Intermittent no start - '76 Mercury 850 Thunderbolt

[JF660R]

Bought a Starcraft last year and fixed a runs on 2 cylinder issue by replacing the switch box, with a Chinese unit. Ran good all summer. First few trips this year it started leaving us stranded. Would start and run good away from the dock, but once shut off would not restart. No spark.

Recently replaced the trigger to no effect, and with voltage into the switch box but not out...replaced the box again with a more quality unit. We then got the motor started again and had spark on all 4. Restarted it many times while dialing in the timing in the tank. Buttoned it back up and just about to run to the lake for a test, one more time to be sure and.... no start. No spark. OMG! Can I just get rid of all this '70s electronics BS and make this thing run!?

It's got good compression and runs good, when it runs. But it's about to get scrapped!

 

[Chris1956]

Gee, You have ADI ignition. The electronics on that motor were used for decades. Maybe even today. I would start with the engine wiring harness and connections, as that is likely where your issue is. Disconnect the ign killer wire. Originally it was orange or salmon. If the wiring was updated, it could be black/yellow.

 

[JF660R]

It very well could be wiring gremlins. But I haven't seen a replacement harness. We inspected wiring pretty closely while we had the fly wheel off. We've tried disconnecting the tilt switch and such. The serial number is 4537364 and it is the 4 coil set up.

Found this guide http://outboardparts.com/troubleshooting/troubleshooting10.htm that I'm gonna look at. Just getting burnt out on spending my Saturdays wrenching rather than on the lake.

Looking hard at a '93 65hp Suzuki on CL. Probably a whole different can of worms.

 

[Chris1956]

When I last looked, engine wiring harnesses were avail on the web. I think you use a 73362A1 on your motor, plus a 74901 grounding cable harness.

 

[JF660R]

I'm seeing that as NLA ... maybe I'm looking at the wrong sites.

Here on iBoats there is 414-3369 for the main harness but $163. Gotta decide where to draw the $ line on this old motor.

 

[Chris1956]

The iboats part number looks to be the boat harness, not the motor harness. Try surplusunlimited and see what they have. You want the engine harness from the quick disconnect plug (male) to the switchbox, starter solenoid, choke, rectifier and other things. Maybe you can graft new wires to the quick disconnect plug?

 

[Faztbullet]

Don't waste more $$$$ on a harness as it sounds like your stator is failing. Download the CDI troubleshooting manual and check the stator voltage when it has no spark