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  #1  
Old July 16th, 2020, 06:56 AM
Deer-Slayer_5 Deer-Slayer_5 is offline
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Default 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!
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Old July 16th, 2020, 09:38 AM
graflex graflex is offline
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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
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Old July 16th, 2020, 10:05 AM
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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.
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Old July 16th, 2020, 11:31 AM
Deer-Slayer_5 Deer-Slayer_5 is offline
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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?
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Old July 16th, 2020, 04:57 PM
graflex graflex is offline
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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).
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Old July 18th, 2020, 03:50 PM
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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...
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Old July 18th, 2020, 06:03 PM
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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).
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Old July 24th, 2020, 05:40 AM
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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!
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Old July 24th, 2020, 09:34 PM
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Hopefully we are helping...keep the updates coming!
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Old July 30th, 2020, 05:28 AM
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Quote:
Originally Posted by brute4c View Post
Hopefully we are helping...keep the updates coming!
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.
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