Merc 165 ignition Wire problem. Please help.

etherealstorm · Mar 16, 2011

I just picked up an old 1975 Bayliner with a Mercruiser 165 inline 6. Engine turns over, but I have no spark. Then I found a couple of wires from the ignition coil have been cut, and I have no idea where they go. I have a shop manual, but the schematic shows wires going to a shift interlock switch. I'm a newbie. What is that? doesn't help that the manual is showing different colered wires than those that are actually on my craft.
If anyone has any images of the wiring for this engine, or could take a picture of thier 165 for me. I would love the help.
Thank you in advance.mercrus

86 century · Mar 16, 2011

Re: Merc 165 ignition Wire problem. Please help.

There should be three wires connected to the coil. Switched power to the pos; lead form points and shift interrupter on the neg side.

I have seen two or three different colors for the switched hot. The lead from the points will be black. lead from shift interrupter should be gray.

The shift interrupter is a switch activated by you shift cable to momentarily stall the eng so the drive will shift easier.

Hope this helps
Good Luck

Don S · Mar 16, 2011

Re: Merc 165 ignition Wire problem. Please help.

86 century said:
There should be three wires connected to the coil.

On a 75 mercruiser 165, there are actually 5 wires going to the coil, not counting the center high voltage lead.
See the picture below.
On the positive side, you have the resistor wire and the tan wire going to the starter.
On the negative side, you have 3 brown wires, one to the shift interrupt switch, one to the tachometer, and one to the distributor.
The gray wire was not used on the 165 l6 engine and was for the tachometer on the ones it was used on.

etherealstorm · Mar 16, 2011

Re: Merc 165 ignition Wire problem. Please help.

Thank you guys for the help. Where would I find the shift interupt switch? I have the same diagram in my shop manual, but thank you for clearifying for me. Like I said, I am really new to all this so all your help is greatly appreciated.

ziggy · Mar 17, 2011

Re: Merc 165 ignition Wire problem. Please help.

Where would I find the shift interupt switch?

find the lower shift cable inside the boat and follow it up to the shift plate. there you will find the shift interrupt switch. be carfeful with it. it's nla (no longer available).

follow the brown (looks kinda orange in my pic) and black wire in the pic. they go to that dusty looking shift interrupt switch. the switch is operated by a v looking block of metal with a big spring on it. the roller on the switch lever sits in the valley of the v..

achris · Mar 17, 2011

Re: Merc 165 ignition Wire problem. Please help.

As a newbie to the wonderful (and oft confusing) world of the Mercruiser shift cutout switch (can't spell the other word)...

You DEFINITELY need to read this article..

http://forums.iboats.com/showthread.php?p=1930449#post1930449

Chris.......

Fishermark · Mar 18, 2011

Re: Merc 165 ignition Wire problem. Please help.

And to your problem of no spark....

You can take the switch entirely out of the equation while you get your spark issue solved. The switch is designed to momentarily ground out your coil and cause the engine to stumble or hesitate. Your no spark issue may be as simple as glazed or pitted points. Especially if the engine has sat unused for a long period of time.

I believe there is a post on points style ignition at the top of the page - under the "adults only" section. That would be helpful reading as well.

Once you get the spark back and the engine running, make sure your switch is connected and working. It will be needed to get the outdrive out of gear. (Sometimes people disconnect the switch because the engine was dying when shifting, and they think the switch is the fault).

etherealstorm · Mar 30, 2011

Re: Merc 165 ignition Wire problem. Please help.

Thanks everyone for your help. I think I have all the wires correct for the coil now. But still no spark. Guess I'll try a new Distributor cap, rotor, and new coil. Now... Does anyone know where I can get those? The only ones I can find are for a thunderbolt ignition, and I'm not even sure if I have that. And more pictures please. Those helped big time.
Again, thanks to all.

Bondo · Mar 30, 2011

Re: Merc 165 ignition Wire problem. Please help.

I think I have all the wires correct for the coil now. But still no spark. Guess I'll try a new Distributor cap, rotor, and new coil.

Ayuh,... Don't just go throwin' parts at it,...

Diagnose it...

What do the Points look like,..?? Are they Working,..??

etherealstorm · Mar 30, 2011

Re: Merc 165 ignition Wire problem. Please help.

The points all look good, but I'm going to check it all with my volt meter just to be safe before placing any order. The biggest issue is that a lot of the wires have been cut, and I need to reroute everything, and the schematics only tell you so much.

Fishermark · Mar 30, 2011

Re: Merc 165 ignition Wire problem. Please help.

As I mentioned above, you can bypass much of the wiring in order to diagose things. Simply supply switched 12 volts to the positive side (so you can turn it off after it starts) and hook up the wire from the points to the negative side. Then try and start it. If it starts, at least you know the ignition works - then you can work out the wiring.

Lyle29464 · Mar 30, 2011

Re: Merc 165 ignition Wire problem. Please help.

86 century said:
There should be three wires connected to the coil. Switched power to the pos; lead form points and shift interrupter on the neg side.

You should not abbreviate positive in this thread.

ziggy · Mar 30, 2011

Re: Merc 165 ignition Wire problem. Please help.

heres a link to another good read. it's about how to tune up your points type ign. systems. http://forums.iboats.com/showthread.php?t=335302 the link is from the adults only sticky #18.

also, don't look at your points and assume good. run some emery over them to shine off any tarninshing that may have occured preventing contact. then do replace the points. they are a spring tune up item to be replaced yearly imho. i also replace the cap, rotor, condensor, plugs and a fuel filter yearly as part of my summerization process....

dalegrimes · Apr 17, 2011

Re: Merc 165 ignition Wire problem. Please help.

try to isolate the problem by having only the wire to the distributor on the neg side. leave the other wire off, which is probably the gray wire. this has definitely worked for me.

Merc 165 ignition Wire problem. Please help.

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