1978 Mercury 115 hp

[ajsumms]

I am looking for an inexpensive wiring harness. I need the internal harness. I know that the CDI 414-2770 is a replacement but, it replaces a number of other harness' which are cheaper. What is the difference and can I use ant of the other ones? I was on a different site and they told me that 84-74904 was for a 20 hp motor but the CDI replacement will work on it and my 115. I'm just weighing my options before buying. Thanks

 

[SeaKaye12]

Re: 1978 Mercury 115 hp

AJ....I made my own. The wires as they came from the plug were good enough to splice onto. Did a good soldersplice which I covered in heat-shrink tubing. Way cheaper than any harness...and it was really pretty easy.

Chuck

 

[ajsumms]

Re: 1978 Mercury 115 hp

I did the same thing this evening. I'm going to see if it worked in the morning. There was a red wire, it was an 8 gauge wire I think, it came off the harness as a single wire. They soldered another onto the wire and split it. One wire went to the switch box and the other went to a relay I think. Does anybody know if this is a factory splice? I just ran one wire to the relay and then I ran another jumper over to the switch box. Will this hurt anything?

 

[Chris1956]

Re: 1978 Mercury 115 hp

The red wire runs to the switchbox on a distributor ign motor. The other red wire that is spliced to it runs to the rectifier.

Yellow is starter solenoid, Black is case ground, grey is choke, brown is tach signal, orange or salmon is ign killer on ADI ignition, unused on distributor ign motors. White is ign accessory power.

Try surplusunlimited for a new wiring harness if you need it.

 

[ajsumms]

Re: 1978 Mercury 115 hp

So, my question would be.... Does it matter if I splice into the wire or is it ok the way I did it? I ran the wire to the rectifier and then jumped over to the switch box.

 

[Chris1956]

Re: 1978 Mercury 115 hp

That is fine.....

 

[ajsumms]

Re: 1978 Mercury 115 hp

ok cool.... It had rained here so I haven't been out yet. I still need to clean up some wiring inside the boat yet. I'm not sure what the PO has done in there. He has a bilge pump and I think at one point had other electronics in there. I'll post what happens when I fire it up.

 

[ajsumms]

Re: 1978 Mercury 115 hp

YEAH!!! The wiring works. As far as I can tell its still charging. Now I found that I have to lift the fast idle lever almost all the way forward to get a response. I'm going to look and see if I can adjust it anyhow. Does anybody have any hints or can you tell me more about adjusting the throttle cables? I know it advances the timing and I dont want to mess anything up. When I put it into gear it won't idle up till I get almost all the way forward either. I'm going to change the oil in the lower unit. Is there any adjustment on this? What is the top RPM on this engine? I'm still very new with marine engines. Also, I noticed at idle I am not getting water from the pee hole on the side. When I idle it up I get a nice solid stream. Is this normal? Sorry as I said I'm new to this and I am looking for any and all pointers. Thanks!!!

 

[Chris1956]

Re: 1978 Mercury 115 hp

There is a lot of movement in the MerControls before the throttle advances. Let's say neutral is at 12:00. Forward at idle speed is 10:30 and WOT is~ 8:00. Push the throttle al the way forward (motor off) and see if the carbs are all the way open. Max RPM is 5500 or so. The telltale should show a good stream at all RPM. Maybe the impeller needs to be replaced? If you do not know the last time it was done, then it is due now....

 

[ajsumms]

Re: 1978 Mercury 115 hp

I went through the wiring and I'm going to have to rewire the tach and lights. I appreciate your help. That is exactly where my controls are responding. I still have some wiring and a couple seats to recover before I get it out on the water to test it out. I have ran it for a good 20 mins in the drive way with the hose hooked to it. I'm thinking I might do the impeller just to make sure. I am getting a really good stream out of the telltale when it is idled up just a touch but when I'm at idle there is nothing. When I bought it he said the shop told him everything was good except for the wiring harness. In other words I have no idea when the impeller was changed. If I pull the lower end off then I can kinda check that too. Thanks again for your help.

 

[Chris1956]

Re: 1978 Mercury 115 hp

Don't check the impeller, replace it. Also replace the two gaskets that sandwich the wear plate and the wear plate itself. If the gearoil shows signs of milkiness, replace it and replace the water pump base (it has the driveshaft seal), and the gaskets on the fill and vent plugs.