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Mercruiser 502 EFI Harness

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"A+B are the terminals on

"A+B are the terminals on top of the slave solenoid. A is red B is yel/red. I have a circuit breaker on the starter, which has 2 wires red/pur and ORNgoes to alt), The top breaker, in the box with solenoid aka slave 50A has 3 wires, red, red/pur and red.

the problem remains- no juice to the bottom harness. Nada, no gauges, no power going to top breaker, no fuel pump prime just quiet when turning the key on or start

When I bypass the starter breaker, everything works except the key start. But, I have a new starter breaker, which replaced the old breaker that was ok, but had the same problem.

When I jump A+B on the slave solenoid it fires right up.

I just went out and buttoned the dash back together. The heavy red that goes to the dash panel doesn't go through the harness. Battery>starter>front harness"
 
"No juice to the bottom harnes

"No juice to the bottom harness and no fuel pump prime with key=START and no starter spinning all mean no current flowing thru the RED/PUR wire from the 50A circuit breaker.

Does what you call the starter breaker have a reset button? If not, it is most likely a 90A slo-blo FUSE.

You say when the "starter breaker" is bypassed, everything works but the "keystart" - reaffirms conclusion in first paragraph and begs the question: How are the wires connected on the 50A circuit breaker - the three wires?

If you have to bypass tthe new "starter breaker", then sommething isn't making a good electrical connection. Check it to make sure it will pass several amps and then verify the connections are clean and tight. Use a stainless wire brush on the wire end lugs if available."
 
"Mako, spoke to Mark and it se

"Mako, spoke to Mark and it seems the 90A may be connected to the wrong lug on the solenoid. Checking it tomorrow and will give a update on the repair."
 
"thanks- The breaker was on th

"thanks- The breaker was on the correct solenoid post. I pulled it, I tested it and it was open. I just took it off and connected the wires directly to the main post on the starter solenoid.

After bypassing the 90A circuit breaker solenoid fuse located on the starter:

Key On - one beep alarm, gauges work, fuel pump primes.
Key Start- nothing. not a click, however, I see a slight movement (current draw) in the gauges in "Key Start"


It starts no problem if I jump between terminals A + B on the slave solenoid.

I don't have a helper to turn the "key Start" while I probe.

On page 4A3 in Service Manual 16, shows a testing "continuity" procedure for the slave solenoid, it jumps 12v to yellow red wire on the lower terminal. then has the meter on posts A+B to look for movement.

Should the Slave Solenoid be eliminated on the list of suspects? Or does this mean the slave is bad?"
 
fyi. My batteries were new in

fyi. My batteries were new in July. I don't have a "battery tester" they are showing 12.5 for number 1and 12.55 for number 2. The motor turns over fine when A+B are jumped. I consider A post on the Slave to be the RED wire and the B post to be the YEL/RED. With Key On the RED gives me 12.5. I also have shore power and an inverter. These readings are with the inverter turned off. When the motor is running I'm getting 13-14v
 
"Zero:

W/the key in the run

"Zero:

W/the key in the run position the slave should have 12 vdc on one of the top studs. W/the shifter in neutral, turn the key to start to see if the small yel/red wire gets 12 vdc. If the volts are there and she won't turn over then try jumping the big studs on top to see if the starter engage. If it does; change the slave."
 
"Good to hear you are mamking

"Good to hear you are mamking progress.

For the starter mounted solenoid, the conventional nomenclature is to label the battery post (large one) B or BAT, and the small engagement terminal (yel/red wire) S. The other small terminal used to be I to feed the ignition but now, if used, is normally to feed the fuel pump during cranking. If you are jumping (A+B) at the slave solenoid, sounds like its bad and you can ignore the rest. If you are jumping at the starter solenoid, red on

I'd encourage you to NOT remove the slave solenoid. The starter solenoid draws considerable current and the yel/red wire in the harness is too small to handle it in most installations.

To verify the slave solenoid is the issue, remove the yel/red wire, at the starter solenoid, and hook up the test light between ground and the wire you removed. It should light with the key = START. You should also hear the slave solenoid click. Make sure the light is as bright as when hooked to the battery. Sometimes the contacts in the slave solenoid will burn and pass an amp of current but not much more."
 
"Hi Mako. the A and B termin

"Hi Mako. the A and B terminals I was referring to are on the slave solenoid, on top the motor.

I just pulled the slave solenoid to bench test.
I get a click.

next, tracing the yel/red's one goes to the harness is the one you're talking about. The other goes to the solenoid, which I'm sure is good due to jumping A and B"
 
"The slave clicking is good bu

"The slave clicking is good but you need to make sure it will pass the current from A to B. If that's ok, the slave is ok and you need to check the Yel/Red, from the key back to the slave.

