96 Thunderbolt V no Voltage at coil?

subysti · Jun 22, 2013

OK I've looked at the troubleshooting and wiring diagrams. The positive purple wire goes in to a round plug pin #5. Where does it get it 12volts from? At least I'm glad I know why its not starting I just want to make sure I find the problem to fix it.

Boat is a 96 Larson with 5.7 merc thunderbolt V

Bondo · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Ayuh,... The ignition circuit is powered from the keyswitch,...

Don S · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Power from the key switch I terminal (purple wire) also goes through your lanyard kill switch if you have one.

subysti · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Well checked voltage from keyswitch all the way back to round plug. 12 volts the whole way. I think I have a dead short in the coil because I removed the supply wires and 12 volts came back. I have another coil I'm going to try if I can get the old one out, the bracket and bolt are rusted beyond recognition.

Don S · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Disconnect the wires from the - terminal on the coil before you buy a new coil.

subysti · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

that's the same print I have. Found the problem is a bad ground it seems. I connect to positive at coil and another ground point and I get 12 volts. Can I run a wire from battery for ground or is that not a good idea?

Bondo · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

subysti said:
that's the same print I have. Found the problem is a bad ground it seems. I connect to positive at coil and another ground point and I get 12 volts. Can I run a wire from battery for ground or is that not a good idea?

Ayuh,... It would be better to clean, 'n fix the existin' grounds,...

Where, exactly aren't you getting Ground,..??

subysti · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Ok. I'm completely befuddled at this point. I measure at the + side (purple wire) and - side (2 grey wires) of the coil and get nothing. I connect to the positive side of the coil and use another ground point on the engine and i get 12 volts. I remove the wires from The coil and measure the wires and get 12 volts. I reconnect the purple wire to the coil and measure from the coil to either of the grey wires and I get 12 volts. I only lose the 12 volts when I reconnect the grey wires.

Oh and this is with a new coil installed.

subysti · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Ok I've tried with either grey wire connected and I still lose the 12 volts. I also measured 1 ohm on the primary and 10K ohms on the secondary. Anyone have the specs for this coil? Coil i put in is a Sierra 18-5438.

Don S · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

I measure at the + side (purple wire) and - side (2 grey wires) of the coil and get nothing.

Assuming you are using your meter with one lead on the + and the other lead on the - coil terminal, 0 is what you should get. That is a voltage drop test. For the tests you need to be doing, you need the black lead on a good clean engine ground or even the black battery cable on the battery. Now you will be doing voltage tests.

subysti · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Aaarrrrgggggg. Ok if I check that way I get 12 volts. I thought I had to check on either side of the coil. So I only use the + side of coil and then to battery ?

Don S · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Voltage tests are always done with the black test meter lead to ground.

I would disconnect the gray wire on the back of your tach just to make sure it's not shorted to ground.

subysti · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Well went through the rest of the chart and go no spark anywhere. Going to go buy a cheap generic coil tomorrow at a car place just to confirm I didn't get a new bad coil. Otherwise I have to order a $500 ignition module.

Don S · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Did you take the gray wire off the tach? Not off the coil, off the tach.

subysti · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Not off the tach. I assumed if I was getting the 12 volts at the coil then it wasn't shorted. The flowchart didn't say to do that but I will listen to the voice of experience and try that. Anything to not have to buy a new icm. Why is there a wire from the coil to the tach anyways?

Don S · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Do the tests, as stated, all of them until you run into a specific point that something fails. Then you will know what the problem is.

Sounds like all you want to do is change parts.

Fun Times · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

subysti said:
I measure at the + side (purple wire) and - side (2 grey wires) of the coil and get nothing. I connect to the positive side of the coil and use another ground point on the engine and i get 12 volts. I remove the wires from the coil and measure the wires and get 12 volts. I reconnect the purple wire to the coil and measure from the coil to either of the grey wires and I get 12 volts. I only lose the 12 volts when I reconnect the grey wires.

subysti said:
I thought I had to check on either side of the coil. So I only use the + side of coil and then to battery ?

The - on the "coil" is not actually the same as an engine ground.

If you're not getting a good spark, check for approximately 12+ VDC from the coil positive terminal (purple wire) to engine/battery ground with the ignition switch in the ON position. You should also get approximately 12+ VDC from the coil negative terminal (Grey wire) to ground.

subysti said:
Why is there a wire from the coil to the tach anyways?

The grey wire between the tachometer and the - side of the coil is used as the signal wire to operate the tachometer. (AKA, The coil is the sensor for the tachometer).

subysti · Jun 22, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Thanks for the info Fun Times. Don S, I dont want to just throw parts at it. The coil was a planned replacement anyways. I went through the troubleshooting flowchart and after doing all the checks it came down to replace the ICM. I dont want do do this if I dont have to. The very first step was to check the wiring at the tach but not remove it and check for spark so I didn't know to try that. Now that you suggested it I will try it tomorrow when the sun is back out. Thanks for all the info.

sptjet90Reflexx · Jun 23, 2013

Re: 96 Thunderbolt V no Voltage at coil?

I was having the same problem with my thunderbolt IV system on my 4.3l merc. Turns out I solved the WHOLE issue buy making a new ground on my engine. If you follow your ground cable from your battery, You should see probably 3 wires, 1 is the main lead from the battery, the other is a ground for your trim pump and 1 more is possibly going to a distribution block which is what your ignition system is connected to. I cut the grounds off and ran them to a new bolt on the motor. My engine started up like it never had a problem. According to my flow chart I also had to replace my Ignition amplifier or ICM I guess some people call it. Ground solved it.

subysti · Jun 23, 2013

Re: 96 Thunderbolt V no Voltage at coil?

Well I disconnected the grey wire from the back of the tach, that was harder to get to than anything else. Still no spark. Double checked my spark tester on a car to make sure it was good

96 Thunderbolt V no Voltage at coil?

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