3rd gen's tail light voltage

Hi folks,

I installed a 12v power outlet today on my '90. I had wanted to have it switched, so thought I'd use the no-longer-used license plate light wires (a PO cut off the fender including the plate light). I checked the voltage at the plug and found it was 11.5 volts even though the battery was 12.7. Then I unplugged the tail light plug and found that it was also 11.5 volts. Does anyone else lose 1.2 volts between the battery and the rear lights?

Must be a secret Honda thing to make the bulbs last longer!

Cheers,
Glenn

 

Only way for the voltage to be lower is to have a "voltage drop" across some other resistance in the circuit, it just doesn't disappear! The classic formula E=IR always applies. it's physics. Check all your grounds and connectors for some slight corrosion (resistance). Start at the battery and work back towards light.

Where did you put meter leads when you measured voltage? Try putting black (-) lead on the ground terminal of the battery, then measure voltage at light. If still 11.5, then problem is in wiring to the light. Reverse the procedure, put the Red (+) on the battery and the black on the ground of the light.

 

Yes, I was wondering if there was a component in the tail light circuit such as the tail/brake lamp sensor on the Sabre. I saw there wasn't after I looked at the schematic.

I just checked at the wire connectors for the license plate light and the 3 wire plug for the tail light with (-) to chassis ground. Then checked battery voltage across battery (+) & (-). I'll dig deeper and see what I find.

Thanks,
Glenn

 

Voltage drop through connectors and wiring is to be expected with age, one reason it is a good idea to run your coils straight from the battery through a relay. Power through connectors in the harness, ignition switch and kill switch all drop the voltage

 

Yes, Norm, absolutely right. Funny you should mention that! I just finished wiring the coils on my Triumph Trophy 900 to the battery through a relay and new 14 gauge wire 3 days ago. It starts quicker and runs smoother at low revs now that the I have eliminated the 20 or so connectors between the battery and coils.

Cheers,
Glenn

 

OK, I took the seat off for another look tonight. Yup, still losing a volt between the battery and the tail lights. So, pulled the tail light fuse and lo and behold, only 11.5 volts at the fusebox. I pulled all the fuses, sprayed contact cleaner on all the fuse contacts, scraped them all a bit with a little 1/8" screwdriver and checked the voltage again. 12.6 volts at the fusebox now!

Still only 11.5 at the tail lights, though, so I have to clean up the rest of the connector contacts - later. Got some riding to do first and everything still works. And the tail light bulbs will last longer!

Cheers,
Glenn

 

I use a small emory board (for fingernails) to get into connectors and burnish pins.

 

Great idea. I found (in the schematic) 10 plugs and 2 ground points between the battery and tail light that have a physical connection to that circuit. I'll get to them when she is fully stripped next time (unless something happens to the electrics before then).

Cheers,
Glenn

 

Since the lights are low amperage, there won't be any significant heat generated. It is the Stator connector that carries 30 amps that normally melts, make sure you clean that one if you haven't already direct wired it.

 

Yes, thanks. I checked it a few months ago and it was still like new. I have done the 3 yellow wire fix on my previous Honda's. I will check it again.

Cheers,
Glenn