The only thing in that path should be the Neutral safety switch(NSS). It is usually in the control box. If the key has +12 on the Yel/red lug when key=START (think you said yes to this earlier), then check for +12V at the slave solenoid lug of the yel/red wire. If that is ok, the NSS is ok. If not, hold the key to START and move the control around the Neutral position. If that doesn't get +12 to the slave, you'll have to check in andn around the control box. Again, yel/red wires carry the starting current.

The other thing to check is the ground on the slave solenoid. Some have common grounds and some have isolated grounds. Hook the test light up too ground and probe the black wire on the slave with key=START. If the light comes on, the ground connection is bad, light should stay off. If the ground wire is bad, sometimes the test light will provide an alternate path and the starter circuit will work - until you remove the light. In that case, clean/renew the ground wire for the slave."
 
Zero:

Buy a new one; they a

Zero:

Buy a new one; they are cheap. Open the old one and look at the chincy contactor used; it burns the surface until the resistance is too high for good current flow. A good indicator for replacement is one of the studs will darken. To me it is a "keep a spare on board" part or a replace as part of a 5 year PM.
 
"Thanks again a new slave this

"Thanks again a new slave this week. The old one didn't look so old. Bright and shiney. I put the old one back on and tested the small yel/red from the lower slave terminal, no juice at Key Start. Also used a light to test the key side of the yel/red. There was no juice going to it, Therefore no "click".

I kept a Fuel Injected vette harness that I had extra. It gives me something to scarf off of, ie 30A jumper and long lead for a test light so I can hang it, look back at it while I turn the key.

Used my jumper across A+B it still starts that way, no problem.

The issue is clearly Key Start position, no juice.


Now to check the key back to slave-

I have juice to the panel, and with bypassing the 90A starter breaker fuse, I get
juice with Key On, but no juice to Key Start.

I don't have juice to key start, NSS could be a fault, but I won't know until I get 12v at Key Start first?"
 
"Sounds like you have the rest

"Sounds like you have the rest of the plan in hand.

You can test from the key back by jumping around the key. Key = ON and jump the B+, at the key, to the yel/red. If that turns over the engine, new key switch. Otherwise, on to the NSS. You can keep the jumper on while rocking the shift lever if needed.

Keep us posted."
 
"NAPA will have my slave solen

"NAPA will have my slave solenoid Weds 10/21. $23. such a deal. It'll be a nice day to install it too. Is there a secret easier way to disassemble/reassemble? Its located in a box with 2 relays, ign module, 50A breaker, cpu and mercathode. Of course, it's on the bottom and my fat fingers are barely long enough. you know what happens- nuts dropping down into the unknown."
 
"Nice day, took a few minutes

"Nice day, took a few minutes to look at the harness. With the old slave solenoid, I took a 10 gauge and jumped at the female end of the harness plug #6 red/pur to #7 yel/red and the motor turns, meaning the old slave is good and the yel/red lead on that part of the harness is good. I disconnected the coil at the dist. so it wouldn't fire. I gave 12V to the yel/red at the ign. and turned the key, nothing. Leads me to NSS."
 
You can bypass it under the da

You can bypass it under the dash or side panel w/a quick connector that just cuts the insulation.
 
"Guy, I bypassed NSS, and stil

"Guy, I bypassed NSS, and still have no juice in "key start" Then went back to the male plug on the harness and fed 12v to #7 which is yel/red and then used a test light on yel/red connection on the key ignition, and it lit up. Above, I fed 12v into #7 on male plug, and the engine turned over as normal. I'm thinking it's my connection at the harness plug, or my ignition. Should I jump yel/red around the plug?"
 
I haven't forgot you Zero;

I haven't forgot you Zero; been studying wiring schematics.

Starting over from the beginning:

Is there 12 vdc at the ignition switch B terminal?

Turn the key to run; is there 12 vdc on the I terminal?

Turn the key to START; is there 12 vdc to the yellow/red wire on the key switch and at the slave solenoid?

When the slave engages; is there 12 vdc to the starter solenoid?

The above have to be established to get the starter to engage.

Female receptacles on the engine barrell plug can become spread and loose over time. Inspect them carefully for spreading and corrosion; repair as needed. Probing w/i them can spread them more.
 
"I THINK I GOT IT, but after w

"I THINK I GOT IT, but after what I went through, my question still isn't answered-why I had a steady alarm, and why I shut down immediately on impact after a wave. After screwing with this thing since late summer. My Marina mechanic wanted to do the work, but he didn't communicate with me very well. He wanted $2k+ to replace lower starting/charging and upper MFI harness. He never pointed out to me what exactly the problem was, he said he doesn't work that way, and I would take it somewhere cheaper. I wound up bringing the boat home.

