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I think I opened a big old can of worms

I have been having a lot of problems with a whining noise in my radio and CB. I've put a filter on the power lines and hooked it directly to the battery with no luck. So being the "I want to fix it all" type of guy, I started looking under the hood for a bad ground. Well I have replaced the engine, carb, distributor, and gotten rid of all the emissions stuff and there were a lot of connectors tie rapped to the fire wall where I left them after disconnecting them. Well I started to pull the unused wires out. After

3 hours and a couple of dozen wires the Jeep started. The only problem is the Tac will not work, so here are my questions:

Where does the tac get its signal from?

What are the 2 relays, 2 capped connectors, and 4 wire circuit board that are between the fender and the battery?

Next I want to go under the dash and remove the computer and all the crap under there, what is the easiest way to get it out??

Well I'm back to it tomorrow, thanks in advance for all advice.

Scott

90YJ 4.2L AX15
Reply to
Foot Loose
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The tach on a YJ 258 gets it's signal from the computer.

I was told you can just move the tach pickup wire to the coil to finish dumping the computer in the garbage.

On a CJ7 258, the tach is inline with the ignition module power.

One of those relays powers up the manifold heater and tags the electric choke via the oil pressure switch. The other one 'might' be an idle relay to turn on the sol-vac for an auto or air. It would need the computer working to fire.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Foot Loose wrote:

Reply to
Mike Romain

Easiest way to eliminate non-RF electrical noise (at least that I have found) is to use a .1uf mylar cap to ground from the B+ line. It helps to add one at the closest practical point to the radio, and others at the offending devices (motors/alternators) be sure to restrain the cap properly, and insulate the leads.

Not perfect, but simple, and eliminates most noise sources.

tach picks up signal from switched side of coil.

Reply to
A.H. MacIntosh aka USERNAME

Electrolytic

An electrolytic cap may not have a low enough ESR (equivalent series resistance) at the frequency of interest... they are also polarized, so if you hook one up backwards, you will either have not much capacitance (best case) or it will explode like a firecracker (what usually happens). Best thing to do is to put *both* a big e-lytic and a small (.1uF) cap across the alternator output (big red wire) and ground. There are special caps called 'feedthrough' that can be spliced into the big wire and grounded.

You really should first determine whether the noise is coming in the antenna lead, or the power supply wire. This is easily done by disconnecting the antenna and seeing if any improvement is noticed. If this helps, you need to address the noise at the source, usually the alternator or distributor/coil.

If the noise is coming in the power lead, you can install a noise suppressor, available at Rat Shak. This consists of an inductor (like a transformer, a coil of wire around a piece of iron) that will allow DC to pass but blocks AC. You put it in series with the power lead going to the radio, follow the directions. __ Steve .

Reply to
Steve Cowell

I use a Mylar cap, I seem to remember 600V, but that was only because it was a junk box item. anything over 100V is great. One at the radio, and another (if needed) at the alt output. (the one at alt is to catch any RF before it uses the lead as an aerial.

the cap passes AC/pulse dc (aka whine) to ground.

Reply to
A.H. MacIntosh aka USERNAME

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