Electric tach fluctuating

Hey guys, I have an 83 seca 750 completely stock with original 21,832 miles. A while ago (4 months ago) I notices at high rpms 6-8k the tach would flicker back and forth, but only going over a bump in the road. Now 4 months later the tach flickers starting at about 3,500 rpm and continues to do so as the rpms go up. I took the back of my dash off to check is any of the connections were loose, none were loose. I don't know where to go from here. I do know however, that the electric tach is controlled and connected to the ignition coils and TCI box. Any and all help is apprectiated. This isn't a big issue, it's just quite annoying to look at and I dont want it to become any worse. Thanks for all the help, hope to hear from someone soon.

 

the tach takes its "pulses" from the grey wire that feeds one of the coils, make sure this wire doesnot touch any of the ignition ht leads, as it could be picking up stray pulses, also a bad connection ,maybe in the headlight shell ,could cause the same symptom.
trace the grey wire through, from the coil to the cluster , you should find your fault.
stu

 

How are the revs? Any stumbling as you really lean on it under load?

 

Thanks for the quick reply. I forgot to mention I did go into the headlight bucket and traced the wire from the gauge to the connector in the bucket. I cleaned the connector and it still did the same thing. I did not check if the wire is touching any of the hot leads from the coils. Quick question.. Which one is the hot lead, and could I find it in the wiring diagram?

 

oh , and the brown wire feed to the tach and the black earth wire, also need checking, the multipin plugs in the shell, can push the pins out of the back of the plug, if the "barbs" are not located correctly
stu

 

Un

Under load, 4th gear roll on starting at 25-30mph 2k rpm, the tach is smooth and doesn't hesitate. However it sticks under hard acceleration at 3k rpm

 

ht leads are the big thick ones that go to the sparkplugs.
stu

 

Oh gotcha. I can check it when I get home, at about 11:30 am.

 

I checked everything and the grey wire was not touching any of the ht leads from the coils. Could this mean a coil(s) and or TCI is going bad? I put my timing light on it and there was no hesitation in the light and the ignition correctly advanced itself. So I'm at a loss now for the issue I'm facing.

 

A bad ground for the tacho circuit can cause this to happen, there's a common ground somewhere in there, you'll have to trace it on the wiring diagram to see which connector it is fitted into and where it goes from there.

 

Thanks Len, I'll definetly have to look at that today. Would the ground have a specific color and or be located close to the tach or coils? Thanks for the help

 

That can also be caused by a cold solder joint or a trace on the board that is lifting. If you don't find a break in the wiring harness the next place to look is the tach internals.

 

Would that require me to take the tach, include gauge, out of the dash, or is it possible to look it without removal of the whole assembly?

 

Ground wires are always black on these bikes. There are typically a couple of harness common ground wires that attach to the rear coil mounting bolts, but those are common for the entire wiring harness (there may be other points of common grounds, too, it varies by bike). The ground for the tach is part of the same 3-place connector that has the brown (hot) and grey (signal from the coil) wires in it; note that this black wire "disappears" into the main harness somewhere and is tied into the main harness common ground wire (which then exits the main harness to the aforementioned common harness ground wire somewhere).

Since the rest of the electrical isn't acting strange (due to bad grounds), it is doubtful that the termination of the common ground is the problem; It is also doubtful that the tach ground splice into the main harness is the problem; the most likely places would be the e-place connector shell (on either side) or at the tach body itself.

 

Unfortuantely not. Even the screws that the wiring for the tach connects to lie behind a cover, and the tach internals can't be accessed without dismantling the gauge cluster. IT' not hard to do, but it does require time and patience. Check the locations that Chacal mnetioned before you go any further than removing the rear cover of the gauge cluster.