Help with Merc 5.7 wiring

johnebquick · 06-22-2009, 10:33 PM

I'm new to boats and I'm trying to do a lot of maintenance and upgrades myself. It's tough when info is limited but It's a challenge and after it's done and fixed, It's satisifing. Well I'm definitely not at that stage yet. LOL

Does anyone have a good diagram of the merc 5.7L wiring? I have found a few and I'm trying to wade through this and fix my problem.

Background....

When I purchased the boat last season, I knew it needed some work to get it up to speed. In the most part everything worked and I am in the stage of upgrading now. I fabbed a new aluminum dash and remounted all gauges, did a total rewire of the motor and accessories, and upgraded to an auto flat fuse system instead of the barrel fuses. It took some time but I'm almost finished. I have now rewired something wrong and can't figure out where I went wrong. I had no problems starting and running the motor before the wire "upgrade" but now it won't start. I will crank but not catch and run. I am getting spark from the cap, and fuel when I manually pump the throttle but I think I'm not getting fuel to run? Please throw out some suggestions on where to start to look and possible solutions.

John

fishfighter · 06-23-2009, 01:13 AM

Need a little more info on your engine. Is it carbed,MPI ? What year,prevortec or not? Are you running a tb ign system?

johnebquick · 06-23-2009, 03:40 PM

1979 SeaRay 24ft SRV Cuddy
1979 Mercruiser 5.7L
4 brl carb
alpha 1 - Gen 1 Outdrive
Not sure about the pre-vortec
As far as I know non TB Ignition
4 Pin Key switch

nautiduck · 06-23-2009, 06:05 PM

You have spark at the cap, what about at the plugs? Are you still running points or do have electronic ignition. First thing to check do you have the spark plug wires running to the right plug? With a '79 350 your definately pre vortec that didnt come into play until '96. I have no clue what a TB ignition system is, I saw TB and thought throttle body injection but at that age and the fact is that you have a carb, so thats not it. Im guessing you have a Rochester carb? During upgrades did you change anything on your engine? Plugs, wires, points, coil? If you still have points check the gap, check all the wires going to the coil making sure the polaritys right. Dribble a little gas into the top of the carb and crank it over if it fires, its probably fuel if it still doesnt its most likely spark. I will see if I still have my service manual for that era mercruiser engines and outdrives. If so I will scan in the wiring diagrams and send them to you. I had an '82 Chris Craft with the 350, I think its identical to the '79 the outdrive may be slightly different but the engines the same.

johnebquick · 06-23-2009, 07:39 PM

OK, I went out and cleaned up and did some re-routing of the wires and labeled them. It ran two weeks ago when I last ran it with no problems. I touched nothing at the engine side of things. I probably missed or wired something wrong.

After doing some investigating, this is what I found....

Plug 1 / 8-pin
____________________________________
1) Black-------------------Ground
2) Blue--------------------Cuddy cabin lights
3) Brown/white-stripe---Step Down Pump
4) White------------------Stern Running Lights
5) Brown------------------Auto/bilge pump
6) Yellow------------------Blower at Motor
7) Brown------------------Run/Bilge pump
8) Black-------------------Ground

Plug 2 / 6-pin
______________________________________
1) White------------------Port run light
2) White------------------Stb run light
3) Orange/blue-stripe---Horn
4) Grey/Red-stripe-------Bow run light
5) Black-------------------Ground
6) Black-------------------Ground

Main wire Harness
______________________________________
1) Black-------------------Ground
2) Brown------------------Sender to Tach to tach
3) Green------------------Sender to Water Temp
4) Red/White-stripe-----Sender to Amp Meter
5) White------------------12V to Key-switch Acc/Run
6) Red---------------------Constant 12V
7) Yellow------------------12V to solenoid when starting
Goes through Neutral interlock switch in your control.
8) Orange------------------Sender for Oil Pressure
10) Purple------------------Sender for Trim/Tilt

I have wired all Nav Lights in the gauges in with the running/nav lights to a separate switch.

*****I seem to have found the Problem!!!*****
I found 2 wires not hooked up. 1black and 1white wire going to the shifter control. Not sure what this is????? The Neutral interlock worked when this was not powered up. I'm assuming that black is ground and white would be either Accessory power or constant power. I'm guessing accessory power.

Yellow out of the harness to white and black is back to the yellow hooked up to accessory power ?

