Ignition switch test ?

McL0V3N1121

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I believe my ignition switch is bad. I have a Multi Meter to test it, I've never really used a multi meter but I went a bought a decent one. How can I test my ignition switch to find out if it is bad? Also how can I test my ignition coil to tell if it is bad ? My overall problem is that I'm not getting spark to the plugs. But I still want to test my switch and the coil. It is a 120 Mercruiser on a 1966 sterncraft. I believe the motor is original with this boat. Gm block 4 cyl
 

Bt Doctur

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at the ign switch should be a red wire(12v) on the "B" terminal, The "I" terminal(purple) should be 12v when switched to "on", the "S" terminal (yellow/ w red stripe)should have 12v when turned to "start" position.
With the key "on" should see voltage at the + side of the coil
 
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Really nice thing to have a DMM that is.... Invaluable tool...

You can check the switch for power at the various terminals on the back side.

B" terminal should have power at all times coming from the battery.

"I" terminal gets powered when the switch is in the run position, and

"S" gets powered when the switch is in the start position.

test by having the black wire on a good known ground, and the red wire on the terminal you want to test. switch on the meter should be on Volts DC

From DonS sticky at the beginning of the forum:
http://forums.iboats.com/forum/engi...hooting-your-engines-starting-system?t=167035


You test the coil by setting the meter to OHMS and checking resistance on the primary and secondary winding in the coil... and compare it to what the manual says it should be between.



You can also test spark plugs with it:

 

McL0V3N1121

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The ignition switch that I have had 4 ports for wires on the back of it. 3 in a circular shape around it and 1 that sticks out but is in the center. The 3 ports say ign, acc and bat. And I assume the 1 in the middle that's not labeled is the ground. I do not have a purple wire in my engine wiring harness.
 
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The ignition switch that I have had 4 ports for wires on the back of it. 3 in a circular shape around it and 1 that sticks out but is in the center. The 3 ports say ign, acc and bat. And I assume the 1 in the middle that's not labeled is the ground. I do not have a purple wire in my engine wiring harness.


There is no ground on the switch unless it has a light on it to see it at night...

You need a terminal to "start" the engine, it's not bat, ign, or acc.... I'd check the middle for your "S" terminal.
 

McL0V3N1121

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That would make sense. I will check that when I get home. Thanks. And to check the ignition coil I should simply check to see if I get 12V on the + side ?
 
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are you running points or has it been converted to electronic? it matters for the voltage on the (+) on the coil..

coil resistance test video... sorry a little drawn out...

 
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McL0V3N1121

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Ok so I tested my ignition coil and it tested good on both the primary coil ( the "-" & "+" ) top connectors and the secondary coil ( inside ). But mine is leaking oil out of the top where the main wire goes from the coil to the distributer and that is stopping it from passing power. So I need a new ignition coil. This was an amazing video you showed me and it helps me so much. Thank you a million +1.
 
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Ok so I tested my ignition coil and it tested good on both the primary coil ( the "-" & "+" ) top connectors and the secondary coil ( inside ). But mine is leaking oil out of the top where the main wire goes from the coil to the distributer and that is stopping it from passing power. So I need a new ignition coil. This was an amazing video you showed me and it helps me so much. Thank you a million +1.


At 3:10 of that video he talks about two wires on the (+) on the coil. you should have the same thing (With Points still) . One wire gives power to the coil from the starter solenoid when cranking.. full 12-volts and a 2nd resistance wire that gives the coil (reduced) power with the key in the run position. the voltage will be less like 7 to 10 volts to save the points from burning up. The negative terminal on the coil has 3-wires... One goes to the distributor, one to the shift interruptor switch which momentarily kills spark to help in shifting into neutral from gear while in the water (only) not on land and not from neutral into gear, and a 3rd wire to your tachometer at the dash to show RPMs..

You know how many people buy new coils and change them without testing them first
..
Nice to have a multi meter :thumb:
 
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McL0V3N1121

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This is really helping me. I have a question that's driving me crazy. When I got this boat the wiring was all out of wack, 1 long wire run was actually 5 wires pieced together to make 1 long wire, open wires touching just rats nest everything. So I cut out all the wires that obviously weren't right and am trying to hook everything up correctly with good wires and new ends, cleaning all connections with wire brushes all the good stuff. I honestly think I have wires missing and routed wrong. I have the manual but there's 2 engin wiring diagrams that says its for my engine and am not sure which one to go by. Is there a way I can tell where every wire ( from gauges to the engine, tilt n trim, hydraulic pump etc...) goes correctly ? But I do know the coil is bad and that's a big help. I believe most of the wires are hooked up correctly but would just like more clarification. If possible.
 
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What manual are you using now? If possible try are use the correct colors for the new wires, will make troubleshooting later much easier. With a '66 you should be using Service Manual #1 which will cover your engine and drive.

this is the Mercruiser factory repair manual not aftermarket:
http://boatinfo.no/lib/mercruiser/ma...uiser1.html#/0

here is the page that covers wiring diagram for your engine. There are two. It looks like it depends on which voltage regulator you have. Back then there were external of the alternator, now they are built in. It's also possible you have a newer alternator with the VR built in so that would alter the wiring a bit.

http://boatinfo.no/lib/mercruiser/ma...ser1.html#/282

We use to be able to download the manual but they (Mercruiser) put a stop to it... something about copyright...... but you can scroll thru these and print pages you'd like. Ebay has them if you keep your eyes on the look out.
 
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McL0V3N1121

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this is the manual I have, paid $7 to download it. how can I tell which voltage regulator I have ? my alternator looks like it may still be original. also, in this manual further down it shows another engine wiring diagram for my engine that says serial # 3770650 and up. mine is 66+. on page 3e-31, would this not be for mine ?
 

McL0V3N1121

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i have the transistor regulator. i found the transistor regulator laying in the boat, it looks old, but may still be good. how can i test it to find out if i need to replace it or not ?
 

Scott Danforth

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Ok so I tested my ignition coil and it tested good on both the primary coil ( the "-" & "+" ) top connectors and the secondary coil ( inside ). But mine is leaking oil out of the top where the main wire goes from the coil to the distributer and that is stopping it from passing power. So I need a new ignition coil. This was an amazing video you showed me and it helps me so much. Thank you a million +1.

If you have oil leaking from the coil, it is time to replace it.
 
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