Electrical short/grounding issue?

[Banebadboo]

Hello all,

 

I'm doing a restoration/mod to a 1988 Jeep Comanche, I'm using the wiring harness from a 1993 Jeep XJ.  I was in the process of finishing the engine bay assembly and wanted to do some testing of my wiring. I have been testing as I went but this was the first time applying power with everything in the engine bay and cab hooked up.  I found that I had a short at the positive battery cable.  I have been able to trace the issue to the headlight switch after pulling the fuse (#11 Headlamp Delay Module, Horns, Security Alarm) the short stopped however, if I pulled the headlight switch on the short returns.  I have not finished connecting the front headlight wiring harness it's installed but not connected, the rear light harness is not installed yet I just have wires pulled to the back.  Could not having all the grounds in that part of the harness cause my issue or do you think it's more likely to be a bad(new) light switch or wiring issue that the switch?  I hate opening the dash, it went in perfect.  

 

Any thoughts or ideas?

 

Thanks

[Bloo]

Not having grounds won't cause a short. A short is when current gets to ground too early, without having to first flow through the device it was supposed to flow through.

 

It is tough to guess since I have not worked on either of those vehicles since the 1990s and I don't have the books.

 

For starters I would look for a pinched wire in that headlight circuit.

 

Good luck, and I hope you get it sorted.

Edited January 30, 2022 by Bloo (see edit history)

[Banebadboo]

I didn't think the grounds would cause my issue, I have seen a lot of weird issues due to grounding so thought I would ask.

 

 

[NailheadBob]

I would unplug the connector at headlight switch and perform an ohm test of each wire from headlamp switch connector to its location it feeds, BUT you will need a wire diagram to do this, IF you do not have the diagram possibly you can get that  from your library, our Library has all of this on computer and need a library card to use it for free, if you make copies of diagram it is 10 cents per copy, if any questions let me know.

 

 

Bob

[joe_padavano]

Are those two harnesses even compatible? The late 80s and early 90s saw numerous changed in onboard electronics.

[Banebadboo]

Thanks for the suggestion.

 

A little info on the restoration/mod.  As I said the truck is an 88 but I'm using the engine, transmission and transfer case from a 93 Jeep Cherokee XJ plus the entire wiring harness(modified for a Comanche).  The truck has lots of other mods such as upgraded the doors to a 97 Cherokee XJ, using the power seats from a 2001 Grand Cherokee.  We are going to using this truck to pull our travel trailer when we retire.  Here's a link to the build if anyone's interested.  

 

[roysboystoys]

Seems like you need to investigate the security system. You might need to cycle the key?

[jdome]

It is not clear to me as to how you measured this "short at + post" and with what instrument you measured it with? If you are using a light probe or a digital meter that beeps at you doing a continuity check with 1 lead clipped to ground and other lead clipped to battery lead (battery NOT connected) and you get a continuity indication, that doesn't necessarily mean you have a zero ohm dead short. It could mean you have a closed circuit or path (continuity) from the battery lead through a fuse - light switch - bulb (gauge/accessory)) then to ground. That is a good thing. Even though you don't have your head & tail bulbs in, or sockets grounded, you may have your dash lights, gauges, devices connected & properly grounded to the dash you installed. All your devices are grounded on one side and connected thru fuses & switches to the primary power post at the fuse box so you could be reading multiple paths. 

 

If you test with an ohm meter, 1 lead to ground & 1 to primary lead (no battery) with fuses out & switch off and no "continuity", then you have a clean line -  battery to switch/fuse. Switch on, fuse in, bulb in with continuity indication: then your path to ground is on the bulb side of switch.  The "continuity test beep" usually only works on a high scale such as R X !0,000. switch the meter down to R X 10 or R X 1 scale and you should be able to read a 1 or 2 ohms or less which would be a typical bulb filament or gauge. A good thing. Ignore the "beep" or turn it off on low scale.  1 or 2 ohms is too low to read on a high scale and will appear as a "short" on high scale.  To be sure, take the battery side probe and touch it to a good ground spot and you should get 0 ohms on the low scale as apposed to some small measured resistance thru the bulb.

[Larry Schramm]

Does the truck have any "after-market" anything like alarm systems, radio, remote start, etc...?  If so, take it out and throw it away.  I have run into too many vehicles with gremlins that go directly back to the after-market stuff.  Just my experience having seen a bunch of issues.