Wiring Harness

[49 Caddy]

  In the process of converting my 49 Caddy to 12 volt and new wiring harness.  Got the dash pulled out, which should make it a little easier to get to stuff.  Any words of wisdom from anybody out there that has experience doing this?  My wiring is shot, but it is mostly all there.  It is a universal 22 circuit harness, more than what I should need.  Series 61.  I should mention, the interior is removed and there is no engine or tranny as well.  All, either re-built or in process. Just not quite sure where to start.

[fishnjim]

Start at the battery and work out to the fuse block, then the branch circuits.
Some of those gauges/lights will have to be replaced/modified for 12VDC unless you've replaced all.
The alternate is to one by one replace each circuit/wire but it's more difficult to wrap/sheath the main branches.
I don't know that you gain much with the dash out, other than "room" for access and not work in tight space.  They still have to fit/be right length with it in.  One could wire the dash off and then make a multipoint connection disconnect.  Sometimes there's connectors on the dash like that anyway.  Probably did not come with your set or enough wire for some that route.
It may help to put the harness on a plywood(4x8') and collect wires that go to the same locale for routing and make sure they're labeled correctly.  That's how they make them up to get the right length.  You should follow the 6 VDC electrical diagram for routing so it fits correctly.
Some of these "kits" come with install instructions, so you may want to read or contact your supplier.

[Dave Ventresca]

I installed a new wiring harness in a 49 conv. good luck installing the heater. its a tight fit. Dave

[wheikkila]

I have converted many of 6 volt systems to 12 volt. Couple things, you will need to change the cigar lighter and dimmer switch. One more thing I did. I added a small 6 volt fuss box for the things I didn't convert to 12 volts like Radio, heater.   
                   Thanks Wayne     

[Chopper1942]

Is this like a Painless Harness.  If so, all your wires a color coded and numbered for each circuit. Just follow the installation book.  It will cover most of what you need.  Also, get an OEM 49 Caddy wiring diagram, colored preferred, and use it to reference your circuits.  All of the bulbs will need changed.  The generator and voltage regulator, or better yet replaced with a 10SI alternator, 12V ignition coil with a resistor, and horns.  The 6V starter will work OK.  It just spins the engine faster, just don't crank for extended periods of time. I used a 6V starter on a high compression "souped up" Olds engine in my 37 Ford 60 without any problems.  If you can find a 12V starter, install it.

I am rewiring a '40 75 limo.  I started at the battery.  Install as large of battery cables as you can.  2 guage has more strands than 4 guage.  Run the B+ cable to the starter or junction/maxi fuse block. If using a junction/maxi fuse block to the starter.  B- cable from battery to engine block. Clean paint off block, use a star washer between cable and block.  Attach 2 flexible woven battery cables between the engine block and the first to the body and the second to the frame. This ensures that you have good ground paths for everything on the vehicle.  Divide your 21 circuit harness wires into separate looms.  Engine, left front, rt front, instrument and dash wiring, and the rear harness. Wire each circuit 1 at a time.  If the proper connectors are not provided, use heat shrink butt connectors to splice onto the OEM connectors. I would start at the dash and do the ignition switch, headlight switch, and dimmer switch.  The OE switches will work OK. They are designed to carry more amperage than 12V switches. Once they are wired, wire the front headlights and park lights.  Now use a jumper wire, with a 15 amp fuse installed, to connect the battery B+ to the B+ feed of the headlight switch. Check if the lights work correctly. If OK, now do the rear tail, brake, and license plate lights. If everything works OK, continue on. Otherwise, trouble shoot the circuit that doesn't work.
Now do the rest of the dash and accessories. The instrument gauges should work OK except for the gas gauge. It will need the B+ to be 6V to read correctly. The oil pressure and coolant should be mechanical and the ammeter just reads the amount of current that passes through it. The clock, if electric, will need 6V or reworked to 12V. The same applies to the radio. I would run all the 6V accessories that are not replace off voltage reducers for each application, 1 for the radio, another for the clock and gauges, and a separate one for the tube radio. The reducers must be mounted on a metal surface with good air flow around them. I would install a separate small fuse block with 12V power and install the appropiate fuse for each reducer. Run the wire to the reducer and then to the 6V device.  This will allow you to use and retain your OE accessories.  The radio can also be upgraded to modern guts if it doesn't work.

