Can't get my stock tach to work - JeepForum.com
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post #1 of 19 Old 08-08-2012, 06:10 PM Thread Starter
thompsong
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Can't get my stock tach to work

I bought an 85 cj 6 cyl. Totally redid it and put a/c in it. When I began to actually run it my tach didn't work. I had to pull the tilt steering wheel back out and I decided to get the tach working. I did a nutter bypass on the jeep early on. I know there are two red wires, one with a white tracer off the ignition switch and the other goes somewhere in the harnass, I think back to the positive side of the coil, that connect to the tach wires; I had them connected. When I put a volt meter on the wires the one with the white tracer shows me battery voltage as it should. The other does nothing. I ran a wire from the positive side of the coil to the plain red wire on the tach and I connected the red wire with a white trace from the tach to the red wire with the white trace from the ignition switch. I saw a faint spark between the wire ends and tach pointer jumped and went back to 0. I've studied all the wiring diagrams and read on several forums trying everything. Aside from the tach in the jeep I have two other OEM tachs laying on the floor that I try everything with as well, they all have done the same thing every time. When I connect the red trace wire from the ignition switch to the other red wire through a voltmeter, (neither wire comes from the tach) I get battery voltage. The only other thing I might try before going to an aftermarket tach is to connect to the Black wire from the ignition module and be certain it has a good ground. Other than that, I've about exhausted everything I know to try. Any suggestions?

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post #2 of 19 Old 08-08-2012, 06:41 PM
John Strenk
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Just to be sure, the jeep does run, right?

When you disconnect the tach at the ignition switch, does the engine die?



Disconnect it at the plug shown above.

If it still runs. Then the power is being bypassed and that is why the tach does not work.


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post #3 of 19 Old 08-08-2012, 06:45 PM
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Easy, it is not wired in to the middle of the right wire and as it is a "passthrough" type connecting it up like a normal tach will not work.

On a stock CJ of that year there should be a connector on the ignition feed under the dash, a short distance from the column connector. It is white plastic from memory and has a red with white tracer wire going in and out. You unplug it, plug in the two plugs on your tach and hey presto. The CJ tach is supposed to sit in the middle of the ignition feed and is a "pass through" type i.e. the wire goes in one side and comes out the other.

Of course we live in the real world and your chances of having the connector just sitting there unmolested is slim. If you have not got one (and they were all fitted with them) then you need to find the red with tracer wire that feeds the ignition.

There are two that come off the column connector. One goes to the fuse box and feeds various things including the emisisons computer.

The other goes to the tach, then on to the bulkhead connector and feeds the ignition, connecting to the coil +ve.

It is this second wire you need to isolate and put your tach in the middle of that line.


The red wire (with no tracer) is nothing to do with the ignition. Depending on size it may be the main feed to the fuse box.


PS John beat me to it, that black looking tach plug is the one you need to find and connect into the middle of

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1984 CJ7 258ci - Puthijeep
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post #4 of 19 Old 08-10-2012, 07:12 PM Thread Starter
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John,

I have the steering column out and to start the jeep I jump from the battery to the solenoid and then jump across from the battery cable connected to the solenoid to the post that engages the solenoid to send current to the starter. It runs and I have battery current to the red wire with the white trace coming from the ignition switch. I then run a wire from the plus side of the coil to the solid red wire going to the tach and it shows movement but only at the instant of touch of the wire. I have done the nutter bypass. I really painted the fenders before putting the ignition module on and am suspect it is not grounding well. I ran a separate ground wire tonight but was not able to check to see if it made a difference. Is there any way I can test this thing with the column out. I have an ac unit on it and it is in the road of getting to the tach. I suspect I could take the ignition switch off the coumn and connect it to the connectors. Thanks for your help.
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post #5 of 19 Old 08-11-2012, 05:19 AM
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Quote:
Originally Posted by thompsong
John,

I have the steering column out and to start the jeep I jump from the battery to the solenoid and then jump across from the battery cable connected to the solenoid to the post that engages the solenoid to send current to the starter.

It runs and I have battery current to the red wire with the white trace coming from the ignition switch.

