Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 14, 2025 ...

Strange taillight wiring

October 06, 2021, 11:28:30 am

I have just got to post this!!
When I first started thinking about hard wiring my Isuzu taillights I was extremely, and I do mean EXTREMELY cautious about what bayonet connector went to what bulb/function. I used my battery charger, hooked a clamp to the ground bayonet in the connector.
As I got each light to light up I wrote down what each bayonet did what.
Well, yesterday the DW and I went out to the coach and I took out the driver's side taillight assembly I had hardwired. It had worked but the DW was always telling me that the Isuzu lights were dimmer than the passenger side.
So, I compared the male connector with the coach female connector.
I found that the coach connector had all five female connections all on the right side, while the taillight assembly had the male bayonet connectors in different positions!! The brake light male connector was over where there was no female connector in the coach connection!! But the brake lights worked! Explain that!
So I brought the taillight assembly in the house and relocated the male connectors to match the coach connections (which I checked with a probe light and the DW). I then went out and plugged the lights into the coach.
Now everything light up on the back end, bright brake lights, except for one little thing. NOW the amber turn signals light up--on both sides!!
MY LED lights up above the regular lights work just fine.
So, looks like I will be doing more investigating.
But I still am baffled as to why the taillight connectors were not compatible with the coach supply connection. Different age Izuzu taillights than what was originally installed by FOT??

Quote Selected

Re: Strange taillight wiring

Reply #1 – October 06, 2021, 07:50:16 pm

I have no idea what you did or is going on but I do know the Isuzu lights run on a circuit board. Don't know if that matters or not. That's what usually goes out. Can you rewire around the circuit board? I have no idea.

Quote Selected

Re: Strange taillight wiring

Reply #2 – October 06, 2021, 10:12:38 pm

I already rewired the circuit board using actual wire, new sockets, solder, Shoe Goo, aluminum pop rivets.
I have also reworked two sets of lights for other members on this Forum.
So I am not dealing with the old green plastic circuit board with the copper printed "tracks" on them that corroded and then malfunctioned.

Quote Selected

Re: Strange taillight wiring

Reply #3 – October 07, 2021, 09:14:25 am

Hey Norm,
When do the turn signal lights light up? with headlamps on? when the turn signals are on?
What was originally causing the dim lights on the driver's side was due to the lack of a power feed  causing the electricity to find an alternate source. Electricity is like water. It will find the easiest flow. Without diodes, etc. to help keep it dammed up, it will go where ever. Do you remember on the green printed circuit there was a white colored rectangular object? That little jewel helped keep all the electricity running in the right direction. Now, I need to know about the turn signals as to when they are on.

Quote Selected

Re: Strange taillight wiring

Reply #4 – October 07, 2021, 09:33:38 am

OK, here is what I discovered so far.
Turn signals function when The DW turns the turn signal stalk in the left or right position. Haven't tried this when brake lights are on.
Turns out the reason lights were dim was because there wasn't any female bayonet feeding electricity to the taillight male connector.
Moved the male connection over to match the coach wiring and now taillights (brake & run) are bright. But amber turn lights are now on. I didn't touch those connections.
After I get my toilet flange base gasket and the toilet installed I intend to go thru both sides of the coach wiring and resolve this issue.
Again, what is weird is that the bayonet connectors on the coach and the Isuzu taillights assembly didn't match up.
I know for a fact that I quadruple checked how the Isuzu taillights were wired, so that I could put them back in and they would work.
Never thought the connector pattern would be different than the coach!!

Quote Selected

Re: Strange taillight wiring

Reply #5 – October 07, 2021, 10:16:20 am

Norm,
You aren't losing it. The wiring on the plug ins at the tail lamp assy's are NOT quite the same. You would think so, but, again, due to the internal "wiring" on the factory printed circuits, and the internal diode setup, they are slightly different side to side. As I said, due to backfeed on the ground side due to no supply on the connector you were talking about, that is what caused the bulbs to dim. Electricity is like water. It will find its way one way or another. It takes the path of least resistance. If the "dam" (diode) is out of the pathway, and say you have a burnt out bulb elsewhere, there are issues. Which leads to your current problem. Be sure ALL the bulbs related to the turn signals, IE front signal bulbs, dash signal indicators, etc. are all good. If you have time, please let me know about when the turn signals are both on. It will help me help you, if you see what I mean. Good luck on the "thunderdrum"!!!!!!

Quote Selected

Re: Strange taillight wiring

Reply #6 – October 07, 2021, 01:29:57 pm

Current Problem...

Quote Selected

Re: Strange taillight wiring

Reply #7 – October 07, 2021, 01:51:33 pm

One of my greatest frustrations was wiring a toad. I finally gave up and spent 325 bucks on a wireless bar from Tow Mate. Plug the sender into coach, plug the bar into toad- switch on-drive away

Quote Selected

Re: Strange taillight wiring

Reply #8 – October 07, 2021, 03:04:07 pm

Only wish my problem was that easy!
I check every connection and bulb when wiring up a vehicle for towing, be it an auto or a trailer.
That is why I am so dumbfounded with the way the taillight connector on the coach didn't match the connector on the Isuzu lights.
Raining right now so trouble shooting taillights and wiring will have to wait until tomorrow.

Quote Selected

Re: Strange taillight wiring

Reply #9 – October 09, 2021, 09:04:40 pm

Well, here is the latest on my lighting issue.
Went out this morning and tried every possible combination of lights. All running lights good. All turn signals good. All backup lights good. Even the brake lights are good-------BUT---the amber turn lenses light up when I put on the brakes.
The turn lights work just fine and flash when I have the brakes on, but just stay on when brakes are applied.
All my LED lights work as they are supposed to.

So, rather than beat a dead horse, I closed up everything and left the lighting alone. I did take the crappy looking inside covers for the taillights and sanded them smooth and painted them a nice shiny white. I just couldn't stand all the spray foam beads on the outside of the covers. I also went up one size in the screws that hold them on. Two of the old screws had actually fallen out and were in the storage boxes under the lights. I slotted the two outside holes (one on each cover) so that rather than having to do the touchy-feelie thing to locate a screw hole and possibly/probably drop the screw, I now leave the screw closest to the outside wall one turn loose. Now I will only have to remove the inner screws closest to the radiator and then slide the covers inward to remove.
End of story.
Next project is installing a new convertor/battery charger when it arrives.

Quote Selected