1975 Johnson 115HP V4 tach wiring

[timwc1953]

Hello, I have a 1975 16' Grady White boat (run about) with a 115 V4 Johnson. I have not run this boat for a couple of years and the tach has stopped working. It is a Airguide Sea Speed tach. It only has 2 wires coming from the back side. I have traced these using my shop manual for this. One wire goes to the #7 terminal on the rectifier. Where should the other go? Just want to be sure it is connected properly.

 

[ezeke]

Re: 1975 Johnson 115HP V4 tach wiring

Hello, I have a 1975 16' Grady White boat (run about) with a 115 V4 Johnson. I have not run this boat for a couple of years and the tach has stopped working. It is a Airguide Sea Speed tach. It only has 2 wires coming from the back side. I have traced these using my shop manual for this. One wire goes to the #7 terminal on the rectifier. Where should the other go? Just want to be sure it is connected properly.

The second wire goes to ground. If the tachometer does not work when wired this way, test your rectifier.

 

[timwc1953]

Re: 1975 Johnson 115HP V4 tach wiring

OK that's what I thought. Thanks for the info, but the engine cranks and runs fine. Would that be possible with a bad rectifier?

 

[ezmobee]

Re: 1975 Johnson 115HP V4 tach wiring

Yes I believe so. Your battery isn't charging though.

 

[ezeke]

Re: 1975 Johnson 115HP V4 tach wiring

Yes I believe so. Your battery isn't charging though.

Correct. Heres the link: http://forums.iboats.com/showthread.php?t=190638

BTW, Always disconnect the battery before testing the rectifier or other ignition related components.

 

[Wishiniwuzfishin]

Re: 1975 Johnson 115HP V4 tach wiring

Hey tim: Can you post any results you have with your tach? I have a very similar situation as you. I just bought a 1974 Glastron with a 1974 Johnson 115HP. It has an Airguide Sea Speed tach also which the wires going to it have been cut. There is a yellow and a black wire coming out of the back of the tach. Is that the same as yours? I was going to connect the yellow wire to the gray tach lead in my control box and the black to a ground but would like to be sure that is right first. I also removed my tach from the dash to check it out and there is a small terminal strip on the back with 4 terminals. Mine has a jumper between the number 1 and 2 terminals. There was a little sticker with instructions for the jumper but I couldn't read most of it. I have to believe the jumper between 1 and 2 is correct because it looked and felt like the tach had never been removed before I did it and it would have beeen very hard to change the jumpers without removing the tach from the dash. I live in NE Ohio so it has been hard to get days nice enough to run the motor in my drive with muffs so I haven't been able to hook up the tach and try it yet. Hopefully soon. Would appreciate any thing you find out about yours.

 

[timwc1953]

Re: 1975 Johnson 115HP V4 tach wiring

Hey Wishin, I tried to reply earlier but this laptop would not co-operate. I think we hae the same exact tach. Mine has only 2 wires coming from the back side, one yellow and one black. The yellow wire goes to the control box and ties in to the grey wire there. There is a tag on the back of the tach that says for a 4 cylinder you would need to hook up a jumper between 1 and 4. Mine neverr had this jumper however and was working about 3 years ago when I stopped running the boat. I am currently restoring this boat and trying to get everything working. I am thinking there may be a broken wire somewhere, so I will run a temporary wire from the motor #7 terminal to the tach and make sure that the ground (black) is good. Sorry the weather is so bad up your way. I am in NC and it's not much better here. I will let you know hwat I find out on the tach.

 

[Wishiniwuzfishin]

Re: 1975 Johnson 115HP V4 tach wiring

So yours doesn't have any jumper wire at all on the terminal strip? And it worked previously like that? Can you read the number at the very top on the face of the tach? Mine is P6487. I think it is a model number. The jumper wire on my terminal strip is a small (maybe 20-22 ga.) red wire about an inch long jumping 1 and 2. What does your instructions say for jumping 1 and 2. Like I said mine looks original but I can't say for sure. Another side question...what kind of gear oil do you use in your gearcase and has it been trouble free? Thanks alot and feel free to ask if I may be of any assistance to you.

 

[ezeke]

Re: 1975 Johnson 115HP V4 tach wiring

To Wishiniwuzfishin: Your gear oil needs to be high viscosity marine gear oil. The specification was for OMC/BRP Hi Vis, but most marine outboard gear oils rated 75/90 or within that range are acceptable.

 

[timwc1953]

Re: 1975 Johnson 115HP V4 tach wiring

Hey Wishin, the label on the back of the tach reads as follows:
1- 2cyl Magneto, no connection
2- Alternator System connect 1 and 2 terminals
3- 3 cyl CD connect 1 and 3 terminals
4- 4 cyl CD connect 1 and 4 terminals
As I said before, mine never had a jumper on any of these, I am going to test my rectifier as instructed by Ezeke. Also I use Evinrude/Johnson Ultra-HPF Gearcase Lube in the lower unit. I have not experienced problems with the lower unit, but did have to repair my remote control box, as the shift lever broke inside. Also replace both cables while in to that. Oh yes, my tach has the P 6487 in the very top of the face side. However on the back side the number 690 BB is on there. I believe that is the model number. Hope this info helps.