The engine wirng can be done at any time, but I usually do it last.  It is usually straight forward unless you change to an alternator.  If you use a 1 wire alternator, you won't need to install an exciter light for the internal regulator.  Make sure you install a ballast resistor for the coil.  Run a wire from the starter solenoid post that has the wire from the ignition switch to the distributor side of the ballast resistor.  This provides 12V to the coil when cranking for a hotter spark.  If you do not install a ballast resistor, you will burn up the points and coil.

I am sure I missed some things, but if you have questions, I will follow the thread and try to answer them.  this is a big project and will take some time. Just don't get discouraged. If you don't understand something, just ask.  I or others are glad to help.  Hope this helps.  Good Luck!

[49 Caddy]

  Thank-you, so much for the info.  I should have my new firewall grommet in the next day or so.  Want to install that before I start running wires.  Believe me, I will be asking more questions.  Thanks again.

[Chopper1942]

I just spent an hour explaining some other things and when I hit post it didn't post.  Don't cut any hole in your firewall until I have time to respond.

[Chopper1942]

What brand is your 21 circuit wire harness?  Does it have an integrated fuse block with modern fuses or glass fuses? Are you trying to restore it with updated electrical system or is this going to be a driver?  This all makes a difference how you go about your wiring project. 

This is going to be a big task and take some time to do it properly. If you are trying a for restored look, use the OE firewall loom hole and grommet.  If not, this is how I did it on the '40 Caddy.  I used a Painless kit.  I mounted the fuse block in the center of the firewall out of the way, but easy to access.  If you want to make the wire harnesses to look like OE, wrap each indivdual harness with a cloth tape. GM has a very good strong tape to use for this.  Wrapping the harnesses is very time consuming, but can look great, but it is hard to access the wires if you need to trouble shoot or repair a circuit.  If not, what I use is plastic conduit.  3/8", 1/2" & 3/4".  These sizes will all of your harnesses. Use the small size that will accomodate the harness but leave a little room in it.  I divided the wiring into 5 harnesses. Dash, left front lighting, right front lighting, engine, and rear lighting.  After I have all the wires laid out in each harness, I use small zip ties about 12"-18" apart to keep the wires together neatly in the conduit.  I used a holesaw to make 3 holes for grommets in the firewall. One on the lower left side of firewall, another on the lower right side of the firewall, and the last in the lower middle of the firewall. The left is for the left front lights and horns (if on the left side), right is for right lighting and horns if on the right side.  The middle is for the engine wiring.  If you need to split some wire off the main part of the harness, there are Tee's available that are sized for the main loom and has a 90 which is smaller. Example: 3/4"x3/4" with a 1/2" out of the side.  There are also retainers sized for size of conduit. They either mount with a screw or you drill a hole a push xmas tree into the hole, snap the clip and your harness is secure.

If there is room, the rear lighting/accessory harness can be run down either the left or right side under the sill plates. If not, run it down the middle on either side of the tunnel. Once inside the trunk you can spilt it off to both sides, fuel tank, license plate light, etc.

Dash wiring: As mentioned in an earlier post, the ammeter, coolant temp, and oil pressure are all mechanical and the 12V system will not affect their operation.  The OE switches, if working OK, do not need replaced.  The 6V switches are designed to carry more current, higher amperage, than the 12V components. As mentioned earlier, use voltage reducers for the clock, OE tube radio, and fuel guage.

The heater blower motor, if it is quiet and runs OK, you can get a 12V to 6V reducer for it. If a 12V replacement is available and not excessively priced, I would replace it. The blower motor resistor will be OK. I would use the 6V blower motor relay and the horn relay until they fail.

I think that's all for now.  If any questions or need some help, just post and I will answer as soon as I can.

GOOD LUCK!