Under Dash wire interference - JeepForum.com
 
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post #1 of 5 Old 03-18-2019, 09:24 AM Thread Starter
Nick4320
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Under Dash wire interference

Ive been trying to clean up and fix some of the gauges on my dash and as of recently i have noticed that when turning on my wipers with the jeep running, my Tach spikes. Ik the tach is from crown so clearly not the best, and im sure the PO put in a wiper switch from crown or Omix-ada. Im assuming since the wires on the tach are just laying on top of the rest of the rats nest, its picking up some interference. Occasionally when turning on the head lights the tach spikes as well.

Would simple plastic wire loom threaded onto the tach wires help out or do you think there's a different problem (i.e. RATS NEST.... i cant stand the rat nest of wires under there)

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post #2 of 5 Old 03-18-2019, 10:28 AM
81CJ5360T19
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A possible fix would be to install a capacitor to absorb the interference the wiper motor is emitting. You can try using an old points type capacitor wired to the ground wire of the wiper motor. Make sure the capacitor is properly grounded.

Last edited by 81CJ5360T19; 03-18-2019 at 10:29 AM. Reason: Words
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post #3 of 5 Old 03-18-2019, 10:42 AM
John Strenk
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Like 81CJ5360T19 is saying. It could be the brush noise generated in the motor that could be giving you some problems. It would be hard to run the tach off a different accessory circuit because they are ultimately tied together. A nice capacitor or even looping the feed wires around some ferrite rings would help. You would have to figure out if the noise is coming in on the power side of the tach where filtering is important or if it is pickup on the signal wire where shielding or distance should be important.

Usually if the circuit is in good shape meaning there is little voltage drop throughout the circuit, a little brush noise is no problem. But if there are poor connections causing a drop in supply voltage then the brush noise could have a greater impact on the tach.

I would also recommend running good grounds.
Poor grounds can effect the voltage going to a sensitive device causing a change in performance as much as poor connection supplying power to the device. This refers to the headlight issue.

Put them both together just multiplies the problem.


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post #4 of 5 Old 03-18-2019, 12:04 PM Thread Starter
Nick4320
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Yeah I had a feeling loom wasnt going to do anything for me really. I can see a weak ground being a possible cause for the tach, its screwed just into the bottom of the dash. I pulled the ECM at the beginning of winter, so I still go the through firewall rubber plug, i might look at bringing in a dedicated ground, and possible a constant Hot as well through there.

A quick search found me some of these https://www.amazon.com/uxcell-UF90B-.../dp/B016FC066O

pretty sure these are to big but this would be idea, clip it on so im not cutting up a bunch of wires, I dont have the dash off so kinda doing things half blind.

And as for voltage drop, i just rehooked up my voltage gauge (plug fell out) and im noticed a drop (14-15v dropping to 10-12v) when anything thing turns on. Ik this isnt true by checking the battery and alt with a meter
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post #5 of 5 Old 03-18-2019, 01:28 PM
John Strenk
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Yes, need to test voltage at the point where the device draws it's power. Testing the battery won't really help unless the battery is bad.


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