Curious Lighting Issue on 79 FJ40

[Mike Shull]

Success!

View attachment 3833338

That resistive short between turn and tail lights is now gone. I assume it was caused by the cobbled trailer wiring or the trailer wiring adapter box.

When are you available To come look at mine?

Nice job!

 

[CruiserInProgress]

Well done. That's the value of persistence and assuming nothing. Plus it never hurts to walk away for a while so you can come back with a clear mind to check what is actually there. And you didn't even let out the magic smoke

Ha! Thanks for the support.

You're right about the value of walking away and returning fresh. This project has been confusing and frustrating at times, because just about everything I touch needs to be reworked in some way.

But, with every challenge there's a success of sorts after working through it, getting me further down the road, so to speak. Looking forward to getting plates on it.

 

[knuckle47]

There has to be a great business making and selling new complete wiring harnesses…problem being so many year to year changes.

 

[CruiserInProgress]

Thanks Mike,

When are you available To come look at mine?

Nice job!

Thanks Mike,

It's a bit of a drive for me, but happy to give you some tips to walk through diagnosing the lighting issue on your 40. I learned a few things during the process on my previously abused project, like the one Charlie mentioned, to not assume anything.

 

[CruiserInProgress]

There has to be a great business making and selling new complete wiring harnesses…problem being so many year to year changes.

I have read that @Coolerman used to do complete FJ40 harnesses. But, you're probably right, so many years, variations, obsolete connectors, etc. that doing a turnkey harness business would be challenging.

He's been a great resource for me getting started on my FJ40, connectors, specialty wiring subassemblies, and his downloads of schematics and other docs.

 

[Coolerman]

I STILL build rear chassis harnesses and all the small sub-harnesses for most FJ25/40/45 trucks. I just stopped building main cowl harnesses due to time, lack of some special connectors on the 1974-83 trucks, and unfortunately money. The amount of time it takes to build and test a full harness set is measured in 10's of hours. If I charged standard shop rates of $75.00 an hour, a 1974 or later FJ40 harness set would be over $2400.00. Most folks just can't afford that...

The reality of most FJ40 main cowl harnesses is that unless they have been in a fire, or literally cut into pieces, they are pretty easy to repair. Simply untaping a harness will reveal the wires under the tape to be in great condition. It's usually only the engine compartment wires that are exposed to heat that need replacing.

On the issue above. That WestBar three wire to two wire conveter uses simple diodes to do the conversion. Not only would that cause the "bleed" issue you have, it would also have resulted in pretty dim trailer lights. The diodes drop .7 volts just doing their job. The trailer lights would have had at best 11 volts on them and probably more like 9 or 10 volts due to voltage drops at connectors and old wire having a higher resistance. If you want to tow with your FJ40, use a converter like the Curt 59196 POWERED converter. It does require a power feed from the battery, but isolates the wiring on the trailer from the FJ40 wiring. So a short in the trailer wiring will not take out the FJ40 wiring. This converter powers the trialer lights directly from the battery so the trailer lights are much brighter compared to the diode based converters.

 

[CruiserInProgress]

I STILL build rear chassis harnesses and all the small sub-harnesses for most FJ25/40/45 trucks. I just stopped building main cowl harnesses due to time, lack of some special connectors on the 1974-83 trucks, and unfortunately money. The amount of time it takes to build and test a full harness set is measured in 10's of hours. If I charged standard shop rates of $75.00 an hour, a 1974 or later FJ40 harness set would be over $2400.00. Most folks just can't afford that...

The reality of most FJ40 main cowl harnesses is that unless they have been in a fire, or literally cut into pieces, they are pretty easy to repair. Simply untaping a harness will reveal the wires under the tape to be in great condition. It's usually only the engine compartment wires that are exposed to heat that need replacing.

On the issue above. That WestBar three wire to two wire conveter uses simple diodes to do the conversion. Not only would that cause the "bleed" issue you have, it would also have resulted in pretty dim trailer lights. The diodes drop .7 volts just doing their job. The trailer lights would have had at best 11 volts on them and probably more like 9 or 10 volts due to voltage drops at connectors and old wire having a higher resistance. If you want to tow with your FJ40, use a converter like the Curt 59196 POWERED converter. It does require a power feed from the battery, but isolates the wiring on the trailer from the FJ40 wiring. So a short in the trailer wiring will not take out the FJ40 wiring. This converter powers the trialer lights directly from the battery so the trailer lights are much brighter compared to the diode based converters.

Thanks for clarifying the harness work you still do. Nice to have you as a resource.

About trailer hitch wiring, I think I may have read a post of yours discussing the merits of the Curt style converter, and running directly off the battery for better trailer lighting and reduced risk of frying your rear harness wiring.

I certainly learned a lesson on what not to do from the PO! My rear lights are looking good and working well once I removed all traces of the old trailer converter.