75 j20 wiring issues

[ClassicQueen]

Hi, this is my third attempt at posting
I recently acquired at 75 J20 AMC 360. Truck runs I have not drove it due to concerns with wiring. Ignition button cranks truck without key. Fuel pump runs only when key is in the ON position or all the way towards driver. Gauges do no appear to work except for oil pressure gauge. Neither wiper or lights work. There are parking lights missing, which i could probably source. The battery cannot be kept connected as it gets drained. Voltage regulator is disconnected and appears to have been decommissioned for a long time.
The way things look, I might need to replace all wiring, there are plenty of cut off wires in the cabin as well.

https://photos.app.goo.gl/ZGGifavePd4xjpWPA

[joe]

Ouch! Rather than trying to patch/save whatcha got... I'd punt. Get a paper copy of the original 75 TSM and wiring diagram and just dump the butchered orig harness. EZWire and Painless offer a generic truck harness. Both are good quality, easy to install, labeled and include a new fuse box. The orig 75 FSJ harness wasn't great in the first place so trying to save it after DSPO butchering IMHO is futile.

[letank]

as Joe said, it is a bit of a challenge to redo a wiring system, because one need to understand how the original designers laid out the wires, which is always a puzzle.


the coil pictures has a ceramic resistor to bypass the resistor wire that is part of the original wire loom that runs on the passenger side of the valve cover. Usually those wires get cooked because they are too close to the exhaust manifold.


Starts with the cranking/ignition/charging system to keep it simple



Being a 75 you may still have the prestolite ignition distributor, which has 2 white plastic vacuum canisters on the distributor, those have a bad reputation and where used for years 75-77 or about. One user claim that they can be refurbished or kept up for little care, most people move to the post 78 system called the duraspark


as for charging, time to do the ammeter bypass


EDIT: do not forget to remove that coil to battery wire when you turn off the engine, otherwise the coil will still be powered with a potential risk of fire


EDIT2: for any aftermarket wiring such as painless, you still need to reuse your original wire plugs at the firewall

[fsj454]

cabin harness

I have a good harness for 1975 glass fuses and steering column

[ClassicQueen]

ok, is it better to get a harness kit or an original harness?

as Joe said, it is a bit of a challenge to redo a wiring system, because one need to understand how the original designers laid out the wires, which is always a puzzle.


the coil pictures has a ceramic resistor to bypass the resistor wire that is part of the original wire loom that runs on the passenger side of the valve cover. Usually those wires get cooked because they are too close to the exhaust manifold.


Starts with the cranking/ignition/charging system to keep it simple



Being a 75 you may still have the prestolite ignition distributor, which has 2 white plastic vacuum canisters on the distributor, those have a bad reputation and where used for years 75-77 or about. One user claim that they can be refurbished or kept up for little care, most people move to the post 78 system called the duraspark


as for charging, time to do the ammeter bypass

[ClassicQueen]

I'm definitely interested on column mine is pretty beat.

I have a good harness for 1975 glass fuses and steering column

[fsj454]

transmission

What type of transmission do you have

[ClassicQueen]

Not sure of type but it is automatic

What type of transmission do you have

[tgreese]

ok, is it better to get a harness kit or an original harness?

Better depends on you. Any hot rod harness will require that you route and terminate the circuits and understand (to some degree) what you are doing. It will be different from the factory wiring, so you will need to rely on your notes and the instructions from the kit to diagnose and repair any issues with the new wiring.

The factory harness can be put back exactly like it came from the factory, and the factory wiring diagram can be used for any subsequent diagnosis and repair.

Personally I would fix the factory wiring unless there had been a fire. You can straighten out the mess if you go one circuit at a time and repair the PO's sloppy changes.

Or, get the harness from fsj454 and install that. Supposedly Zach at Z&M Jeeps (?) has replacement harnesses for these vehicles. Might be worth looking into. http://www.ifsja.org/forums/vb/showthread.php?t=187862

Here's some help with harness repair: https://www.jeepforum.com/forum/f8/b...arted-1340134/

[ClassicQueen]

Where could I get a wiring diagram for the the year? I looked in the web and wasn

[tgreese]

Suggest you buy the TSM. Less than $25 on CD-ROM from RockAuto. No '75 diagram online that I know of.

https://www.rockauto.com/en/moreinfo.php?pk=417941&cc=1309474&jsn=371

[rang-a-stang]

If you go here you can get the 76 TSM in searchable .pdf. It should be close enough. They also have the 74-76 Parts manual which you should download, too. They are super handy.

http://oljeep.com/edge_parts_man.html

Someone makes a new/reproduction harness for these. ZM Jeeps maybe?

