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Toyota Repair/electricial Problem


QUESTION: Hi Ted I have a  1990 Toyota corolla DX Sedan. This is my VIN JT2AE94A7L3399529. I hope this is all you need to answer my question? I only have one live power to taillight relay on a 1990 Toyota corolla sedan with key off, supposed to have 2. I know I shorted something out. do not know which port in the taillight relay socket is ground. have 4 ports on socket with only one powered up. the other one that needs power I think goes to the taillights 15 amp fuse which has no power. Diagram shows power to 2 sides of relay from white wire. when you turn on all lights power from taillight relay should close to send power to the 15 amp. taillight fuse which gives power to taillights. does not because only one power source to relay.

What I have tried so far?: turned key off turned on light switch checked power to taillight relay socket with only one powered up. used ohm meter to find ground.What should the meter be on in the ohm section of the meter to check ground and what readings should I get to tell which one is ground? Any input you could give would be very helpful.

ANSWER: To check ground in an electrical system all power must be off so disconnect the battery, check from each relay contact to body ground, if your meter is not auto ranging set the meter to it's 0-100 ohm range, a good ground will read 0-1 ohm. On a digital meter the display should read 0.00 - 1.00 ohms, Keep in mind that the headlight switch switches ground to work either tail lights or both head and tail lights so the switch has to be in the headlight position to complete the circuit.

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QUESTION: my problem is the relay should have 2 sources of power with key in the off position and I only have one. the one that is is not powered up I think is supposed to send power to a 15 amp fuse to run the taillights. Checking a running light bulb socket I caused a short and now I have no tail and side marker lights. the tail light fuse did not blow but only have one power source to the taillight relay which should have 2. thanks Rich

Looking at the diagram there must be a break in one of the wires between connector 1F and the relay, possibly at the splice point which the dot indicated in the diagram, these are usually soldered and insulated. Maybe you can remove the junction block and locate the splice point by removing some insulation from the wires. The relay contacts are numbered 1-4 with 1 and 2 being hot all the time, 3 goes to the switch and 4 goes to the fuse and back to the tail lights, remove the relay and see if the terminals are marked on the bottom. But the problem is still that there is no voltage to one terminal and if both terminals should have voltage from that splice point then that is where the open circuit is.

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Ted Ritter


I have more than 28 years experience as toyota technician, I will be able to answer most questions related to the Toyota product line up to the present year models,I am located in the US but welcome questions from other regions of the world. When asking a question please provide specific information: year,model, engine,transmission information. Provide as much information as possible including a brief repair history if possible. I have been a volunteer here for more ten years an have answered over 16,000 questions helping Toyota owners with their problems and save thousands of dollars without any compensation, some of my answers are published on many other websites including google and various automotive forums. DONATIONS ARE VERY MUCH APPRECIATED, IF YOU HAVE RECIEVED HELPFUL INFORMATION PLEASE MAKE A DONATION. AS OF TODAY (JULY 22, 2014) ALL REQUESTED GRAPHICS, ILLUSTRATIONS, DIAGRAMS, PHOTOS, WILL REQUIRE THE MINUMUM DONATION UP FRONT.


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