1972 100hp Oldie but (hopefully) a goodie- solenoid test

[dstom]

Well, I have been working on this oldie that does not start. Initially, there was no click when key in the start position. That has now been fixed and the starter motor engages, but runs very slowly. The following is the result of some voltage tests at the solenoid with various key positions. (solenoid in is the connection from the battery, solenoid out is the wire to the starter)

key position off on start
Solenoid in 0.00 12.96 3.85
solenoid out 0.00 n/m 3.83
Starter in 0.00 0.00 3.82

Furthermore, when I used jumpers straight to the starter (bypassing the solenoid), the starter engaged very quickly and firmly, and turned the motor over fine.

What other tests/checks should be done to verify that it is the solenoid?

Thanks for any and all assistance!

 

[samo_ott]

Re: 1972 100hp Oldie but (hopefully) a goodie- solenoid test

If the solenoid is clicking and the engine turns over, it's working fine. You need to look other places. Usually in the old engines the cables are original and the connections and wire poor. The first thing I woud do is disconnect every connection in the heavy pos and neg wires from the battery to the engine and clean each wire/junction until the joint is clean and shiny. If this does not do it then I would get a good known heavy gauge wire and start bypassing the wires one at a time until you find the weak wire. The old wires corroded on the inside of the insulation and sometimes you just cant tell where the problem is unless you replace em one at a time. Thus you might have to replace em all anyways but you can test em and find out. The good part is that you know the starter is good, so that's good as it's the expensive part. Good luck.

 

[HighTrim]

Re: 1972 100hp Oldie but (hopefully) a goodie- solenoid test

In addition to the good advice given above, be sure to remove/polish/tighten the main ground. Also ensure that your battery is fully charged and load tested. Any wires that crunch when you flex them are definately corroded internally. If you have a meter you can quickly voltage drop test all wiring to determine faulty sections. Solenoids are often replaced when in fact they work just fine. As steve said, take those connections apart and file the crap out of them, make them shine, then re tighten. Dont just inspect them visually. I do this myself every year on my motors regardless.

 

[jay_merrill]

Re: 1972 100hp Oldie but (hopefully) a goodie- solenoid test

The above advice sounds good and if you get the motor running without further problems, you might have a good outboard. That said, the 1972 OMC 100hp motors have battery-CD ignition, with a distributor system and amplifier. There are a number of NLA parts for this ignition setup and others that are extremely expensive.

The motor also has a hydro-electric shift system, which can be fine, but can also be a major problem if it doesn't work correctly.

Because of these issues, be sure to check out all of the systems, before spending a bunch of money on any one of them. The basic point is that you could have a decent motor and you could have a money pit - you just have to determine which.



???

 

[emdsapmgr]

Re: 1972 100hp Oldie but (hopefully) a goodie- solenoid test

After you have checked all of the above comments, it is possible the contacts inside the solenoid are corroded. The contacts may not be passing enough current to turn the starter. You may need to consider replacement of that solenoid.