1988 Merc 70 HP wiring problems

[1988Merc70]

Bought a used Harris 'toon with a 1988 70 HP Merc. Drove it for about 4 hours and it started not wanting to start. Blowing the 20 AMP fuse and won't start at all. Installed a new key switch, installed a replacement starter and starter solenoid and lubed shift and throttle cables and the engine pivot point.

A Marine mechanic did some of the work and after it continued failing he recommended replacing the control box. However he had health concerns and bowed out. No other marine mechanic available to work on 37 year old Merc..

So I'm working on it, pulled the wiring harness and control box to test indoors, too cold outside to do anything. Plan to test all wires with jerry rigged light bulbs to find broken or shorted wires in the harness.

Question: Don't really need trim/tilt, toggle kill switch, tilt indicator, audible for low oil, light switch, etc. All we need is a starter switch and a choke (3 wires).

Can a guy run the motor without the 5 pin cable to the console, unplugged? Comments on blogs say the China made control boxes are not reliable. IF the wiring harness is failed can a new wiring setup be purchased?

We just need basic operations for use on a smaller lake in the Brainerd Minnesota area.

Thanks for any assistance.

Tim C.

 

[Chris1956]

Since the motor does not use any battery power to create spark, the blown fuse suggests a bad wiring harness or a short.
What is the condition of the wiring harness for the engine? A lot of them fail by now, if not replaced. Failing wiring harnesses can ruin the other igntion components.

 

[1988Merc70]

Used a car battery to put 12v fused on the center pin on the motor end of the harness (cannon plug). With the 5 pin console plug unplugged the light switch is green with oxidation. Then exercised the switches on the control box monitoring cannon plug pins. Trim & Tilt both work (they are on separate wires outside the cannon plug). 12v is delivered when the switch is on. Choke works when key is pushed in. And the start switch works, after the neutral cutoff wire (neutral start switch) was attached to the slide on connector (explains why it wouldn't start).

When I say work I mean there is power at the cannon plug when a switch is closed. Doing this testing on the control box and harness removed from the boat. The boat is 2.5 hours away.

Planning to tidy up the control box wiring and make a trip to the boat on a warm up day next week and see if it works.

See the corroded green light switch on the left of the attached pic of the back of the console.

I'll take a hard look at engine wiring for any problems.

Would it be smart to spread the split pins on the cannon plug. To make sure they making contact? Or is there a better way to ensure there is good contact in the plug?

Thanks.