 

[timwc1953]

Re: 1975 Johnson 115HP V4 tach wiring

Thanks for the proceedure ezeke. I tested the rectifier as instructed. Did not get ANY readings either way so I guess it's safe to say I need a rectifier. I have found some at a couple of places, some made by Sierra and some made by CDI. Is one better than the other?

 

[Wishiniwuzfishin]

Re: 1975 Johnson 115HP V4 tach wiring

Hey Tim: Did you do anything more with your tach or rectifier yet? I finally got to run my motor in the driveway with the muffs today. I had wired the tach up before I put the battery back in....yellow wire direct to #7 terminal, black wire to ground. Got motor running and nothing on tach. Still messing around with the motor right now so I'm gonna check the rectifier later after I disconnect the battery. The motor seems to run pretty decent so at least I'm happy about that.

 

[Wishiniwuzfishin]

Re: 1975 Johnson 115HP V4 tach wiring

I checked the rectifier with the ohmmeter...needle didn't move on any tests. But then I went back and looked at the test instructions posted above and didn't see anything about disconnecting battery first. For some reason I thought I read to disconnect battery first so thats what I did. Now I'm wondering if I should have left battery connected and if the results would have been different. Won't be doing anything else with motor till at least tomorrow so hopefully I'll get straightened out by then.

!!! P.S. Just went back and read the post again. It did say to disconnect the battery in the original post but not in the instruction link...And I looked in my factory service manual and couldn't find anything about disconnecting battery. Any help anyone?

 

[ezeke]

Re: 1975 Johnson 115HP V4 tach wiring

You have to disconnect the rectifier to test it and the components that are being tested are the diodes within the rectifier.

The reason to disconnect the battery is to safeguard the ignition system while you play around with the wiring. It's good shop practice to disconnect the battery when performing any wiring tasks.

 

[Wishiniwuzfishin]

Re: 1975 Johnson 115HP V4 tach wiring

Thanks for that info. I removed the rectifier from the motor so I could have it in hand when I ordered another. I guess since it did no damage to the motor running it with a bad rectifier that it is ok to run the motor with no rectifier connected at all ? I'm still going over the motor and would like to run it while waiting for a new rectifier. I know the battery won't be charging but thats no problem.

 

[timwc1953]

Re: 1975 Johnson 115HP V4 tach wiring

Hey Wishin,
I have ordered a new rectifier too. Another reason to disconnect the battery while testing diodes (in the rectifier) is that if power is left on, you can fry the diodes when reconnecting the rectifier. Glad to hear you got the motor running. My motor runs fine while in the driveway hooked up to the water hose, but I really want to get the tach working again. I also have to repalce the speedometer pick up tube (pitot) as the old one broke off where the tubing connects. Speedometer works though when putting a little pressure through the tubing. Looking forward to warmer weather and getting the boat in the water again.

 

[Wishiniwuzfishin]

Re: 1975 Johnson 115HP V4 tach wiring

I ordered the CDI rectifier off of this site. Hope the tach works when I get the new rectifier on but I'm more worried about charging my battery than having a tach. I'm just using this boat for fishing. If I ever decide to do a restore I'll be more concerned with it. Man, that is weird about your speedo. A few days after I bought this boat I was messing around with it in my drive. I was kneeling or laying under the transom checking something, can't even remember exactly what I was doing now, but I heard a CRAAACK. Got up and looked around and couldn't see anything. Was starting to get peed off cuz I knew I heard something so I looked on the ground and found a piece of white plastic. Couldn't figure out what it was at first, then it hit me. I looked at the transom and sure enough...I broke the speedo pickup tube off!! Sounds like every thing that happens to your boat happens to mine. I hope you get your rectifier in first and your tach works cuz then I'm sure mine will too.

 

[Wishiniwuzfishin]

Re: 1975 Johnson 115HP V4 tach wiring

My tach works !!!! Ordered the CDI rectifier off of iBoats Fri. 3/5....Got it in the mail Mon 3/8...(super service by iBoats). Put it in today and wired up the tach and it works. I'm glad I checked the tach or I would have found out the hard way my battery wasn't charging. Now...on to my next project.

 

[timwc1953]

Re: 1975 Johnson 115HP V4 tach wiring

Hey Wishin, Glad to see you got your tach working. I just got my rectifier yesterday and had time to install tonight. My tach works too! Fired the engine briefly and watched it go. Thanks Ezeke for the info! Now just gotta clean up the boat on the outside and it's ready for the water.