SBC reinstallation.

[78K5Blaza]

1978 K5 Blazer, 400 SBC, Holley 4160, 700R4

I rebuilt my 400SBC put in a new 700R4 filled'em both up and its on to the wiring. I completely forgot to take pictures of the grounding locations and vacuum routing for the carb. Is there anyone here with a vac diagram, and/or the engine grounding locations? It has cruise and a/c if that matters....

Thanks in advance.

[Lt.Del]

from my 79....

www.delbridge.net/vacuum.html

you should have a silver label on the radiator support showing the vacuum diagram.

[78K5Blaza]

Nope, been worn off. Thanks for the pictures.

any chance you know where the grounds bolt to the frame/block too?

[Lt.Del]

the rear strap from firewall simply bolts anywhere, i think a common place is the back of the cylinder head where there are bolt holes, like the front of the heads.  

the ground cable from battery bolts to the alternator bracket....










Boy, never know what I find when I go through some of my pics taken in '04 when I removed my 350 from my '79.  I took pics of everything!  I don't know when I had time to do the labor with the camera always in my hand.  
 

[low budget]

Well Sarge, it's guys like you with camera in hand that helps bail out guys like me!

[jbreeves85C10]

I just pulled my 350 and rebuilt. I put the firewall ground strap back on the back of the head where it cam from and where your picture shows. Does it matter that I now have aluminum heads instead of the cast iron ones that were on it? I'm not sure of the conductivity properties of aluminum vs. iron.

[VileZambonie]

Yes and aluminum is a good conductor

[rich weyand]

There should also be a ground strap from the front of the drivers side of the engine (usually the head) to the frame rail by the steering box.

[jbreeves85C10]

Thanks guys..! I'll check the driver side one since I don't think it had one to start with.

[rich weyand]

The issue is that you have four connection points for grounds within the vehicle: 1) the battery negative post; 2) the engine block; 3) the cab and fenders; and 4) the frame rails and box.  The last three all serve as "chassis ground" for some of the electrical items in the truck.  For instance, the instrument panel is all grounded to the cab, the headlights are grounded to the front fender, the tail lights are grounded to the box, the fuel sender is grounded to the frame rail, the engine sensors are grounded to the block, etc. 

These pieces are all electrically isolated due to the insulating engine mounts and the insulating cab bushings -- the truck is basically three electrically-isolated pieces --  so for everything to work, they have to be connected together, and to the battery.  To connect four items, you need three wires.  The block is the hub of it all: the battery, the cab, and one frame rail are all connected to the engine. 

Where you do it isn't important, as long as you do them all, and with heavy enough wire.  The battery connection has to be the heaviest, because, when charging a near-dead battery (like right after you jump start a discharged one), it can pull the full amperage of the alternator.  Similarly when starting the truck, it carries the full starter current.  The other two just have to be able to handle the current of all the cab-connected or frame-connected grounds, and were done at the factory with copper braid, but you can do them with some #12 AWG stranded.  The above are the stock locations, but where you do them doesn't matter as long as you have them.

If you don't have them, weird things happen, like the idiot lights will all glow when the headlights are on, or the fuel gauge will change readings with the turn signal cycling -- electrical gremlins like that.

Oh, and make sure you clean the mating surfaces where the eye terminal contacts the block/firewall/frame rail.  You want clean metal-to-metal contacts.

[jbreeves85C10]

I had posted a specific question regarding my head ground and got the answer. Thanks Guys. What I had not posted was the rest of the information that caused me to look for the head grounding information. Rich, you read my mind and posted exactly every piece of information that I need..! :-) Here is the history and reasoning behind my research. I floated a valve and decided to do my first full rebuild so I pulled the engine. Due to my OCD I guess, I basically traced and figured out where all of the wires in the engine compartment were going, what they were for, and why some were missing or cut off. I then rewired the entire truck. This helped to me to learn how everything worked together under the hood and throughout the vehicle. I did this with the vacuum and ignition system as well and ended up installing the MSD 6AL with MSD Dist. I felt like I took enough pictures and did enough reading and had everything tip top but saw a few of these gremlins like you mentioned. With the AC/Heat off and the temp slider half way between cold and hot, I was sitting at a stop light for a good bit. When I took off, billowing smoke came out of all of my vents in the cab. Of course, being my first rebuild, I about shart myself thinking I had caught the truck on fire :-) This happened a couple of more times so I asked my cousin about it. He immediately said to check all grounding. The AC and heat work fine BTW. I got my trusty continuity meter out the other day and checked grounding to the rails, heads, block, firewall, front clip, etc and all seemed good but I was still in a bit of doubt so the information you posted will be awesome for me in order to really check everything knowing that I have good solid facts to check out. The other weird gremlin I saw about the same time is that I now have engine noise in my stereo system. I have battled with this many times in the past and know that I have a solid connectivity and grounding scenario within the system. I'm running 2 subs with two 1,000 watt amps, one bridged on each sub, and then a 3rd amp for mids and highs. Nothing elaborate but throwing the amps into the mix always most certainly results in engine noise if you don't wire the system correctly in regards to grounding and which wires not to run in proximity with others...cross talk etc. One last gremlin that was pointing me to grounding issues was a specific switch I have installed in the cab. I have a little Autozone 4-way switch that is a pretty basic setup. It has an adhesive push button touch switch that is stuck to the bottom of my dash out of site but I can easily reach. Under the dash is the switching mechanism which grounds to the cab and then powers each pole. One pole has my rear view mirror LCD and backup camera and the other 3 poles have LED lighting for the cab and under the hood. Randomly, one of these circuits will just come on and stay on as if the battery were disconnected and reconnected (lost ground) so I was thinking I might have a bad switch. Now that I am reading your grounding information here and thinking more about everything involved, I think this may all be the same issue. Thanks a ton Rich for your reply..!

[rich weyand]

De nada.