Usually the test light is connected between a test point and ground. If it lights, the test point has voltage.
to test a fuse, use the light to see if it has voltage on both sides of the fuse, checking from the terminals (one at a time) to ground. If it has voltage on both sides, it is good. If it has no voltage on either side, the circuit is not powered for some reason. Voltage on one side but not the other indicates the fuse is blown.
A relay has (in a simple case) three terminals plus ground. There is a control terminal and two power terminals. If the control terminal has voltage, then both power terminals should have voltage. (or possibly neither). If the control terminal has no voltage, then only one (or neither) power terminal will have voltage.
Hey Bill,
Ok, thanks for the explanation. I do know how to test fuses and what the results mean, but I did not know about relays…or this issue; With the ignition key in the “on” position, I tested all the fuses under the drivers side dash and got a never-seen result. Imagine there are 28 fuses, 4 rows of 7 each. The entire row to the far right are all giving no readings. Two are “open” unused, the remaining 5 wont light up my lamp, they are the HVAC blower, the perimter lights, the interior lamps (none work), the “right” exterior lamps and “left” exterior lamps. Where do I go from here? A wiring harness? I don’t have wiring schematics anyway, oh, and one of the two large-size 25 amp fuses lights up when I test it…the fuse has a light? The other 25 does not do this. Any help with this would be so appreciated
I got a new battery BTW and my driver info panel showed a 12.3 V reading just prior to starting my car. I thought I recalled the battery used to read like 12.5-12.7 before starting the car
I was confusing the two, the small metallic “boxes” under the backseat in the two fuse panels are relays. I assume they handle electronics more powerful than a 15 amp plastic fuse can deal with… I seem to remember there’s a way to lay a screwdriver across posts to test for a clicking sound, the same way you activate the starter solenoid (I do know my way around cars, but from the 80’s)
Check those fuses with the exterior lights ans A/C blower on. The fuses for those lights are powered by the lamp control module, the fuses for the lamp control module are in the right rear power distribution center.
When they refer to “exterior lights”, do they mean like your running lights, headlights etc? I didn’t know whether or not these needed to be “activated” to test for continuity, thanks. Did you see my note that one of my two 25 amp fuses (the largest amp size in the drivers kick panel, all the rest are like 10’s and 15’s) actually lights up when I probe it? It has a red glow when you probe it, what does that indicate? The other 25 lights up my probe, but the fuse itself doesn’t light up
Thanks
You need to replace the fuse that glows when you test it. It means there is internal high resistance inside the fuse and the current draw needed by the test light is lighting up the fuse. I assume you are clipping the ground lead of your probe to ground and the probing the power sources with the probe tip.
Since there is an entire row of dead fuse positions it may mean there is another larger fuse before those fuses that is bad or there is a bad connection to the bus power for those fuses. Check the 30 and 40 amp fuses for an issue.
Exterior lights are the running lights, turn signals, and license plate lights. The headlights are usually on a different circuit due to the higher power required for them.
I do not suggest you check a relay by shorting contacts unless you understand what you are doing. You may short out something if you cross the wrong connections. There is all kinds of easy to read information on the web to help you understand how relays and other things work. You should check that out.
Man, you’re good. Here’s irony, my job in the USAF was Inertial Navigation Systems of the F15-A Eagle, and practically-speaking, I can fix literally anything that requires electricity, even if I know nothing about its functionality. I’ve repaired flatscreen TV’s, Washing machines, tablets, I can strip and rebuild a laptop down to the PCBs, gaming systems, printers, every broken item I’ve ever been handed…but this …Nope! I just can’t see how the seres works in my mind. I appreciate all your help, I just can’t swing what this would cost at a shop, they want $100-$125 just to analyze the issue, not even the repair
Yeah, I knew not to arch a relay, don’t know what I was thinking. I have 10 blown discs from a bad motorcycle wreck and I take enough pain meds to put down a Bull Elephant, on my bad days I can’t focus on the simplest equations. Automotive electronics has always been outside my wheelhouse anyway, even on a less-awful day.