I then run a wire from the plus side of the coil to the solid red wire going to the tach and it shows movement but only at the instant of touch of the wire.

I have done the nutter bypass. I really painted the fenders before putting the ignition module on and am suspect it is not grounding well. I ran a separate ground wire tonight but was not able to check to see if it made a difference. Is there any way I can test this thing with the column out. I have an ac unit on it and it is in the road of getting to the tach. I suspect I could take the ignition switch off the coumn and connect it to the connectors. Thanks for your help.
When you have the steering column out, does this mean you have the ignition switch out also?

I'm thinking just connecting the ignition switch up and sliding it to the "run" and "start" positions and seeing if it works. All this jumpering around is probably why it doesn't work. It will probably be fine when everything is connected.

You can take the switch off the column and just use a small crew driver to slide the switch into various positions


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post #6 of 19 Old 08-11-2012, 06:51 AM Thread Starter
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Yes, the switch is on the column and the column is out. I will take the switch off the column and plug it back into both connectors and then move it to run, reconnect the tach and see if it works. Everything was hooked up correctly and the tach didn't work. I had to pull the column for another reason unrelated to electrical and while it was out I decided to get the tach working. Thank you for your help. I'll repost this evening.
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post #7 of 19 Old 08-11-2012, 10:24 AM Thread Starter
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I put the switch on the plugs, set to run, hooked up the tach in the jeep and started it. The tach didn't work. I pulled the wires apart on the tach with the jeep running and it shut the jeep off. I hooked up another 6 cylinder tach I had and the exact thing happened. Neither tach worked but when I unplugged the wires the jeep shut off. I hooked up an 8 cylinder tach and it worked. When I unplugged the wires, the jeep shut off. I guess I have two bad 6 cylinder tachs. I have another jeep with a 304 and a 6 cyl tach in the jeep that works. Looks like a tach swap.
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post #8 of 19 Old 08-11-2012, 02:39 PM
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Well at least you found an answer.
If you are not going t o do anything with the tach, I'd like to pull one apart and examine it.
Sort of a "Post" mortem.


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post #9 of 19 Old 08-11-2012, 08:05 PM Thread Starter
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John, you're welcome to the one that was in the jeep. How do I get your address? I'll send it to you.
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post #10 of 19 Old 08-12-2012, 10:36 AM
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A lot of good information John Strenk
I have a problem with my stock tach as well, I'm showing on my stock tack 1000 rpm at idle, my hand held tack/dwell meter says around 700 at idle. The more I rev the engine the distance between the two gets farther apart, the jeep came with a 6 cylinder shortly after buying it i installed a 360, Would the motor swap be the problem?? or is my gauge just screwed up...

**** it, GAS IT!
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post #11 of 19 Old 08-12-2012, 12:12 PM
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Quote:
Originally Posted by thompsong
John, you're welcome to the one that was in the jeep. How do I get your address? I'll send it to you.
Look for a PM


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post #12 of 19 Old 08-12-2012, 12:27 PM
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Quote:
Originally Posted by ericksin
A lot of good information John Strenk
I have a problem with my stock tach as well, I'm showing on my stock tack 1000 rpm at idle, my hand held tack/dwell meter says around 700 at idle. The more I rev the engine the distance between the two gets farther apart, the jeep came with a 6 cylinder shortly after buying it i installed a 360, Would the motor swap be the problem?? or is my gauge just screwed up...
Yep, the tach still thinks its a 6 cyl and you are getting 2 more pulses per revolution.

Some people changed some resistors inside to get it to work but I never tried it yet.

Think how impressive the RPMs will look to your friends in the mean time.


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post #13 of 19 Old 08-12-2012, 03:56 PM
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Thank you very much

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post #14 of 19 Old 08-14-2012, 07:23 PM Thread Starter
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John,

Tach enroute or should be there. Please let me know what you find.
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post #15 of 19 Old 08-14-2012, 07:27 PM Thread Starter
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By the way John, have any diagrams showing how the turnsignal wire connectors are wired. The ones that you have to take apart to pull the steering column. I have an extra black wire coming down from the turn signal switch that is not hooking up to anything yet I think everything but the tach worked before I pulled the column.
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