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View Full Version : Tach for Thunderbolt Ignition?


abbyrocket
04-04-2010, 02:52 PM
OK Merc people out there, I have a 1970 Merc 1150 that is now running on the Catalina. I removed the Airguide tach and speedo from the POS Tri-hull that I picked up last weekend, and installed them on the 8th grade woodshop quality panel of the Catalina. One small problem... there is a label on the inside framework of the motor that reads "Use only a Thunderbolt tachometer". Does anyone know if any damage will result from using the Airguide tack? I'd hate to fry the ignition box, since they cost about $375 to replace and I just installed a new stator. I'd hate to have to do that again just because I didn't follow directions! As for the stator... Check out the leads on my old one. My "parts" 1150 has the same problem. The wiring is rotted past the coils! Unrepairable! I found a replacement on ebay for $45.:D
Other than that, The Cat should be on the water by late this week. If all goes well, she'll make her GSG debut at Piru! :)

4998 4999 5000 5001 5002

JerrfyLube
04-04-2010, 03:26 PM
The Airguide tach you show is identical to the one i run on my '70 1350 ...should work just fine!

Bigfoot
04-04-2010, 03:37 PM
Im impressed with all your boating motivation lately. my merc has a green rotten wire comming out of the block too and I think thats why my tach maxes out to 6000 rpm when the ingition is engaged. I cant see any way to replace it but id like too.
Have you done any maitnence to that motor yeat??? Have you done a compression check??? Im just cerious because id love to learn how to work on motors and maintain them myself and repair them too.
I cant wait to see you float your boat.:D
Your wood work is fine and It looks like fresh paint, cool. way to go Phil....

GrumpyBobby
04-04-2010, 05:34 PM
Im impressed with all your boating motivation lately. my merc has a green rotten wire comming out of the block too and I think thats why my tach maxes out to 6000 rpm when the ingition is engaged. I cant see any way to replace it but id like too.
Have you done any maitnence to that motor yeat??? Have you done a compression check??? Im just cerious because id love to learn how to work on motors and maintain them myself and repair them too.
I cant wait to see you float your boat.:D
Your wood work is fine and It looks like fresh paint, cool. way to go Phil....

I have an airguide on mine, doesnt read correctly and not sure why but it hasnt caused any issues TIKO.

bf: Your tach is pegging because it's connected to the wrong wire. Mine did the same thing, if hooked up as per the instructions. I think it ended up being connected to the brown wire on the opposite side of the box. Will need to pull the cover and look, been a while.

abbyrocket
04-04-2010, 08:10 PM
The Airguide tach you show is identical to the one i run on my '70 1350 ...should work just fine!

You guys ROCK!
Ok, Jeff.
The big question now is "what do the leads connect to?". I'm thinking black to ground and green to one of the stator leads?

JerrfyLube
04-04-2010, 08:16 PM
Mine runs from the tach to the control box...there is a plug that attaches at the front of the box...from there im assuming it goes through the wiring harness and back to the motor....no idea on wire colors but ill poke around a little tomorrow on it and see what colors go to what.

abbyrocket
04-04-2010, 08:49 PM
Mine runs from the tach to the control box...there is a plug that attaches at the front of the box...from there im assuming it goes through the wiring harness and back to the motor....no idea on wire colors but ill poke around a little tomorrow on it and see what colors go to what.

I think that I know of the plug you speak of. The one at the front of the Mercontrol with the three slots in it? I never knew what that was for. I always used a spare wire in the loom to get the tach signal. I'm sure that it must connect to the ignition kill post on the switch. It would get the pulse signal until the key is turned to the off position and the circuit is shunted. How does that sound?

JerrfyLube
04-04-2010, 09:00 PM
I think that I know of the plug you speak of. The one at the front of the Mercontrol with the three slots in it? I never knew what that was for. I always used a spare wire in the loom to get the tach signal. I'm sure that it must connect to the ignition kill post on the switch. It would get the pulse signal until the key is turned to the off position and the circuit is shunted. How does that sound?

Thats the plug...i have no idea thats what it was for either till i knocked the plug loose while bouncing across some chop and my tach all of a sudden stopped working.

3 prongs although i have no idea if that means 3 wires going to the tach or not...never really paid attention to it. Thankfully, this motor has been 100% electrical trouble free so ive never really had to dive into it with a wiring diagram leading the way...so as far as what wires go where or what color they are, im just the blind leading the blind... :p Ill take a look at it tomorrow and tell ya what i find. Its all factory wiring so i should be able to give you the correct factory wire colors and where they all go. But your assessment of it sounds correct.

abbyrocket
04-04-2010, 09:15 PM
Unfortunately, the wires going to the plug were rotted beyond recognition, so I simply cut them. I removed the entire switch out of the Mercontrol box and dash mounted it. It will be an easy connection from there to the tach. I think I know which wires complete the ignition circuit. The previous owner jumpered them to bypass the rotted wiring in the switch. The first time I fired the motor, I couldnt get it to shut off. I grabbed my wire cutters and took a guess. Fortunately, I was right. Well, that's where I'll start, unless you see that it should go somewhere else.
Thanks, again, Jeff!

