Tachometer wiring/ 8BA

banjoQ

banjoQ

Senior Member
I have a Stewart Warner tachometer, model#D760G. It is a 6 volt unit with a three wire harness, green-black-white. I have done some reading in the archives to better understand the wiring.I know the green is the impulse wire and goes to the dist. and black goes to batt., white should be the light. Using jump wires to test the connections and the tach, am finding the engine stalls when making the battery connection. i am making a mistake here but don't see the problem. Does anyone have any ideas where these connections should be made? As always, your help is greatly appreciated.
 
Unfortunately, I see that $10 on eBay will get the Installation Instructions for your tach. Dang capitalism.

Have you tried leaving the dist wire off and just connecting to battery and ground? I would expect nothing to happen. Then flick the dist wire once or twice to battery and does the tach needle move slightly? Personally, I don't like connecting wires to the dist points and expect no noise from the radio as those wires are antennas and the distributor points are creating multifrequency hash.
 
Paul- thanks for the reply, I will give your idea a try just to see if the is any reaction. The tach had the mounting instruction with it, but no wiring diagram. I have put a few of these in other newer cars so I thought I would be OK. Have done a search for wiring diagrams on the net but unable to find one. My search results in a link to a different, possibly newer model..
51merc- thanks for the reply. I had already found that out in my search throuh the archives. The puzzler is why is it shortin out and killing the motor? Clearly, I am missing something here.
 
Some of those SW tachs required a conversion box to make them work. I had to use one on mine, my tach came from an early 60's Studebaker, so I was able to get the box from Studebaker International.
Do some research on line to see if your tach needs one, or give them a call and ask them.
 
I just went back to the eBay photo and was able to learn there is a 'sender' unit soas not to wire the tach directly to the distributor. Makes sense, but where is the 'sender'? You obviously do not have it. Please let us know what you end up doing to make the tach functional.
 
I saw a thread on the H.A.M.B. about this. I think there is an outfit that makes a clone of the control boxes for these old tachs. Do a search and you'll probably find it. I think the "clone" boxes sold for about $50.
 
including a pic of the tach, notice the additional "can" mounted to the tach. My thoughts on this were that this was the sending unit. The cable coming out of the back has a three pin plug. I gently opened the plug by opening small tabs and slid back body of plug to identify color coding of pins. Black, white and green. Supposedly this tach is NOS. Had mounting brackets and mounting instructions, light harness in original box dated 1952.
I need to find a way to test the unit without risking any damage. Been on SWs' website and have yet to find any info on servicing their products. Plenty of new stuff to buy and info on where to get it. I think I will take it over the hill to a old school speed shop tomorrow and see if they have any ideas. They have been in the business since the 50s' and might remember handling these. Will keep you posted. Again, thanks for your thoughts on my problem.
 

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Just an update on this issue. Called Stewart Warner in Texas today. Got to talk with a "technician". No sooner explained what I had and he started saying he was sorry, can't help. He claims they have no info on older equipment, certainly not from the fifties. Lots of excuses and insisted he could be of no help.
I have a call into Del City, they say they will look into it and call me back. Its been awhile, not getting my hopes up. Will keep plugging away on the net. Might be I have a piece of shelf art. Its a shame, this thing is pristine.
 
If it is built like the early stewart warners with external drivers you have a battery hidden under the lid somewhere...
Open up the back and have a look...
 
So I opened up both units today to have a look. The tachometer is clean and dry with no corrosion. No visible shorts or burnt wires. The can behind it appears to be the drive motor for the gauge. I have determined that this was intended for a V8 and that it most definitely used a sender unit. There also would have been a extension cable with three pin plugs. This probably allowed for mounting the sender on the firewall. As Paul mentioned, there are re-printed instructions and wiring diagrams available on ebay. At this point I am going to spend a little more time investigating the sender units availability. The harness can be made up from wire and connectors. I guess it was too good to be true. Thanks to all who shared their ideas.
 

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Top fuel and Tubman, thanks for the info. Made contact with both companies. Let you know if it works out.
 
If it´s like the normal Sun and SW units with a sender the meter itself is just mA meter and not for a V8 or L6, it´s the sending box that sets which motor it will work with.
Is there components inside or only the coils ?
The early senders is just a relay and a couple of capacitors.
How the senders work is real simple, when the coil sends a pulse to the sender the relay closes letting a capacitor charge from the battery inside the box.
When the relay opens again it send the stored energy from the capacitor into the meter.
So pulsed current drives the meter.
 
There is a company called TechnoVersions that makes a sender unit called " tach match". They claim that this unit will serve most vintage gauges that required a sender unit. They offer a few different versions. It is adjustable for different engines ( 2-4-6-8 ) , and provides for calibration. My concern after reading the specs are that it seems to require 12 volts to power it. Currently I am using a generator on a 6 volt system. I emailed them to ask about any options I might have, will see what they have to say
 
banjoQ said:
Just an update on this issue. Called Stewart Warner in Texas today. Got to talk with a "technician". No sooner explained what I had and he started saying he was sorry, can't help. He claims they have no info on older equipment, certainly not from the fifties. Lots of excuses and insisted he could be of no help....
Click to expand...

That is sad. When I started reading this post, that is what I was going to suggest. They have been very helpful to me in the past with sending unit info on 60s/70s temp and oil gauges. It's too bad that they wouldn't even try.
 
"banjoQ", If you have a 6 volt system, it is probably also positive ground. This is a double whammy against being able to use that tachometer. My partner and I have just finished development of a device to run a 12 volt negative ground tach on a 6 volt positive ground system. Believe me, it wasn't simple. We have some units out in field test now. You might be able to use one of our units to drive one of the clone senders to drive that tachometer, but that's a pretty high price to pay just to be able to use the tachometer. It might be worth it, though; that's up to you.
 
Tubman- you are correct, 6 volt pos. ground system. And it is a double whammy deal breaker. I heard back from the folks at Tach Match and they pretty much said the same thing. Their "clone" box needs 12 volts and neg. ground. My 6 volt system works great and i really dont want to convert to 12 volt at this time. Looks like I have a piece of art for the desk for now. I have one more option and that is to find an original SW sender,6V. You never know, one might turn up. Lots of respect for Tach Match for getting back to me in such a short time. Thanks to all who weighed in on this.
 
The old senders had batteries in them and they where left there...they leaked corroded and often ruined the relay.
Even when you find a NOS unit they came with battery installed from what i understand so it´s not sure they are good even if new in the box.
 
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