Re: 1978 Merc 700/70hp 3 cyl. wiring harness issue
Sorry I can't help with the wiring colors/functions on the 1986 control box, but here is the diagram for the 1978 70hp 3cyl:
http://www.maxrules.com/oldmercs/Wiring/1966ona/54.jpg
Someone else will have to find you the 1986's diagram.
As I see it, you got three options:
1) Does your 1978 motor
have the internal harness? If so, you may be in luck. I have a 7-pin flat harness connector cut off the external harness / control box from a 1978 Merc 70hp 3 cyl. with about 6 inches of all wires on it. You could butt splice that into your current control box / external harness (once you have a verified diagram for your 1986 box) and be in business. Just pay shipping and it's yours.
2) If you still have (or can find, say on EBAY) an internal harness that would plug into your current external harness: cut off the plug, get some wire, 3-way butts and ring terminals, and rig it up into an internal harness for the 1978 70hp yourself.
3) Do what I did: get rid of those connectors and internal harness entirely, get some ring terminals and 3-way butts, and just extend all the external harness wiring right into the cowling:
http://forums.iboats.com/showthread.php?t=387130&highlight=harness
I suggest the third option if you have a few extra feet of harness, because in my experience that specific flat connector on the 1977-79 Merc 70hp 3cyl is prone to internal shorting and is unreliable (I went through three used internal harnesses shorting inside the plug before wising up
)
If your 1978 motor does not have the internal harness, and you decide to make your own (or extend the external), I have all the individual wire length measurements you'd need to make a faux internal harness for the 1978 70hp 3 cyl.