GrumpyBobby
04-04-2010, 09:17 PM
Thats the plug...i have no idea thats what it was for either till i knocked the plug loose while bouncing across some chop and my tach all of a sudden stopped working.

Reminds me of this weekend's Kat 750 run where the speedo took a dump at 142 and it was all I could do to recall the RPM vs speedo rules and just kept it tucked under 11,500 in 6th on the way back from LA LOL!

abbyrocket
04-04-2010, 09:48 PM
Reminds me of this weekend's Kat 750 run where the speedo took a dump at 142 and it was all I could do to recall the RPM vs speedo rules and just kept it tucked under 11,500 in 6th on the way back from LA LOL!

I hate it when that happens!:eek:

oldmariner
04-05-2010, 02:03 PM
On the subject of stators: mine had the same malady, so sent it to be rebuilt. Age had taken its toll on the insulation. Got it back today. Looks like a new one. I would predict that anyone with an older Merc probably has a similar problem. It may not show up until you are in the middle of the lake. I don't know if new ones are available, but there is a company in Alabama that does a great rebuild job. CDI Electronics, Inc. (256) 772-3829.
Address: 111 Commerce Circle, Madison, AL 35758.

abbyrocket
04-11-2010, 03:20 PM
Im impressed with all your boating motivation lately. my merc has a green rotten wire comming out of the block too and I think thats why my tach maxes out to 6000 rpm when the ingition is engaged. I cant see any way to replace it but id like too.
Have you done any maitnence to that motor yeat??? Have you done a compression check??? Im just cerious because id love to learn how to work on motors and maintain them myself and repair them too.
I cant wait to see you float your boat.:D
Your wood work is fine and It looks like fresh paint, cool. way to go Phil....

Mike,
I'm sorry, but I somehow missed your post, or I would have replied sooner.
Read my next post about the tach maxing out.
As for a replacement stator, check out Oldmariner's post on this thread. They are very resonablly priced, if you can't find a good used replacement. DO get it changed. I was told that if arcing occurs between the stator leads, it can damage the ignition box ($$$$).
The first thing I always do with a "new" engine is a compression check. You can find a compression check gauge online or at an auto parts store. Remove the #1 spark plug and screw in the fitting from the gauge. Let it crank for 3 or 4 revs and check the reading and compare to what is called for in the manual. Repeat for the remaining cylinders. If anything is wrong in the cylinders, now is the time to find out! If everything there is good, then I check the igniton. Remove a spark plug and pop it into the spark plug wire boot. Lay the plug against the head, and crank it over. You should be able to see spark across the gap of the plug. Repeat for all cylinders. If all is well and you see no other visual problems, pump some fuel into it and fire it up. Remember to use a water hose hookup at ALL times! Several seconds without water while running can ruin an impeller. Once it's running, do the smaller stuff. Rebuild the carbs, fuel pumps and a new water pump impeller. If all goes well, You could get these things done on a weekend afternoon. Those items are cheap insurance. Like was said before, don't trust the judgement of the previous owner. Now with all of that done, I usually go to cleaning and checking for loose connections or corroded wire. With all of these items taken care of, your engine should last many troublefree years. :)

Phil

abbyrocket
04-11-2010, 03:24 PM
Well, I tried to connect the old Airguide tach to the 1150 Merc today. I always got "all or nothing" to whatever I connected the leads to. If it registered anything at all, it was pegged! I'm waiting for a local outboard guru to call me back, but if anyone here has an idea, I open to suggestions.:confused:

Rod-B
04-11-2010, 04:07 PM
Well, I tried to connect the old Airguide tach to the 1150 Merc today. I always got "all or nothing" to whatever I connected the leads to. If it registered anything at all, it was pegged! I'm waiting for a local outboard guru to call me back, but if anyone here has an idea, I open to suggestions.:confused:

May or may not help. Merc section for tachs from a 1969 Airguide catalog. Might verify the tach is the correct model number. No wiring diagrams, I'm afraid.

Motorhead
04-11-2010, 05:25 PM
If you aren't opposed to having a modern tach on your boat the answer is very simple. Buy a tach that reads off the impulses of the stator. Most newer universal tachs read the AC sinewave from the stator. No ignition module woes to deal with. I wouldn't mess with the old meter and your motor again, as you could blow the pulse pack $$.

