Direct wiring the coils to the battery using
a relay to bypass the wiring harness and
give more voltage to the coils.
This mod would be used generally for older bikes that have questionable wiring. A quick way to know if this will help your situation, is to measure voltage at the battery with ignition on, bike not running. Should be around 12.5 volts. Then measure voltage on the red coil power wire, again with ignition on and bike not running. If you have less than 12 volts here, you are losing voltage somewhere in your wiring, through the numerous switches and connectors before getting to the coils. I did this now on my 2002 just to test it and see if it would help the hot starting problem. So far it, combined with moving my regulator/rectifier, seems to have made all the difference in the world. Time will tell.
Basic automotive relay. Can be found in the bling section of your auto parts store.
Inline fuse holder. I prefer the waterproof mini fulse holder for this.
10amp mini fuse
12-14 guage wire, red and black
Various spade connectors and ring connectors, crimp type for 12-14 guage wire
Soldering iron and solder
I borrowed this diagram from folks at KZrider.com, where I am also a member. Note: Our VN750's have RED wires connecting the coils to power, not Red/Yellow as in the diagram. Another note, my relay had #30 instead of #36 on the Power connector.
Remove the front left side panel that is located above the left air filter. There are two phillips screws holding this panel on. It's the panel with the reflector on it, in front of the fuel tank. This side panel is covering the front coil.
A. Automotive relay
B. Original rear coil power wire, going to relay as the trigger.
C. New power wire going to both coils. You can't see the junction where I soldered this wire to the same gauge wire going to each coil as it is under the large wire cluster that you can see at the bottom.
D. Inline fuse holder.
E. Ground wire
Fish a red 12-14 guage wire up from the battery box area to the front coil. (C Figure 2) Leave yourself extra wire at the battery box end, enough to be able to attach this end to your relay (A Figure 2). I put my relay in the right front corner of the battery box area, taped to my frame. You might have to loosen the fuel tank and raise it slightly to fish this wire through. Make sure it stays under the frame where it won't have the tank sitting on it. Strip the wire and tin the tip with solder. Crimp on a female spade connector. I used spade connectors that have a cover over the entire connector. Pull the red wire off the coil, put some dielectric grease on the new connector and connect the new wire onto the coil. Wrap the old connector in black electrical tape and push it under the frame. I didn't cut any existing wires to do this mod. It can be reversed easily if needed.
Reinstall the side cover over the coil. Measure from the power terminal of the back coil to a location where it can intersect with the new front wire you just installed and cut another piece of red wire. Mine was about 8" long. Strip both ends of the 8" wire. Taking the wire you attached to the front coil, find an area of this wire where the 8" wire can intersect with it, and cut the long wire, and strip the end. Now using the rest of the wire you just cut, strip it's end and join all three ends, (end from wire from front coil, end of 8" wire, and other end of wire you are going to use to go to the relay) and twist them together. Tin the twisted wire with plenty of solder, then shrink wrap and tape the connection. Tin the other end of the 8" wire and crimp another female spade connector to the end. Remove the existing red power wire from the rear coil, dab a little dielectric grease on the new connector and connect the spade connector from the 8" wire to the power terminal of the rear coil.
The remaining end of wire coming from that 3 way junction you soldered, (C Figure 2) needs to be stripped and tinned, and a female spade connector crimped on, DE greased and connected to the terminal on the relay labeled 87. This is your power to the coils from the relay.
Pull the tape back on the original red wire (from the rear coil) (B Figure 2) to give you enough slack to be able to reach the relay with the wire. Again, dab a little DE grease in the connector and connect this original red coil power wire to the post on the relay numbered 86. This original wire will now be used as the trigger to close the contacts in the relay when the key is turned on.
Tin the leads on both ends of the inline fuse holder (D Figure 2) and on one end crimp a ring connector that is large enough to fit the battery terminal screw through it. On the other end, crimp another female spade connector, dab some DE grease and connect the spade connector to the terminal on the relay labeled 36 or 30, depending on which relay you have. Insert your 10 amp fuse into the fuse holder and close the rubber top.
Take a piece of 12-14 guage black wire and cut a piece long enough to reach the relay (E Figure 2), and go to the grounding point on the right side of the frame (A Figure 3), above the starter relay. Strip and tin the ends and on one end crimp another spade connector and dab DE grease into it and attach it to the terminal on the relay labeled 85. Remove the bolt holding the ground to the frame, clean the area with a wire brush (I used my dremmel with a wire brush tool--wear safety glasses as these little wires become missiles!) and attach the ground wire and the new black ground wire going to the relay, and tighten well.
Now take the other end of your inline fuse wire with the ring connector and put it over the positive battery terminal and connect the battery terminal bolt and tighten very tight.
Attach your battery ground wire and tighten well.
I wrapped black tape around the relay and all the wiring connections and then taped the relay to the right side frame in front of the battery.
Some side notes: While doing this mod, I noticed that the starter relay positive terminal was rusty (B Figure 3) so I pulled it apart and cleaned the connection well. There is also a two prong connector that plugs into the starter relay and I pulled it off and the terminals were corroded so I cleaned them up as well, used DE grease on them and put them back together. Just things you should check while you are in there doing this stuff.
That's it. Now your power to the coils comes directly from your battery so weak wiring no longer comes into play, and maybe it will have a positive impact on the hot starting issue as well.