402 big block solenoid wiring

[Bigblock50]

I’m installing a new starter/solenoid on my 1972 GMC Sierra Grande with a 402. Starter is in and the “S” wire is attached. Problem is how to route the big plus cable. The solenoid in crammed into a compartment made by the starter below it and by the block and dual exhaust header above. Access and visibility are poor. My first attempt resulted in hidden contact between the big plus cable and the S wire, generating a loud “snap” when I momentarily tapped the ground cable to the battery terminal. So I took off the plus cable pending advice. Would it help to use a right angle terminal on the plus cable?

Bill in Luray

[RustyPile]

Route the Positive cable straight down from the battery to the frame.. Run it along the frame for about 3 - 4 inches and then turn it toward the block just behind the fuel pump. run the cable along the pan/block juncture and below the motor mount.. At this point the cable will be slightly below the battery cable terminal on the solenoid.. Make a 90 degree turn in the cable with the cable terminal pointed slightly upward. Attach the cable to the solenoid... Once the cable clears the frame, make the run without any slack.... Attach the cable to the frame and block using those insulated wrap around clamps.. Bring the purple "S" wire (and the yellow wire if you don't have an HEI ignition system) down behind the Passenger side head and connect to the starter.. Route the wire through one of those insulated clamps attached to a lower bellhousing bolt.. It's crowded under there but there is room to work...

[Bigblock50]

Rusty - very detailed, I’m much obliged! I’ll pursue it tomorrow. I have HEI so no yellow wire.

[CABLESCUM]

Same thing here except I have Hooker 2455 Chevelle Hookers on it...tight spot. Thinking about one of the small high torque starters(Solenoid probably still oriented the same). My batteries are in back by the compressors so I snuck it along the frame, but it’s still close enough to heat up the +.

Good luck

[Bigblock50]

Right. I thought about the smaller starter but it’s the darned solenoid! I actually wired it up on the floor thinking that would make the job easier. But struggling to get it installed between the cooler lines and the frame, I managed to force the plus cable out of position. It would certainly be easier with a six foot lift and lots of bright lights.

[RustyPile]

Originally Posted by Bigblock50

Right. I thought about the smaller starter but it’s the darned solenoid! I actually wired it up on the floor thinking that would make the job easier. But struggling to get it installed between the cooler lines and the frame, I managed to force the plus cable out of position. It would certainly be easier with a six foot lift and lots of bright lights.

Jack up your truck high enough to comfortably work under it from a creeper.. (You do have one of those, don't you?? ) If you can't disconnect the wires and cables with the starter bolted in place, remove the mounting bolts but don't remove the starter. Instead, build or otherwise obtain a large box and position it on the floor directly under the starter and set a jack stand on it.. Slide the starter forward toward the radiator enough to gain access to the connection points on the solenoid.. Raise the jack stand enough to support the starter. It's almost impossible for the starter to fall because of the exhaust, frame, and transmission cooler lines..

Having been an automobile mechanic for over 30 years my hands grew eyes.. I can feel my way around places my eyes and drop light can't reach.. I've never weighed more than 170 lbs in my life.. I have small hands and long fingers that can work in small places.. I use 1/4" drive sockets, extensions, and other compact tools when working in tight places.. In places where I can't swing a ratchet, I have a small battery powered 1/4" drive ratchet.. It will tighten 6-32 fasteners without striping the threads.. I also have a 1/4" driver handle that accepts sockets and extensions..

[Steeveedee]

Originally Posted by RustyPile

Jack up your truck high enough to comfortably work under it from a creeper.. (You do have one of those, don't you?? ) If you can't disconnect the wires and cables with the starter bolted in place, remove the mounting bolts but don't remove the starter. Instead, build or otherwise obtain a large box and position it on the floor directly under the starter and set a jack stand on it.. Slide the starter forward toward the radiator enough to gain access to the connection points on the solenoid.. Raise the jack stand enough to support the starter. It's almost impossible for the starter to fall because of the exhaust, frame, and transmission cooler lines..

Having been an automobile mechanic for over 30 years my hands grew eyes.. I can feel my way around places my eyes and drop light can't reach.. I've never weighed more than 170 lbs in my life.. I have small hands and long fingers that can work in small places.. I use 1/4" drive sockets, extensions, and other compact tools when working in tight places.. In places where I can't swing a ratchet, I have a small battery powered 1/4" drive ratchet.. It will tighten 6-32 fasteners without striping the threads.. I also have a 1/4" driver handle that accepts sockets and extensions..

Boy, do I know about "eyes in your hands"! Sometimes when I'm in a bad spot, I actually close my eyes and let my fingers do the walking. Now, if I could be that 170 pounds again...

[Bigblock50]

Yeah, it's up on ramps and the Bone creeper is pretty comfortable. I agree with the usefulness of 1/4" sockets. (I also work on farm tractors where they come in handy too.) I got the starter bolts in today using a lithium ion right angle 1/4" socket driver, great little tool. I thought I was home free then but this has been a long haul with this truck's wiring.

The basic design is bad - the solenoid base should have been positioned in plain sight. Some of the fancy aluminum billet starters have the "solenoid" connections on the bottom - what a great idea! But they require shims to get the flywheel engagement right. No thanks.

[kwmech]

There is also the Ford solenoid install also to help simplify the wiring at the starter

[weq92f]

.
The mini starter does make it a bit easier. My positive cable runs along the oil pan.

Hth,

-klb

[Orange Crate]

This starter might change the cable routing and might make things easier in the future. I grabbed this image from Dirty Larrys build.

[Bigblock50]

Well, I got the plus cable installed as suggested by RustyPile. In doing so I noticed the factory loop-clamps that are invisible looking from the top. (Note-this truck has AC meaning lots of junk on the battery side of the engine compartment.) No shorts like before when I grounded the battery but the vehicle was once again dead. Cause was that the short blew the fusible link again. I can get another one tomorrow at AutoZone.

For the information of those who haven't followed this whole saga ... a few weeks ago the fusible link on my 72 GMC blew suddenly, leaving me stranded, thankfully close to home. The short came from a "birds nest" of wiring and electrical tape near the battery, an attempt from many years back by a PO or gas station to wire the truck for a camper. I decided that the birds nest had to go and didn't expect a problem as I don't have a camper.

Wrong. After deleting lots of extraneous junk the electrical system was fine but the truck would not crank over. Lots of wire tracing followed until I discovered, with forum help, that underneath a bunch of electrical tape near the firewall junction block, the evildoer had spliced into the purple wire leading from the neutral safety switch to the solenoid (SEE PICTURE) and rerouted it into the birds nest as a BLUE wire. Why would anyone do that?? I don't know. Unsafe for sure. Anyway, I've rewired the purple wire directly to the solenoid. In the course of fixing all this, I found numerous cases of splices under tape, always with a color change, purple to blue, green to black, etc. Some splices were just twisted wires! I have just a few more "unknown" wires to check out and probably delete, once I get the truck started again. What a pain--but in the end the truck will be a much safer vehicle to drive.

Bill in Luray

[RustyPile]

Small rolls of proper color and gauge wire is available from most well stocked auto parts stores.. When you make those repairs, don't use tape as an insulator, nor use butt connectors to make the splice.. Twist and solder the joints and use heat shrink (multi layers if possible) to cover the bare wire...