In my experience, I find it easiest to fix a factory harness, even one that is butchered as bad as yours. I usually take one circuit at a time and trace it out. Takes a long time but you learn EVERYTHING about how your truck is wired and what is connected to what.

I usually print up a couple copies of the wiring diagram (from the TSM) and just start marking them up as I go. As you verify the harness/circuits, highlight it as done on the diagram. Remove all the extra crap that has been added to your truck that is aftermarket. If there is an aftermarket radio, chuck it. If there is a brake controller, remove it. Etc. Then verify the circuits that need to work even when the key is off (headlights, horn, brake lights, interior lights, etc.). When those all work correctly, move on to the engine. Starter, coil, alt, gauges. When those work, work on anything left over (radio, clock, heater, A/C, etc.). I recognize I just listed about 12 hours of work (or more) but I think it is the best way to fix wiring. I have completely re-wired a vintage car and I have rebuilt harnesses and this seems the most reliable way to be done messing with electrical gremlins.

I also recognize you are going to find ALOT of problems because it sounds like the previous owner(s) worked around bad parts rather than fix them (hence a starter button that cranks without a key). You will find connectors that are totally corroded. When you do, clean or replace them.

Supplies to buy in bulk: Electrical tape (for bundling wires, MUCH better than zip ties), Shrink wrap (to cover terminals as you install/fix them), male and female terminals. Wire labels (I often times use a small label maker if i have to replace a wire with another wire of a different color, I label both sides of it).

[ClassicQueen]

Thanks for the info! Very helpful. I will be printing the 76 wiring diagram. It

[ClassicQueen]

So is ignition always on bc voltage regulator was bypassed?

If you go here you can get the 76 TSM in searchable .pdf. It should be close enough. They also have the 74-76 Parts manual which you should download, too. They are super handy.

http://oljeep.com/edge_parts_man.html

Someone makes a new/reproduction harness for these. ZM Jeeps maybe?

In my experience, I find it easiest to fix a factory harness, even one that is butchered as bad as yours. I usually take one circuit at a time and trace it out. Takes a long time but you learn EVERYTHING about how your truck is wired and what is connected to what.

I usually print up a couple copies of the wiring diagram (from the TSM) and just start marking them up as I go. As you verify the harness/circuits, highlight it as done on the diagram. Remove all the extra crap that has been added to your truck that is aftermarket. If there is an aftermarket radio, chuck it. If there is a brake controller, remove it. Etc. Then verify the circuits that need to work even when the key is off (headlights, horn, brake lights, interior lights, etc.). When those all work correctly, move on to the engine. Starter, coil, alt, gauges. When those work, work on anything left over (radio, clock, heater, A/C, etc.). I recognize I just listed about 12 hours of work (or more) but I think it is the best way to fix wiring. I have completely re-wired a vintage car and I have rebuilt harnesses and this seems the most reliable way to be done messing with electrical gremlins.

I also recognize you are going to find ALOT of problems because it sounds like the previous owner(s) worked around bad parts rather than fix them (hence a starter button that cranks without a key). You will find connectors that are totally corroded. When you do, clean or replace them.

Supplies to buy in bulk: Electrical tape (for bundling wires, MUCH better than zip ties), Shrink wrap (to cover terminals as you install/fix them), male and female terminals. Wire labels (I often times use a small label maker if i have to replace a wire with another wire of a different color, I label both sides of it).

[tgreese]

So is ignition always on bc voltage regulator was bypassed?

What do you mean? Ignition is off when the switch is off.

Where was the VR bypassed? List the wire numbers from the diagram.

Realize that the 6-cylinder Jeeps got the Delco alternator with the regulator inside the alternator. The V8s got the Motorola alternator with an external regulator. Both of these schemes are shown on the same diagram, V8 above and 6 below. It's up to you to understand this and separate the two cases.