 12v unit. Bulbs are cheap on ebay compared to auto parts stores. I have an EZ wiring kit, but presently using the original harness. My directionals work on 12v. My M725 is also a 1968 and has the Chevy 350 with the Novac kit. Easy Job

As stated above. Switching to 12 volts is mostly just a matter of changing out bulbs and a few other small things. All easy.

The big question is which blinker system do you have on your truck. Look at the firewall between the brake master cylinder and the hood hinge. Is there a small black finned box there with a 3 pin connector or a huge centipede looking multi wired box? If you have the small 3 pin box, it will work just fine on 12 volts. The big Spartan box will not. You can switch over to the solid state controller though.

So far, thank you guys for the advice! @Barrman, we have the big spartan box and I saw on here the solid state conversion. I added that conversion to my list of things to do. I'd like to keep it original honestly even though you wont see it unless the hood is open.

If we can get the EFI to run as a stand alone, I think lights and gauges should be a breez, We are getting 12v gauges of course as well. The electrical harness we have seems to be in great shape. It came with a rot free cab we picked up in northern TN so hopefully we don't have to run new wires then.

Are there any fuses/ fuse blocks that need to be in place for the lights? The EFI should have its own but what about all other wiring?

I still use the 3 lever switch for lights. you may have to get a small fuse block for other loads (I have one for radios and heater).

Both styles of turn signals came on these trucks so the only way to tell would be to know that none of the early trucks were of the solid state, non Sparton type and approx. what vin the solid state started at...when the solid state started, there are still trucks mixed in with the Sparton setup...basically, if they ran out of a component to install the solid state, the went back to the Sparton setup until they had the solid state parts again...

Jeep did it cheap...

I ended up ripping the stock harness out of mine and completely re-wiring. Used a Painless fuse block and rolls of wire and lots of tape and wire loom. When I started testing and metering the original harness, I'd put 12v on one wire, and read 12v on 3 or 4 others that shouldn't have been hot.

Mine was missing the signal box, just had the lever on the column. I just took the 3 (?) leads from the turn signal switch and wired them direct....and used a couple of diodes (think of them as one-way valves for electricity) to keep from backfeeding thru brake light circuit (both sides connected there).

Just to provide an update for those who have been following. We have been wiring up the engine first, that's going pretty well just slow due to the hot and humid conditions lately. I'm hoping here in a week or so we can get the engine running and then we will figure out our approach to the rest of the truck.

a huge thanks to all the input so far!

Hopefully we are helping...keep the updates coming!

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Originally Posted by brute4c

Hopefully we are helping...keep the updates coming!

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Yes, you guys are helping! I saw this as a more complex job than it really is...

But to provide a further update, our truck had the spartan box but we didn't have the original wiring harness for that truck. So we got a wire harness that was from a truck that apparently had the solid state flasher box. Not knowing that 10 months ago, we thought we were in good shape. After talking to you guys, we realized we had the solid state flasher unit wiring harness.

Is there a way we can convert the solid state wiring harness back to the spartan box or is this more work than what its worth? The only reason I say this is because we like the Spartan turn signal lever since it is original to the truck but if it is not functional with the newer style wiring harness I'll forget about it.

I made a page where I converted from the Spartan style to the solid state style...it didnt require removing any wires but a few were not used anymore...that page would give you what wires were changed and what went where originally.

I also took the whole wire harness apart and documented where each wire originated and where it went. With that you should be able to figure out where the wires that are no longer on the solid state harness originally where and thereby reintroduce them to the system in order to have the original style turn signal harness.

We also have the complete wiring diagram, made and given to us by a very generous member RBoltz, that is better than anything Jeep every did and covers the early turn signal setup AND another that covers the late style.

Turn signal conversion page is here:
http://www.m715zone.com/vb/view.php?...signal_convert


Wire harness detail is here:
http://www.m715zone.com/vb/view.php?pg=early_harness


Wiring Diagram for early style turn signals:
http://www.m715zone.com/vb/pages/man...ck_distbox.pdf


Wiring diagram for late style turn signals:
http://www.m715zone.com/vb/pages/man...solidstate.pdf


Besides the specific wires from the Spartan turn signal switch to the distribution box, there are only a couple wires you need to do anything with...start with the turn signal convert page...I documented the few wires that had any changes at all...those and the ones from the turn signal switch to dist box are all you need to play with...

Shouldnt be too hard really...I hope...

Try this link: http://www.m715zone.com/vb/pages/man...st_convert.pdf

brute4c, Thanks for those links! I have everything I need to do the spartan box guts exchange and that doesn't look to difficult. The harness we have has good readable numbers so I cant see it being a wild goose chase on finding what wire is what.

I'll report all this to my dad and see what he thinks. It's ultimately his truck, I'm just helping him get it together and learning old vehicle tech. Working on this truck is wayyyy different than my CJ-7 project I have going on as well. Either way, I'm learning new stuff!

I went to a 12 volt system and replaced all bulbs with the new LEDs that have come out. Got the head lights in the LED mode also. If u ever want to go back to the 24 volt system , the bulbs are rated for 24 volt range.

I know its been awhile since the last update. It turns out we have all the right components except for the turn signal lever. My dad is going to order that and move on. He likes the older look but we will keep the old stuff just to keep around.

As far as the engine wiring, we are moving along with it. It has been hot and humid and that makes wiring more frustrating in my opinion. The information you all have given me has been great!