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1990 Mercruiser straight inboard wiring

S

Sjohansen

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Looking for a wiring diagram. I have what I believe to be a 90ish mercruiser 5.7 inboard with a velvet drive. It has a 8pin square/flat wiring harness at the motor and back to the helm. Anytime I look for wiring diagrams all I get is the round 9 pin harness so I’m having trouble identifying what I have. Looking for any insight on this style wiring harness.
 
if the plug is rectangular, does it use one of the 'pins' as the 'key', to ensure the correct orientation before mating the halves?

If so, is the 'key' used for the thicker BLACK wire?
 
Can you supply more info.
Is this EFI, TBI, or carbed?

Do you know what distributor is there? Is it a Thunderbolt or different one?

As much info as possible like engine serial number???????
 
Here what I found doing a google search. The pin out on rectangle is based on color of wire and size and should be the same as the pin out of the round cable (use colors on rectangle and match to colors on round as labeled in schematic in image). Can be rectangle on both ends or round to rectangle based on what is wanted/needed.

8 pin rectangle connector.jpg
 
looks like a vortec SBC...I'd guess with a mallory distributor and a rear mounted heat exchanger...the pic attached doesn't "zoom in" much before going grainy...

The connector shown looks like the ones Crusader uses... being as there wasn't much detail to go on, my best guess is somewhere in the previous life, an engine swap occurred...
 
It looks to me that this boat did not come with a Mercruiser originally.
As Mark suggested, this may have been equipped with a crusader originally.

Mercruisers are ALL Black including the carb.

This engine has,
Blue carb
Silver intake
Block, Manifolds and heat exchanger/cooling looks to be all black.

Also note the Ballast resister. This means that this is a Point ignition. Merc went to electronic in the early 80's and based on that engine it is a 87 or newer and by then merc ignitions were all electronic. (center hole valve covers which also means One piece rear main seal transitioned in late 86 and fully in 87).

5233.jpg
 
In addition to Jack's observations, I'll add the alternator appears to have Blue paint as well...so the theory of a Crusader being OEM in the hull is very likely...I'll also add that the wiring appears to need some attention as well...and the cooling system's plumbing....and the ventilation system....not to mention the other side...
 
Thanks all, So I will post some additional photos from my phone. So seems like I got a Zombie motor! Bought the boat mostly for the hull but I was told by the owner that it had a new block "crate motor" with no hours on it so I wondered if I could clean it up and run it for a year or two before repowering. The motor starts, cooling system moves water however multiple leaks that need to be addressed. Carb gasket is leaking air so its got a high pitch air leak. RPM gauge on the dash does not register. When looking over the wiring I found multiple wires that are not landed anywhere on the engine side (i assume one of which would be the sending wire for the tach). That is why I was originally looking for some wire diagrams. I am debating whether I should pull the motor or not. It would give me opportunity to redo the engine compartment and pull/clean the gas tanks, replumb etc. Would like to run it for a year to see how this HP performs etc.

The carb is a blue quadrajet
The ID plate is gone from the block
The block is stamped GM 5.7LG SGI, Also has 12040 stamped

Wires are quite faded so its kinda hard to make out the original colors.

Thank you to all that have chimed it!!
 
Can you find the main electrical connector that all those wires come from? Is it a Large round connector?

If it is, the wiring and colors are standard.
if its a large round with 8-9 pins/sockets.
You can purchase just the engine side new. Then follow a schematic which we can provide with colors and connection locations.
 
kghost said:
Can you find the main electrical connector that all those wires come from? Is it a Large round connector?

If it is, the wiring and colors are standard.
if its a large round with 8-9 pins/sockets.
You can purchase just the engine side new. Then follow a schematic which we can provide with colors and connection locations.
Click to expand...
 

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OK enough of the short answers. This is getting frustrating.

In that picture you used to answer my question, That is the MALE side.

1. We will call wire harness from helm to engine Harness A
2. We will call wire harness ON engine Harness B

Which harness does that MALE connector belong to? A or B
 
this is the factory crusader diagram at the engine...with the various connector options...the oddball is the warning system wires - not all engines came with them...

there may have been some butchering done around the circuit breaker and slave solenoids...haven't seen enough detail in the pics to tell...
 

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If you wish to replace the engine wire harness B

Here is a link to a harness with both MALE and FEMALE ends. You can plug the correct one in and cut the other end off and then rewire the engine.

I would recommend leaving 8-10 inches more wire length at each connection then is needed when you cut to attach to the point of connection. That way the harness will not be to tight or short.

bpi.ebasicpower.com

Wire Harness Square Male to Square Female 8 Pin 4 Feet Marine Color Coded [MAR6117-04] - $42.95 : ebasicpower.com, Marine Engine Parts | Fishing Tackle | Basic Power Industries

ebasicpower.com Wire Harness Square Male to Square Female 8 Pin 4 Feet Marine Color Coded [MAR6117-04] - Wiring Harness, 8-prong male rectangular plug male/female, 4'. Red/Black wires - 10 Gauge all other wires - 16 Gauge Note: This wiring
bpi.ebasicpower.com
 
This is nightmare fuel for sure, at least for me. I'd be pulling out ALL that funky wiring and installing new harnesses. I don't want any fires or other surprises on my boating excursions! To the OP: boats are like aircraft in that once you leave the safety of the dock, you're at the mercy of your equipment. NOT having that gear in top condition risks your life and safety and those with and around you. Getting stranded and calling SeaTow may sound like a good safety plan, but those people go to the same risk as you when they come to haul you back home. So please, get the wiring, plumbing and fueling sorted out. If it means paying someone to do it properly, then do. We all want it so that when you turn the key the boat doesn't go BOOM and blow you to atoms, and everyone enjoys a safe and reliable outing.
 
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