'76 Merc 85hp Wiring from Engine to Control Box Help

[Chris1956]

Your motor does not have overheat sensors, and therefore doesn't need a horn. The horn would sound if the sensor wire is grounded. I would trace it back and see where it is shorted.

Make sure the ign killer wire is not shorted to ground, when you want the motor to have spark.

 

[Dentcrew]

I try and trace that Tan/Blue Stripe wire back inside the control box. As this is a newer model control box and newer harness from control box to engine, that may just be a wire that does not go anywhere to my older engine, as I have 7 wires from the engine, and 8 from the newer control box. I just don't know if the 8th wire ( Tan/Blue Stripe ) need to be tied into any of the 7 engine wires.

 

[Dentcrew]

Wondering if I wired just the red and black wires off the control box, and remote started the motor ( bypassing the control box ) to rule out any control box issues?

 

[Chris1956]

That sounds like a plan. Disconnect all control box wiring. Choke the motor manually,and crank the motor by jumpering the starter solenoid, and see if she starts.

 

[Dentcrew]

Dang, another no go. No Spark still. So it appears to NOT be something in the control box wiring. I suspect trigger or Switch Box. Question, when I go to check Ohms on the trigger wire ( 4 ), am I checking each wire against each other without using a ground? Like Purple against the white, brown and Black/white etc for each color )?

 

[Chris1956]

These ohm tests are from a motor a bit newer that yours. I would expect them to be close or exact. Unfortunately I lost my manual for exactly your motor in the flood..

9/18/24 AMPERE STATORS (4 CYLINDER)
Test Leads Resistance (OHMS)
Between Blue Stator Lead and Blue/White Stator Lead (Low Speed) 6800-7600 (90-140) 6.8-7.6 (R x 1000)
Between Red Stator Lead and Red/White Stator Lead* (HiSpeed) 90-140 90-140 (R x 1)

* Connect test lead to black stator lead if stator is removed from engine. NOTE: Above readings are for a cold engine (room temperature). Resistance will increase slightly, if engine is warm. 3. If meter readings are other than specified, replace stator assembly.

TRIGGER TEST (4 CYLINDER) 1. Disconnect all trigger leads from switch box. 2. Use an Ohmmeter and perform the following tests.

Between Brown Trigger Lead and Black Trigger Lead 700-1000 7-10 (R x 100)
Between White Trigger Lead and Violet Trigger Lead 700-1000 7-10 (R x 100)

NOTE: Above readings are for a cold engine (room temperature). Resistance will increase slightly, if engine is warm. 3. If meter readings are not as specified, replace trigger

 

[Dentcrew]

Should I use the 20K Ohm setting for this test?

 

[Dentcrew]

I disconnected all 4 trigger wires from the switch box. I got 850 for the Violet to White and got 854 for the Black to Brown at the 2000ohm setting, so I think the trigger is good?

 

[Dentcrew]

With all 4 stator wires disconnected, I got 6.14 @ 200K for the Blue - Blue/White and I got 149 @2000 for the Red - Red/White. Not sure why I got got such a high reading on the Reds? Although, I'm not well versed in the Ohms Measurements which is why I posted where the switch was at for the readings.