Trailer zapped my Combination Meter!

Hi Tacoma owners.....

I'd like to confirm with others who may have had something similar happen before I spend the $$ to replace my Combination Meter.

I drive a 2019 Tacoma Off Road version and the truck has been rock solid with the exception of a few weird electrical issues (i.e. Dome light switch, and now this one). I tow a pop-up camper in the summers so I know the tow wiring system has worked fine in this truck since I bought it new in 2019. However, this weekend I borrowed a car trailer from a buddy and hooked up the 7-pin to my factory-installed tow receptacle and no lights. I decided to drive it home so I could work on it and troubleshoot the issue. I left i plugged in, which is probably where I made my mistake.

Long story short....I popped the 30A Towing fuse so I knew something was not hooked up correctly on the trailer side. Sure enough...when I took apart the 7-in connector on the trailer, the battery + was shorted and pretty much toast. I replaced the trailer connector with a new 7-pin but problems persisted. I also checked all the fuses associated with towing system on the Tacoma (main fuse box in the engine bay, small fuse box driver side kick panel) and did not find any additional popped fuses. I used my Multimeter to ring out all the fuses and everything is okay. I even checked all the relays associated with the towing system and they are all working correctly. I traced the power on all the circuits for the towing system and all fuses and relays seem to be working but turn signals and brake lights do not work....only the left one stays on all the time (even when the truck is off). The running lights are working fine.

I've spent hours reviewing threads on this forum (thanks for the schematics) and have narrowed down the issue to the Combination Meter. Here is what I currently know:

• When truck power is OFF, I am still seeing power (12 v) on the Left Turn pin (STTL on the trailer socket).
• When truck power is ON, power (12v) is correct on BATT, GND, and TAIL, and I've confirmed the trailer brake is sending power to the BRK pin.
• When truck power is ON, the Left brake light is on all the time, regardless of the turn signal. The Right brake and turn signal do not work. I never see any power (12v) on the right light and the left light is constant all the time (regardless of blinker or brake).
• All the lights are working properly on the truck...the issue is isolated to the trailer towing circuit.
• When I check for voltage at connector IA3, pin 19 there is no voltage (blinkers, hazards on) but when I check for voltage at connector EB3, pin 5 there is voltage (12v). And there is the voltage at STTL on the 7-pin receptacle....all the time (power on or off). I can't figure out why don't see voltage on IA3 - pin 19 since the schematic shows these in series.

Here are my questions:

• After much reading on the forum, it appears the issue is within the Combination Meter, which is $550 and you have to replace the entire unit. Can anyone else confirm my logic or if I'm missing something? Why would I be seeing 12v at EB3 but not at IA3? I'm 95% sure the issue is within the Combination meter and when I hooked up the crappy Zappy borrowed trailer, it must have zapped it (my fault for trying to save $$), and somewhat disappointed a fuse did not protect that circuit. Any suggestion on where to buy one online vs. my local dealer who only sells at MSRP?

Thanks in advance for your help!

 

@caribe makaira is the guru

 

If trailer connector is hosed, then juice will back feed to other circuit. Verify when is it that you do have juice at eb3 and not IA3. Also, fried might be in a few places, interrupting flow.
Unfortunately the towing circuit is integrated into the Combo PCB. Also, some states require dealer to tag the replacement combo for future milage issues.

 

Thanks for the quick response @caribe makaira!

I have power at EB3 all the time (Truck power on/power off) and none at IA3 (pin 19) in all test scenarios. From my testing, I never have 12v from the Combination Meter for Left or Right blinker or stop light (I'm assuming power comes from the Combo meter for the brake as well since it's just the blinker light on solid).

My assumption is the same as you, something has fried and its back feedback feeding 12v from somewhere else.

I live in Colorado and will call the dealer tomorrow to price the Combo meter and protocol.

 

You could remove the Combo Meter, then remove the back cover and take a visual.

 

Towing turn & stop is the combined towing feature on each wire (Left & Right). Towing Tails has it's own fuse and relay activated in parallel with vehicle Tail relay.

 

Also take a look at the T12 towing connector at the rear bumper. It also can be removed and opened to verify crispness...