Question. If I replace the turn signal bulbs is it correct that two 1157 dual filament bulbs go in the front and two 1156 single filament bulbs go in the rear? What will happen if you use four dual filament bulbs instead? Thanks.
Do not know about a Deuce, but on most bikes that is the case.
The 1157 has off set Bayonets on it and two contacts offset from center. The 1156 has the bayonets directly opposite each other on the bulb with a single center contact. You should not try and put an 1157 in an 1156 socket, you may get it in, but it will not work right and the socket may also get damaged in the process.
How tough is it to replace the sinle filament sockets in the rear with dual filament sockets and then wire the new filament to act as a running light like the front? I run Kuryakyn's mod in the back, but would rather have the change (increase) in intensity in the rear signals.
If you have a Heritage Classic, You can buy the front turn signal housing and put them on the rear.
You would have to add the wire for the running lamp but you should be able to wire that in at the taillight and just connect it to the taillight wire.
This would give you running lights in the rear.
Just solder all connections and cover all joints with good heat shrink. See the electrical section for good tips on wire splicing.