1976 Mercury 850 Control Box REWIRE help!

[850Merc]

I recently purchased a new OEM external wiring harness for my 850 Thunderbolt and now I have the job of rewiring the control box (soldering and replacing old with new). The old harness was in terrible shape, the boat has been sitting for about 16 years (at least that the last time it got new tags).

I have yet to open the control box, but a guy at the local Mercury shop (Mercs and More) here in Denver said that it usually ends up taking him about 4 hours to rewire a control box.

The harness only comes with 4 or 5 wires that feed in to the control box, I was wondering if anyone here has some advice for me during this process? or perhaps an exploded wiring diagram for reference?

 

[carholme]

Re: 1976 Mercury 850 Control Box REWIRE help!

You haven't provided your engine s/n but if it is a '76 and a three cylinder this one should do it.

http://www.maxrules.com/oldmercs/Wiring/1966ona/29.jpg

Gerry

 

[850Merc]

Re: 1976 Mercury 850 Control Box REWIRE help!

This is exactly what I need, thanks Car!! Sorry for the lack of s/n...

The new harness came via UPS yesterday, it looks great. I don't think that they still make this harness, it must be new/old stock. It's definitely quicksilver though.







I have a friend who is pretty handy with a soldering iron, so this diagram is going to be very valuable. I think is is a 4 cylinder 850, but I'm sure the 650 control box wiring diagram is the same, plus I have the old one to look at while we're replacing it. I may try to add more pictures of the process. Tomorrow night we are going to start working on it.

 

[carholme]

Re: 1976 Mercury 850 Control Box REWIRE help!

If it is a four cylinder:

http://www.maxrules.com/oldmercs/Wiring/1966ona/30.gif

Gerry

 

[Chris1956]

Re: 1976 Mercury 850 Control Box REWIRE help!

That '76 motor should have the old wiring colors. If the new harness has the new wire colors, you will need to use an newer wiring harness skematic. If that motor is the 4 coil ADI ignition (should be), you can use an 1980 or newer 4 or 6 cylinder motor wiring skematic.

 

[850Merc]

Re: 1976 Mercury 850 Control Box REWIRE help!

We took apart the control box on Friday night and discovered it needed a few things. bushings, detente rollor and found out yesterday it needs a new ignition switch. When we were removing the old wiring (via soldering iron) we must have gotten the base of the ignition switch too hot. I went down to Mercs and More on Saturday and picked up the detent and bushings, now I have to run back over there today and pick up the ignition switch. After quite a bit of research it seems that there are really only two types of ignition switches for these old control boxes. Push to choke (I assume this means you push the key in while starting to choke it) which has 6 poles, and the separate choke button version (which I have) that uses only 5 poles.

Couple pics











Should have this thing back together tomorrow night, and that may be it for this thread. Your help has been really appreciated, and the restore thread will continue on indefinitely (just kidding).

 

[850Merc]

Re: 1976 Mercury 850 Control Box REWIRE help!

New switch is installed. Everything cleaned, greased (with waterproof grease) and put back together. For the record, I just watched, my friend (and PO) did all the work on this one. Really happy to have it done and ready to go back in the boat. With the new harness, switch, gasket and detente roller, the control box owes me about $230.

 

[GA_Boater]

Re: 1976 Mercury 850 Control Box REWIRE help!

You are lucky to have a place right down the street to get parts. Is Mercs and More well stocked with parts for these old girls?

 

[Chris1956]

Re: 1976 Mercury 850 Control Box REWIRE help!

Just so you know. The original wiring harness was tinned marine-grade wire. The new one you have is copper. Don't expect 40 years out of it, if you boat in the salt. Ironically, the new harness has the old wiring colors, which makes it easier for you.

Good luck with it. I always thought the 850 was a pretty good motor. Light weight and compact, with good power.

 

[850Merc]

Re: 1976 Mercury 850 Control Box REWIRE help!

You are lucky to have a place right down the street to get parts. Is Mercs and More well stocked with parts for these old girls?

Yes, they had everything I needed for this old Control Box. I think they have a large selection of NOS parts, they also do tune ups and major motor service. I have a feeling I'll be using them in the future for other things, really nice guys. Part of the warehouse was affected by the "historic" flooding that we had, but everything is cleaned up and looking good now.

Just so you know. The original wiring harness was tinned marine-grade wire. The new one you have is copper. Don't expect 40 years out of it, if you boat in the salt. Ironically, the new harness has the old wiring colors, which makes it easier for you.

Good luck with it. I always thought the 850 was a pretty good motor. Light weight and compact, with good power.

I noticed that the new wire was a smaller gauge than the old wire. Thankfully I'm 1000 miles from any salt, I just need to make sure to have decent sacrificial anodes in place for this thing. We also coated the connections in electrical grease before closing it up.