1988 Merc 35HP Outboard starting troubleshooting

[sluffmeister]

I have a 35 HP Mercury outboard serial number OB356820 that has intermittent starting issues. Most times when I turn over the key the motor starts fine. However, 20% of the time it doesn't turn over at all. t'm looking for the next steps in troubleshooting to determine the defective part. Here's what I've done so far. I installed a brand new battery, I replaced the starter with a used starter. When the motor won't turn over, I can get it to crank over just fine by using jumper cables from the positive terminal on the battery to the starter side of the solenoid. I didn't have a screwdriver handy, but when it wouldn't turnover I tried using the jumper cables on each terminal of the solenoid to bypass it, and it didn't crank when we turned the key. Could this be a solenoid issue? Key switch? What other tests should I try to narrow this down? Thanks for any suggestions.

 

[Chinewalker]

Try gently tapping the solenoid. Might be getting sticky with age. Make sure all battery cable connections are clean and tight.