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post #1 of 11 Old 05-04-2017, 06:27 PM Thread Starter
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Tach with Deleted Spark Computer

Hi,

Quick question... I'm going through the process of deleting the old spark computer in my carb'd GLH and am wondering how get a signal to the tach without the spark computer, which supplies it. Can I run a wire from the negative post on the coil to the bulkhead/tachometer? Could it/would it/might it be so simple?

p.s. I want to keep stock tach
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post #2 of 11 Old 05-05-2017, 06:09 AM
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Re: Tach with Deleted Spark Computer

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Originally Posted by Dominic View Post
Hi,

Quick question... I'm going through the process of deleting the old spark computer in my carb'd GLH and am wondering how get a signal to the tach without the spark computer, which supplies it. Can I run a wire from the negative post on the coil to the bulkhead/tachometer? Could it/would it/might it be so simple?

p.s. I want to keep stock tach
What year is this?
According to my wiring the tach is supplied a signal from the - coil on the carbed cars so doing away with the Spark Control Computer should have absolutely no affect on tach operation.
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post #3 of 11 Old 05-05-2017, 06:26 AM
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Re: Tach with Deleted Spark Computer

Just looked at your profile and saw the car is an 86 which is not directly from the - coil to cluster.

- Coil runs to the SCC Connector 1/Cavity 1 and the Tach Signal comes from Connector 2/Cavity 4.
The controllers on the injected cars use a different type of signal to operate the factory tach and that tach will not operate correctly connected directly to the - coil nor will an aftermarket tach operate correctly connected to the controllers tach signal.

Does that hold true on the carbed cars?

Either run a jumper wire from the - coil to BH connector cavity #31 and see what happens or wait for someone that has done this to reply.

Jan
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post #4 of 11 Old 05-05-2017, 11:02 AM Thread Starter
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Re: Tach with Deleted Spark Computer

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Originally Posted by NAJ View Post
What year is this?
According to my wiring the tach is supplied a signal from the - coil on the carbed cars so doing away with the Spark Control Computer should have absolutely no affect on tach operation.

Thanks Jan,

looking up the part numbers and found the TACH is the same in both the 84 and 86 rallye clusters (part # 4051 833)...

so THEORETICALLY, if the 84 has a coil-to-tach reference signal, then the same signal should work in my 86....


Jan, back to you again... could you scan the TACH wiring diagram and any associated pages from the 84 FSM? I have the 86 FSM and would like to compare....


Cheers,
Dominic
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post #5 of 11 Old 05-05-2017, 12:34 PM
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Re: Tach with Deleted Spark Computer

Quote:
Originally Posted by Dominic View Post
Thanks Jan,

looking up the part numbers and found the TACH is the same in both the 84 and 86 rallye clusters (part # 4051 833)...

so THEORETICALLY, if the 84 has a coil-to-tach reference signal, then the same signal should work in my 86....


Jan, back to you again... could you scan the TACH wiring diagram and any associated pages from the 84 FSM? I have the 86 FSM and would like to compare....


Cheers,
Dominic
84 & 86 should be the same. 84 is when Chrysler made the big wiring change to the L-body. New dash, new cluster, new interior harness, etc.. My 83 uses the coil - for tach pickup, so it's easy to wire. But I don't know about the 84+. Since the carbed spark computer is a pretty simple controller compared to the turbo stuff, I would doubt they do much for signal conditioning, but you never know.

I would have to look in my 83 FSM to see if they show the tach pickup going to the ECU or to the coil. My 83 had a standard gauge package when I bought it, and I converted it to a Rallye cluster, so I just hard wired the tach to the coil.

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post #6 of 11 Old 05-05-2017, 01:50 PM
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Re: Tach with Deleted Spark Computer

The wiring i have is not from the FSM.
I will send you what i have through PM.
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post #7 of 11 Old 05-05-2017, 02:02 PM Thread Starter
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Re: Tach with Deleted Spark Computer

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Originally Posted by NAJ View Post
The wiring i have is not from the FSM.
I will send you what i have through PM.
Thanks Jan!

Got 'em!

you remind me that I need to reinstall Mitchell OnDemand on my laptop....
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post #8 of 11 Old 05-05-2017, 02:18 PM Thread Starter
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Re: Tach with Deleted Spark Computer

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Originally Posted by 83scamp View Post
84 & 86 should be the same. 84 is when Chrysler made the big wiring change to the L-body. New dash, new cluster, new interior harness, etc.. My 83 uses the coil - for tach pickup, so it's easy to wire. But I don't know about the 84+. Since the carbed spark computer is a pretty simple controller compared to the turbo stuff, I would doubt they do much for signal conditioning, but you never know.

I would have to look in my 83 FSM to see if they show the tach pickup going to the ECU or to the coil. My 83 had a standard gauge package when I bought it, and I converted it to a Rallye cluster, so I just hard wired the tach to the coil.
Question: What year Rallye did you install, the newer 84-up (tach & fuel gauge combo) or the older 83-style (tach & warning lamp)?

Thanks,
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post #9 of 11 Old 05-05-2017, 02:22 PM
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Re: Tach with Deleted Spark Computer

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Originally Posted by Dominic View Post
Thanks Jan!

Got 'em!

you remind me that I need to reinstall Mitchell On Demand on my laptop....
I do not have access anymore, lost that in 2010, good thing I printed, scanned and saved all of the many years of TD wiring to my computer and two flashdrives over the years.
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post #10 of 11 Old 05-05-2017, 04:11 PM
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Re: Tach with Deleted Spark Computer

Quote:
Originally Posted by Dominic View Post
Question: What year Rallye did you install, the newer 84-up (tach & fuel gauge combo) or the older 83-style (tach & warning lamp)?

Thanks,
I installed an 83 cluster. My goal to make it look correct. 84+ won't go in earlier cars without the harness. They changed all the connectors.
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post #11 of 11 Old 05-05-2017, 10:14 PM Thread Starter
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Re: Tach with Deleted Spark Computer

Aww... That answer fills my heart with sadness...


Thank you.
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