Since it is an 85 the ignition is probably dirty and worn. Before buying a new one and getting it rekeyed and everything you might try rebuilding.
Here's a write-up by kent4chaos from the VN750 Yahoo group for doing just that
REBUILDING THE IGNITION SWITCH ON A VN750
My 1991 Vn750 developed a "dead spot" in the ignition switch
which would cause the dash lights to flicker or go out completely.
For two years I lived with this problem and temporarily solved
it each time it would occur by slightly turning the key towards
the off position. It worsened to the point where the defective switch
would cause the bike to begin stalling - something had to be done. A
new switch is about 70 bucks, plus I didn't want to have to
deal with having to re-key my bike.
10mm socket/drive or nut driver
#2 phillips screwdriver
medium sized jewelers scredriver
6mm Hex driver/hex key/allen wrench
small needle nosed pliers
1. Remove the windshield (if applicable).
2. Remove the headlight.
2a. Remove the 2 phillips head screws that hold the front portion
of the headlight to the bucket - the screws are located about 4 o'clock
and 8 o'clock (be sure not to mess with the adjusting screw located
2b. Remove the headlight lens and trim ring from the bucket - pull
the bottom free which should allow you to "un-clip" the top portion.
Disconnect the three prong connector from the lightbulb and place
the lens assembly somewhere safe.
3b. Using the 12mm wrench on the nuts on the insides of the bucket,
remove the 10mm hex headed bots that secure the bucket to the ears.
Carefully allow the bucket to hang down from the wires.
3. Remove the instrument cluster/gages.
3a. Remove the 2 bolts (1 on either side) of the "lights cluster".
3b. carefully remove the gauges and cluster
(allow to dangle from the wires).
3c. Remove the black rubber boot from around the outside of the
ignition switch post.
4. Remove the switch assembly - there are two socket
head cap screws under the top fork clamp - after removing the
bolts you should be able to "fanagle" the switch out of the fork
It has been brought to my attention that if the handlebars are turned to the full left position, it is much easier to remove the switch without "fanagling".
5. Remove the two brass colored phillips screws from the plastic
body of the switch. Separate the electric switch portion from
the mechanical portion.
6. Carefully snap the plastic cover off the back of the switch -
check each of the solders carefully to make sure none have broken free.
7. While holding the switch "circuit board side up" carefully pry the
plasic body away from the circuit board where the little tang locks the
two pieces together - CAREFUL! - AS YOU SEPARATE THE TWO PIECES BE
CERTAIN NOT TO TURN OVER THE SWITCH PORTION, THERE ARE SEVERAL SMALL
PIECES THAT COULD FALL OUT!!!
8. Take the switch portion (should now be free from the bike) to a
suitable location to work on it (ie. workbench).
9. One at a time, remove the contacts from the switch and slightly
stretch the compression spring open a little bit.
10. Use contact cleaner to clean each of the contact points as well
as the contact paths (on the circuit board).
1. Do everything you just did in the reverse order.
Hope this helps someone - kent4chaos
Patriot Guard Rider
2000 VN750 Sere (Serendipity)
1990 GL1500 (Ole Blue)
1986 VN750 EVie (project bike, heavy custom)
VROC # 11628 / 25000-H
ARVROC # 12 Coordinator and Crowd Control
OKVROC # 18 (H)
TNVROC # 45 (H)