engine and drivetrain Tach Not Working How To Diagnose

[paulram]

I've read a bunch of previous posts on tachs not working.  Mine does not work either.  I need to diagnose and get the tach working in order to do timing and not blow up motor.

 

A little history (I really have no history) but....

 

The engine was replaced at some point and the wiring is a mess.  It's fubar but runs.  

 

It looks all the wires were cut and spliced back together.  Unlike most threads I've read, I have wires running from my coil but no working tach. Can anyone tell me what color wire would be coming from the tach into the engine compartment on a 76 '02? There are wires not connected to anything.  I need to confirm there is wiring to the tach as well.

 

Here is a picture of my coil (running pertronix), a random green and white wire, and a picture of my spliced wiring mess with random wires not hooked to anything.  I don't know where to begin.

 

 

Sorry if I am asking the wrong questions but tracing/testing i am an amateur...Gin and tonics...expert and can give advice.

[Napes]

It's a little hard to say - you have a real mess there.  But, having said what you probably already know, in the third picture down the wire laying on top of the valve cover may be your missing tach connection.  Try plugging that into the spade connection at the condensor on the side of your dizzy (distributor) and see if that results in a functioning tach.

 

Good luck with the rest.  You need to get yourself a wiring diagram and multi-meter and begin the process of tracing down your wiring.

 

Bob Napier

'75 2002A

'76 2002A (wife)

[paulram]

Does anyone have a visual of the wiring and how it connects into the engine compartment on a 1976.  I'n not looking for wire colors and connections but specifically how it is mounted and looks.  Looking for the correct harness/adapter and how it is connected to the body itself. My version of being wedged into what seems to be a washer fluid mount surely is not what the German engineers envisioned.

 

I need to start undoing the wrongs and it is a long list.

 

Besides no tach, no dash lights, no fans etc.  Driving in the rain is a big problem with no defrost

[FunkyLaneO]

The wire is solid black and is not bundled with the blue sheathed wires, it should have a double wire connection on it.  originally the wire went from your tach to the negative terminal on your coil, there it had a double wire going to a single spade connector, from there the other wire in pair went to your distributor, if you have pertronics that wire is unplugged and probably set aside somewhere as it is no longer needed, try to find that black wire and plug it into your negative coil terminal.

 

if that wire is already plugged into your coil then check the back of the gauge and make sure teh single black wire is plugged in there as well.  the tach is a pretty simple piece of equipment to troubleshoot, it has power, ground, and signal (the black wire) check each of those and if they are all present when the key is on then the gauge may be faulty.

[FunkyLaneO]

Also, if you are not in California, Desmog that car and you will eliminate alot of the wiring that is causing you grief.

[paulram]

These are two of the wires that are coming through from the cabin.  A base exposed black wire and a brown wire.  I will try to figure out where these go to.

 

Wish there was an easy way.

[FunkyLaneO]

it may be easiest if you remove the cluster, the single black wire plugged into the back of the cluster on the tach side is your signal wire, you can use a multimeter to test where it goes.  Also, if you haven't already, check all of your fuses, the solution may be easier than you think.

[M3M3]

 

 

Good luck with the rest.  You need to get yourself a wiring diagram and multi-meter and begin the process of tracing down your wiring.

 

Bob Napier

'75 2002A

'76 2002A (wife)

 

 

 

if that wire is already plugged into your coil then check the back of the gauge and make sure teh single black wire is plugged in there as well.  the tach is a pretty simple piece of equipment to troubleshoot, it has power, ground, and signal (the black wire) check each of those and if they are all present when the key is on then the gauge may be faulty.

 

 

it may be easiest if you remove the cluster, the single black wire plugged into the back of the cluster on the tach side is your signal wire, you can use a multimeter to test where it goes.  Also, if you haven't already, check all of your fuses, the solution may be easier than you think.

+1 on these three.  gotta get a wiring diagram and a VOM.  start wringing out the wiring harness wire by wire with continuity checker

to confirm where it comes from and where it goes. 

[paulram]

I guess I need to be more familiar with using a continuity tester/multimeter to diagnose random wires. 

[paulram]

Still could use a photo of stock wiring config in the engine compartment.

[FunkyLaneO]

Still could use a photo of stock wiring config in the engine compartment.

My car has been desmogged so it looks nothing like yours, I will try to get a picture tonight anyway.

 

To identify the wire, turn your multimeter to ohms and connect one lead to ground and one to the black wire that plugs into your tach, then prop the meter so that you can see it through the windshield and find the black wire in the engine compartment, touch this wire to ground and see it the needle on your multimeter moves, if it does it is the same wire, if it doesn't, keep looking.

[FunkyLaneO]

Where does that yellow wire go that is plugged into the negative side of our coil? does it splice into another wire? it does not appear to be original (it could be part of the 76's smog wiring), maybe a PO had an aftermarket tach installed at some point?

 

Follow it to wherever it goes and report back, maybe take a picture of what it plugs into if you don't know what it is.

[paulram]

As for the 4 wires from the coil,

 

I have a red and black running to the Pertronix, a black and brown running into a blue sleeve just above the coil and then the yellow.

 

The yellow wire is spliced into an black wire in the receptacle that has been previously cut and reaattached.  Honestly I have no idea when it comes to wiring and where this harness was originally and what the orange piece plugged into it does.  I have work to do.  I'll report after I figure out the function of the existing wires.

 

That mystery wire on the valve cover may hold the key to something...

 

Fubar.

[FunkyLaneO]

Sounds like the yellow wire splices into your old tach wire, check the splice to make sure it is good.  Any wire that goes into the blue sheathed bundle is part of your smog system (except the resistor wire that is clear in color that goes to the positive terminal of the coil)

 

The wire that is sitting on your valve cover probably plugs into that sensor that is on the intake manifold (between cyl 3 and 4) that is part of the smog system.

[paulram]

There area bunch of wires in the blue sheath.  These are all for smog (except resistor wire)???  I'll wait before I start ripping out wires until I find out more.

 

Also, what is this piece.  It is hooked to the carb via vaccum hose.  Smog as well??  I didn't trace the wire.

 

Thanks.