Wiring problem on 350 mag Mercruiser Thunderbolt 4 (module on distributor)

[84EdH]

I am repowering a 1979 century that originally came with a Merc 228 set up. I am using a 1995 350 Mag to repower. The cannon plug on the engine does not match the cannon plug on the boat side. The new engine has a 10 pins, the old set up 9 pins. They do plug into each other. I have been trying to check and see if the plugs make the correct connections. I started with ground and am stumped. One of the large socket pockets on the engine cannon plug, shows continuity with ground. The boat side cannon plug that connects to that socket goes to a red wire ! This does not make sense to me. Also, there is no black wire on the engine side cannon plug at all. How is ground carried forward to the dash?

Anyone make sense of this?

Ed

 

[Don S]

Re: Wiring problem on 350 mag Mercruiser Thunderbolt 4 (module on distributor)

Let me guess, the 79 has an ammeter instead of a voltmeter on the dash correct?

What are the colors of the wires on your wiring harness going to the dash.. Yeah, list all 10. NOT the engine harness colors, those are easy.

 

[84EdH]

Re: Wiring problem on 350 mag Mercruiser Thunderbolt 4 (module on distributor)

I am not at my boat right now. However, I have a "parts" boat of the same year with a 350 engine. So, the parts boat has a voltmeter. I think my boat does also. There are 7 wires on the boat side cannon plug.

orange
green
white
brown
a heavier slightly less brown
yellow with red stripe
a heavier red

 

[Don S]

Re: Wiring problem on 350 mag Mercruiser Thunderbolt 4 (module on distributor)

Oh wonderful, you have a couple missing from the harness.
Your best be would be to pull out the old wiring harness, get a new harness to go from the engine to the instruments and wire it in.
Your harness plugs aren't going to work, color codes are different.
Below is the wiring diagram of how your instruments should be wired for the newer engine harness. You can retag wires, trace them out and re-use them if you want. But it's going to take some work re-wiring. everything (and finding those missing wires. they appear to be the main positive and ground.)

View attachment #10 GM 4 Cyl 85-89 214.pdf

 

[Don S]

Re: Wiring problem on 350 mag Mercruiser Thunderbolt 4 (module on distributor)

However, I have a "parts" boat of the same year with a 350 engine.

Missed that on my last post.

Use the harness and instruments from the parts boat. Don't even try to rewire the old.

 

[84EdH]

Re: Wiring problem on 350 mag Mercruiser Thunderbolt 4 (module on distributor)

The parts boat is a 1979. Sorry for the confustion. I wont know until I get with my actual boat to know for sure if the instruements and wiring are the same as the 1979 parts boat I am referencing.

FYI I did a continuity test on this boat side cannon plug. The heavy red wire connects to both #4 and #6 prong. #2 white #3 green. #5 Brown #7 yellow #8 orange. #1 heavy grey with a thin, faded red stripe (instead of my earlier descript of lighter brown. go figure fading over 33 years) also, the #10 has no prong..it is just blank with the number stamped where it would go.

does this change anything?

 

[84EdH]

Re: Wiring problem on 350 mag Mercruiser Thunderbolt 4 (module on distributor)

Don, I am wondering if the fact that the red wire accounts for two pins and the #1 wire being a heavier gray wire with parts of a red stripe might change my need for a boat side wiring harness?

Or am I just wishing on a star?

thanks, Ed

 

[84EdH]

Re: Wiring problem on 350 mag Mercruiser Thunderbolt 4 (module on distributor)

New info. on my wiring issue. The old 9pin cannon plug uses #1 as ground. most of the other pin positions correspond to the new 10 pin positions, if you convert the old color codes to the new. Can I just hook up the old boat harness (through new 10 pin boat side plug + pigtails to the newer engine 10pin plug?

I have to make some provision for two wires not accounted for on the newer engine: first the audio buzzer wire...thats easy, just add the buzzer. the other wire is on the middle pin, a brown/white. for the trim sender. I dont think my trim sender wire went through the cannon plug on the old harness.......anyone familiar with this?
thanks, Ed