1968 Mercruiser 120 2.5

[RMELAN]

Just bought a project boat. 1968 Glasspar 18’ Flying V with a Mercruiser 120 2.5 inboard engine. Problem is it won’t crank using ignition key. I jumped the starter and it cranks over. I’m not familiar with the wiring but I have two wires coming out of the wiring harness by the starter that are not connected. There are purple and light blue. Any clues as to where they shou be connected?

 

[Scott Danforth]

first, welcome aboard.

next, I suggest you start with the manual. in addition to the stickies at the tops of the forums, the manual can be viewed on-line at this site:http://boatinfo.no/lib/library.html

you will need to service your points, etc.

 

[alldodge]

The Blue and purple wires should go To and From the voltage regulator and the Alternator
The pic below doesn't show the Blue and purple but the wiring is close enough to use. The Blue is shown going over to the ALT but not the Purple. It does and I can copy a pic of yours later if needed

I jumped the starter and it cranks over.

Have you tried to jump the starter at the Slave solenoid. When the key is turned to start the key passes 12V thru the Yellow wire to the slave solenoid.

To jump the starter from the Slave, jump 12V to the small terminal wire on it

 

[RMELAN]

Thanks so much for the tip! I’ll heck out the manual.

 

[RMELAN]

Here's the photo of blue and purple wire not connected and coming from the tilt-trim hydraulic pump assembly wiring harness. Also shown is the back of the alternator connections. I'm not sure how the purple wire connects to the Alternator?

 

[alldodge]

That is the trim wining, so it has nothing to do with the motor
For now just disregard them. After the motor is running good we can look into them more if you want.

 

[RMELAN]

I noticed on the wiring diagram for engines with an Ammeter, like mine, the purple/blue is not used. Its only used for a indicator light. If I jump the starter at the slave solenoid and it cranks what will that tell me? I read that if I jump the main solenoid large red wire with the yellow/red wire and it cranks the is the key switch that is bad (I did this and it cranked)? I did I also read the gear starter protection switch could be bad?

 

[alldodge]

I noticed on the wiring diagram for engines with an Ammeter, like mine, the purple/blue is not used. Its only used for a indicator light.

Looks like the Blue goes to the rocker switch, but unsure right now if the purple is for a light or not

If I jump the starter at the slave solenoid and it cranks what will that tell me? I read that if I jump the main solenoid large red wire with the yellow/red wire and it cranks the is the key switch that is bad (I did this and it cranked)?

Since it works when jumping the slave, this tells that power is not coming from the key. It could be the key, or the wiring leading to the key or coming from back to the motor. The engine connector could also be the cause.

Use a voltmeter and measure power at the key. Then turn key to ON and see if 12V shows up on the White (Ignition) wire. If that is good then turn to Start and see if 12V shows up on the Yellow wire

I did I also read the gear starter protection switch could be bad?

Don't know what that is, have not heard anything like it

 

[RMELAN]

Thanks for the tip! Power was not coming from the key. There is a neutral safety switch attached to the shift lever. see diagram. I bypassed that and now the engine cranks over with the key but does not start. I took a spark plug out and cranked the engine and there is no spark?

 

[Scott Danforth]

did you service the points? if the boat sat for more than a few months, you need to file the points, re-gap them, verify the dwell, then set timing.

 

[RMELAN]

I haven’t got into the distributor yet. The prior owner said it sat for two years so plugs points timing needs to be done.

 

[RMELAN]

Any ideas as to where to buy parts? I’d like to replace cap rotor plugs wires points, etc.

 

[alldodge]

This link list all the parts and numbers. Can either buy from them or search for part numbers on line

https://www.mercruiserparts.com/bam/subassembly/30879/1559/20