Help,
John

sf_surfr · 06-23-2009, 07:54 PM

Try this bro.

johnebquick · 06-23-2009, 08:21 PM

This is what I found......

See attachment.....

06-23-2009, 07:39 PM	#5
johnebquick Anthony's Ark is a blowboater Join Date: Jul 2006 Location: Bear, DE 19701 Posts: 285 Credits: 6,818.4 Boat: 1979 Sea Ray Cuddy Home Port: Delaware City, DE Best Catch: 55lb striper / Sea Isle NJ Occupation: Maintenance Director / Gateway Foundation	OK, I went out and cleaned up and did some re-routing of the wires and labeled them. It ran two weeks ago when I last ran it with no problems. I touched nothing at the engine side of things. I probably missed or wired something wrong. After doing some investigating, this is what I found.... Plug 1 / 8-pin ____________________________________ 1) Black-------------------Ground 2) Blue--------------------Cuddy cabin lights 3) Brown/white-stripe---Step Down Pump 4) White------------------Stern Running Lights 5) Brown------------------Auto/bilge pump 6) Yellow------------------Blower at Motor 7) Brown------------------Run/Bilge pump 8) Black-------------------Ground Plug 2 / 6-pin ______________________________________ 1) White------------------Port run light 2) White------------------Stb run light 3) Orange/blue-stripe---Horn 4) Grey/Red-stripe-------Bow run light 5) Black-------------------Ground 6) Black-------------------Ground Main wire Harness ______________________________________ 1) Black-------------------Ground 2) Brown------------------Sender to Tach to tach 3) Green------------------Sender to Water Temp 4) Red/White-stripe-----Sender to Amp Meter 5) White------------------12V to Key-switch Acc/Run 6) Red---------------------Constant 12V 7) Yellow------------------12V to solenoid when starting Goes through Neutral interlock switch in your control. 8) Orange------------------Sender for Oil Pressure 10) Purple------------------Sender for Trim/Tilt I have wired all Nav Lights in the gauges in with the running/nav lights to a separate switch. ***I seem to have found the Problem!!!*** I found 2 wires not hooked up. 1black and 1white wire going to the shifter control. Not sure what this is????? The Neutral interlock worked when this was not powered up. I'm assuming that black is ground and white would be either Accessory power or constant power. I'm guessing accessory power. Yellow out of the harness to white and black is back to the yellow hooked up to accessory power ? Help, John Last edited by johnebquick; 06-23-2009 at 07:41 PM.

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06-23-2009, 01:13 AM	#2
fishfighter Bite me Join Date: Dec 2007 Location: Gulf of Mexico Posts: 222 Credits: 1,665.4	Need a little more info on your engine. Is it carbed,MPI ? What year,prevortec or not? Are you running a tb ign system?

06-23-2009, 03:40 PM	#3
johnebquick Anthony's Ark is a blowboater Join Date: Jul 2006 Location: Bear, DE 19701 Posts: 285 Credits: 6,818.4 Boat: 1979 Sea Ray Cuddy Home Port: Delaware City, DE Best Catch: 55lb striper / Sea Isle NJ Occupation: Maintenance Director / Gateway Foundation	1979 SeaRay 24ft SRV Cuddy 1979 Mercruiser 5.7L 4 brl carb alpha 1 - Gen 1 Outdrive Not sure about the pre-vortec As far as I know non TB Ignition 4 Pin Key switch

06-23-2009, 06:05 PM	#4
nautiduck I think Admin is going to let me have this space Join Date: Apr 2008 Location: Rock Hill SC (Charlotte) Posts: 1,272 Credits: 3,847.3 Best Catch: Duckie	You have spark at the cap, what about at the plugs? Are you still running points or do have electronic ignition. First thing to check do you have the spark plug wires running to the right plug? With a '79 350 your definately pre vortec that didnt come into play until '96. I have no clue what a TB ignition system is, I saw TB and thought throttle body injection but at that age and the fact is that you have a carb, so thats not it. Im guessing you have a Rochester carb? During upgrades did you change anything on your engine? Plugs, wires, points, coil? If you still have points check the gap, check all the wires going to the coil making sure the polaritys right. Dribble a little gas into the top of the carb and crank it over if it fires, its probably fuel if it still doesnt its most likely spark. I will see if I still have my service manual for that era mercruiser engines and outdrives. If so I will scan in the wiring diagrams and send them to you. I had an '82 Chris Craft with the 350, I think its identical to the '79 the outdrive may be slightly different but the engines the same.