I have been looking at this female harness plug and it never dawned on me that it wasn't right.
Looks like it sucked off the collar from Male #7. The male side of the lower harness needs to be replaced, or I can bypass. The bypass would be ok if I needed the boat tomorrow. I am going to order a new male plug or harness. At the most, it's $250-$350.
Judges, take a look yourself, damaged from a hard wave, human being, or both? How about the repair? Just the barrels, plugs, or full harness? Or is there a way to fix this?


295422.jpg
male plug"">
295423.jpg
male plug"">
295424.jpg
female plug
 
"Zero:

Good work on finding

"Zero:

Good work on finding it. There is alot of corrosion on the other contactors. It can be cleaned w/a strip of fine emery cloth. Cut a 2"x1" strip and roll it up so it just fits in the hole. Twist the strip inside the connector. On the male plug I've used a woman's disposable nail file and cleaned the pins. If the rest of the wiring is good then just connect a jumper around it.

I bought a pigtail harness where the wires were all labeled and I cut them to length and crimped on the connector. The following company has what you need. http://www.ebasicpower.com/

Salt air did a number on the plug. A spray of WD-40 on the new/old plugs will help prevent corrosion. In fact, a spray on all the plugs can't hurt."
 
"I would bypass the connector

"I would bypass the connector using shrink connectors. Depending on the manufacturer, some connectors don't have leads in them if they're not used, notice #6. I didn't look at the schematic to see what this lead powers but don't be alarmed if it still doesn't work."
 
"Indeed, excellent job on find

"Indeed, excellent job on finding the root cause!

If you want to keep the quick disconnect, pigtails would be most economical. Like Rick suggested, use of adhesive lined shrink tubing is essential to a proper repair job, whether you keep the plug or eliminate it.

Though it doesn't answer the direct question, the modern electronics do not like poor, corroded, intermittent contacts. they do lots of wierd things when presented unstable signals. I'd check the switch warning loop wire (tan/blue tracer) and see if it makes contact with ground as you wiggle the harnesses around.

Also, go over the male harness connector and make sure it is ok else get one of those if you keep the connectors."
 
"I cleaned the terminals on th

"I cleaned the terminals on the plug and tapped in a direct line around the plug for #7 yel/red. Hello. I have "key start". I used shrink and neoprene, then a dress up black poly cover. If you didn't know what to look for, you would never notice it. I will replace the harness, once I have her winterized looking for storage- Indoors in central NJ.


295492.jpg
sr-1
 
"hey rick, after reading your

"hey rick, after reading your post a couple of times I think your looking at terminal #9 which doesn't have a lead. Thanks for the advice. I should have probed everything from the plug in the beginning instead of working around it. But at least I know everything else is good."
 
"Nice boat, what year. I have

"Nice boat, what year. I have a '95 I bought with a bad motor. Here it is after redoing the bilge, installing a new (to me) FWC 7.4. I used the 8.1 manifolds and elbows and updated everything to use the serpentine belt system. It worked out really well.

295502.jpg
"
 
"Hi Rick, that is beautiful!

"Hi Rick, that is beautiful! Love the stainless! The bilge looks brand spanking new! Where are the batteries?
Mine's a '93, the 502 merc is a '95. What is FWC?"
 
Fresh Water Cooled = FWC = ant

Fresh Water Cooled = FWC = antifreeze w/heat exchanger. Raw Water Cooled = RWC = lake/sea water runs thru engine.
 
"Batteries weren't in when

"Batteries weren't in when I took that pic. They are now in the back corners. There were still some wires to tie up too but she's finished now.

Can you keep a secret? That's not the $1,800.00 Gill exhaust system. That is the stock 8.1 Merc parts with the elbows stripped and polished. The new manifolds and the polished elbows cost me $700.00 which was not much more than the stock stuff and these will last forever (plus they're really shiny).

I had to fabricate a bracket to mount the electronics that used to bolt on to the old cast elbow.

I got a late start on it since I didn't buy it until May, then had to find a deal on all the parts, but I'm looking forward to a full summer of boating next year."
 
"yeah, mine's a stock cros

"yeah, mine's a stock cross ram mpi with the iron manifolds. They look ok after running about 150 hours on salt.

is the 8.1 merc a 500 or a 502? I can't tell if you have MPI or MFI. The 8.1 is 500 HP? and the headers are stock stainless? What is the boat?"
 
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