Keep in mind that the older tachs were installed for specific engine and ignition types. Some of these had modules that converted the ignition impulses & sent these to the meter. Other types had the modules inside the case. Add to all that, the electronic parts (diodes, resistors, capacitors, transistors) inside the tach case or module can be damaged by previous hook up attempts, or by age degredation

If you do some looking around, there are some nice retro looking tachometers that are being manufactured - they would look at home on a classic boat and they read the impulses from a 12 pole alternator - which is what you have.

abbyrocket
04-11-2010, 08:10 PM
Bruce and Rod...
Thank You both! I was hoping to use the old tach from the donor boat to save $. But you're right, if I damage the ignition module, that will cost much more than a modern tach. The chart will come in helpful if I decide to use the Airguide with an older motor. It's looking like the more modern Thunderbolt ignition won't agree with the Airguide at all.

JerrfyLube
04-11-2010, 09:27 PM
Phil, heres what i found out for ya...

On the face of my Airguide tach(looks just like yours) at the very top of the face there is a marking P-6487...i can faintly make out your numbers but they look the same so that tach will work for your motor if its functional. On the back there is a 3GA stenciled on in yellow paint. 2 black wires which appear to be factory, are spliced into the wires coming out of the tach.

Those two black wires run to the plug on the front of the control box. There is a third brownish\tan wire which i cant trace where it goes but im assuming back to the motor. The male part of the plug looks like this: = | One of the black wires goes to the top horizontal male connector and the other black wire goes to the vertical.

As far as i can tell, this is all factory original to this boat. Dunno if it helps ya or not, but thats what i found! :D

Jill
04-11-2010, 09:50 PM
Phil,
I have the Seloc manual that covers 1965 to 1990. V6 and L6. It has all sorts of diagrams and pictures for whatever application you have. I'm finding like Jeff mentioned its just like some of the newer OMC controllers where the wiring for tilt/trim, temp and tach come out the front of the controller thru a female plug, like mine. But of course the proper tach should be used for whatever your setup is. I still have trouble wrapping my brain around some of the electronics or electrical systems especially on the troublesome topic of tach's.

Good luck

You'll nail it eventually I'm sure of it.

Oh and how cool that there are guys, or gals, out there rewinding stators for these old motors.

Rod-B
04-12-2010, 07:07 AM
Phil, heres what i found out for ya...

On the face of my Airguide tach(looks just like yours) at the very top of the face there is a marking P-6487...i can faintly make out your numbers but they look the same so that tach will work for your motor if its functional. On the back there is a 3GA stenciled on in yellow paint. 2 black wires which appear to be factory, are spliced into the wires coming out of the tach.

Those two black wires run to the plug on the front of the control box. There is a third brownish\tan wire which i cant trace where it goes but im assuming back to the motor. The male part of the plug looks like this: = | One of the black wires goes to the top horizontal male connector and the other black wire goes to the vertical.

As far as i can tell, this is all factory original to this boat. Dunno if it helps ya or not, but thats what i found! :D

The P-6487 isn't the model number....just the ID number for face design I'm pretty sure. Model numbers on the Airguide compass face style were on the back in a sticker. Not real sure what the inked on numbers and letter signify. Some of the earlier Airguides did have model numbers on the face...653 and 654...but they required a sending unit for either magneto or battery/coil to work. A link to a chart someone else put together below. Might be of use to someone sometime. Again, no wiring diagrams there.

http://www.classicboatwork.com/classicparts/gauges/airguide/airguideinstructions/Airguide%20Tachometer%20Application%20Guide.pdf

Jill
04-12-2010, 09:12 AM
Hey Rod....isn't this your tach and converter thingy I borrowed? (1st 2 pics)

And check out this beasty tach that came with my 1960 V-75 Johnson. (2nd and 3rd pic)

Jill
04-12-2010, 10:46 AM
Some example pics of what I have but there are so many options as to where the wires go.

Typical on plug last pic

9 O'clock Black ground
11 " Tan alarm buzzer or temp gauge if you have temp sender
1 " Grey Tach sender many options as to where it gets the signal from.
3 " Purple S on Trim gauge
6 " Brn/wht I on Trim gauge

Rod-B
04-12-2010, 12:42 PM
Hey Rod....isn't this your tach and converter thingy I borrowed? (1st 2 pics)

And check out this beasty tach that came with my 1960 V-75 Johnson. (2nd and 3rd pic)

Could be. I know I loaned you one at one time. That one is a 653 for magneto ignition so could be used with either the older OMC twins with mag ignition or the early V4 OMC with mag ignition. Don't remember which you were thinking of trying it on...seems like the twin for prop testing?