I will follow your instructions as you clearly do understand it, and I’ll watch Youtube vids for specifics…thank you so much for your valuable time.
You’re welcome for the help and am glad to assist along with the others here. There are some great folks here that like to help out.
I find it pretty amazing that you have worked on such sophisticated electronic systems that are in the F-15 Eagle (one of my all time favorite airplanes BTW, along with the P-38, P-51 and F-104, just to sit in the cockpit of one of those planes, totally awesome) and are stumped by automotive electrical issues and how relays operate. A little studying will get you going well. Very simple stuff. I’m sorry to hear about your pain issues and hope things get at least a little better for you.
Relays are basically just electric switches that allow a small low current (usually through a switch) to control a larger current needed for some sort of load. You don’t have to run large gauge wire to a remote switch, just to the relay and the load. The relay handles the high current, not the control switch.
One very good investment you should make is in a factory service manual for the wiring. The is no substitute for one. Ebay is a great place to get one for a very reasonable cost.
Hey Cougar,
So I heard a soft grinding noise coming from my water pump, the bearings are about to go.
My good friend who owns a Tuneup Masters will change it parts included for $250 and buying the special tool. I’ve been leaking as much as half a gallon of coolant when it sits over the weekend, now I know why. I added stopleak which lasted a month, barely a drop hit the floor, then one day it began again, I added stopleak again…worked but not as good, surely due to the pump going south. Any other work I can get done meantime with the pump out (besides a new belt). I have oil leaks at the valve cover gaskets and the oil pan, I can live with half a quart every 2 weeks.
Hey George, please see my post about my water pump going out, I can clearly hear the sound of bearings grinding at the pump/belt site, but it’s very quiet so not bad yet, I plan to have it done tomorrow, my good friend owns a Tuneup Masters and will charge me $250 which includes parts and the special tool you have to own to pull this pump. Good price yes? Dealership quoted me $1,0000
George, when I scan the car now, nothing comes up and I happen to know I have at least 2 bad O2 sensors and other stuff going on. Think my ECM is history?
Thanks my friend
$250 is definitely a reasonable fee for a water pump job. I expect you already know that the first objective in car repair for the owner is a job done correctly, and second, at a competitive price. I’ve had water pumps on my truck make weird noises but still seem to be working ok, then fail completely a short time later. So you are probably right to get it replaced. Best of luck.
Well you and Bing are kinda my Guru’s in auto repairs that are outside my skillset or prior experience GSJ. I have done a water pump. but on a '77 Z28 and an early 90’s Mustang, the Aurora with the Northstar motor complicates everything George, even plugs and wires cost $250+ because you have to pull 4 coils just to access the back 4 cylinder plugs…
That being said, I know the sound of bearings ready to seize, so far it’s quiet grinding, even my mechanic and I thought we heard a light valve tap until I looked closer.
If I didn’t tell you, I was losing half a gallon of coolant when my car simply sat for a weekend. We pulled the reservoir bottle to check leaks, nothing, I added a quality rad-stopleak and it worked perfectly for a month and then last week, back to a major leak. We could see liquid dripping from the pump when it was on the rack high up, but it didn’t look big enough to lose half a gallon in 2 days. Maybe it leaks faster while driving? Weird thing is only droplets escape when the car has been driven, in the AM the street is covered in coolant.
Hey, what else can/should I have repaired with the pump out? Will this give us better access to the radiator itself? I’ve never even seen my radiator since this is a pressurized system, the coolant fill bottle is annexed near the firewall. I am somewhat vexed because I can still clearly see the gold shiny liquid inside the fill bottle, you’d think the stopleak would no longer be inside the bottle. I think my friend was being lazy when he said it didn’t matter if we put the stopleak into the top rad hose as instructed, he said the fill bottle would be fine since it’s a pressurized system…guess we will see if the H2O pump stops my leak cold.
