What's the most accurate way to check a Ranger's brake light sockets with a ohm meter

greaseyfingers · Oct 14, 2013

What is the best way to check a Ranger's brake light bulb sockets with a ohm meter

I'd like to check my Ranger's brake light sockets and front turn signal sockets with a ohm meter, if someone can explain the best way for doing so..

Is there also a procedure for checking the turn signal switch using a ohm meter..

RonD · Oct 15, 2013

An OHM meter checks the resistance or lack of resistance in a wire or circuit.

0 ohms means no resistance, so a good wire or a shorted wire depending on what you are testing.

When you touch the two Probes together you should get 0 ohms, that tests the ohm meter.
Set OHM Meter on lowest setting, usually 200
There is no + or - when testing OHMs so color of the probe doesn't matter

Some digital OHM Meter show N/C when switched to OHMs which means No Connection, touch Probes together and it should change to 0 ohms.

Take a light bulb and test with one probe on the ground and one probe on the power contact, good bulb will be 0 ohms, on dual filament bulbs(brake and tail light) check both contacts.
In the socket there is a 12v contact and a ground contact, put one probe on ground, this is usually the metal sleeve the bulb slides into but can be one of the contacts, and put other probe on a frame ground, should show 0 OHMs if ground is good.
Also put 1 probe on ground and 1 probe on 12v, there should be high ohms or N/C, this means there is no short in the wires.
Common place for shorts in tail lights is the trailer connection.

The 12volt contact can be tested by switching to DC Volt meter and testing for 12v when light switch is on, but you can test OHMs with a long wire.
OHMs test:
Remove Positive and Negative battery cables from battery
Connect long wire to Positive cable, not battery.
Turn on Light switch(this test only works if the are no Relays in the light circuit)
Take other end of long wire to bulb socket
Test OHMs between long wire and running light 12v contact in bulb socket, should be low or 0 ohms.
Press down brake pedal and check OHMs on that bulb contact, should be low or 0 ohms

The turn signal part(contact) can only be tested with battery connected using a 12v meter

greaseyfingers · Oct 15, 2013

RonD said:
An OHM meter checks the resistance or lack of resistance in a wire or circuit.

0 ohms means no resistance, so a good wire or a shorted wire depending on what you are testing.

When you touch the two Probes together you should get 0 ohms, that tests the ohm meter.
Set OHM Meter on lowest setting, usually 200
There is no + or - when testing OHMs so color of the probe doesn't matter

Some digital OHM Meter show N/C when switched to OHMs which means No Connection, touch Probes together and it should change to 0 ohms.

Take a light bulb and test with one probe on the ground and one probe on the power contact, good bulb will be 0 ohms, on dual filament bulbs(brake and tail light) check both contacts.
In the socket there is a 12v contact and a ground contact, put one probe on ground, this is usually the metal sleeve the bulb slides into but can be one of the contacts, and put other probe on a frame ground, should show 0 OHMs if ground is good.
Also put 1 probe on ground and 1 probe on 12v, there should be high ohms or N/C, this means there is no short in the wires.
Common place for shorts in tail lights is the trailer connection.

The 12volt contact can be tested by switching to DC Volt meter and testing for 12v when light switch is on, but you can test OHMs with a long wire.
OHMs test:
Remove Positive and Negative battery cables from battery
Connect long wire to Positive cable, not battery.
Turn on Light switch(this test only works if the are no Relays in the light circuit)
Take other end of long wire to bulb socket
Test OHMs between long wire and running light 12v contact in bulb socket, should be low or 0 ohms.
Press down brake pedal and check OHMs on that bulb contact, should be low or 0 ohms

The turn signal part(contact) can only be tested with battery connected using a 12v meter

Before receiving your information..

I tested my 1990 Ranger's passenger side front turn signal socket with the ohm meter's probe on the ground inside the socket and probed one of socket's power terminals, I got less than 1 ohm..

When I tested the passenger side front turn signal socket with the ohm meter's probe on the ground inside the socket and probed the socket's second power terminal, I got 5.2 ohms..

When I probed both the power terminals inside the passenger side front turn signal socket, at the same time, I got 5.2 ohms..

After using the same test procedure on the driver's side front turn signal socket, the results were almost the same, except I got 5.4 ohms, instead, on testing the same terminals on this turn signal socket, as when I tested the other one..

The ohm meter test results were the same on both front turn signal sockets, whether the turn signal switch wiring harness connectors were connected, or disconnected from the turn signal switch..

Would this indicate that the both my 90 Ranger's front turn signal sockets are bad, or does it indicate something else..

And could this be causing both my Ranger's rear turn signal lights to flash, at the same time, when I use the right turn signal switch..

RonD · Oct 15, 2013

Usually when you have two lights flashing when only one should be it means the ground on the light that should be the only one flashing is bad or has high resistance.

Does just the wrong tail light flash or does the indicator in the dash for that light flash as well?
If only the correct indicator light flashes then problem will be in the tail light system not multi-switch, usually trailer connectors.

What scale were you using on the OHM meter?

less than 1 ohm is a short
You can pull the flashers out and repeat test
Also with key off, turn on turn signals, the arm, and test also same test with light switch on and off.

If you have an alarm/locking system, keyless entry type, those can through a twist into the readings because they often "flash" the lights for lock/unlock so are part of that system now.

greaseyfingers · Oct 15, 2013

For some unknown reason using the right turn signal switch causes both rear turn signal lights to flash, while the front turn signal is flashing on the passenger side, like it's suppose to and the dash light indicator works correctly for the right side..

The scale for using the OHM meter was set at 200 when did the testing

I got the same results testing for OHMs when the the turn signal flasher, emergency flasher, and turn signal switch were installed, and removed..

RonD · Oct 15, 2013

I would check the ground on the Right rear turn signal.

When you remove the bulb on the Right rear and turn on the signal does the left rear bulb still flash?

Often that ground wire is Spliced to the frame ground wire for the Left rear.

If that splice gets corroded then resistance goes up.
The Left Rear bulb is usually the next best ground via the brake light circuit, to get that ground it has to pass thru the bulb which makes that bulb flash as well.

greaseyfingers · Oct 15, 2013

RonD said:
I would check the ground on the Right rear turn signal.

When you remove the bulb on the Right rear turn signal socket and turned on the signal switch does the left rear bulb still flash?

Often that ground wire is Spliced to the frame ground wire for the Left rear.

If that splice gets corroded then resistance goes up.
The Left Rear bulb is usually the next best ground via the brake light circuit, to get that ground it has to pass thru the bulb which makes that bulb flash as well.

When I removed the bulb on the Right rear turn signal socket and turned on the right turn signal switch, the left rear bulb still flashes..

I even tried running a temporary ground wire from the negative battery post to the right rear turn signal, and both rear turn signal lights still flash..

I also cut off the right rear 3 wire turn signal socket and the left rear turn signal light still flashes..

When I put on the brakes, when the ignition switch is on, the rear turn signal lights will stop flashing and the right front turn signal light will stop flashing for as long as I'm depressing the brake pedal..

Even when the ignition switch is turned off, the passenger side front turn signal will light up, when the right turn signal switch is on and the brake pedal is being depressed..

I'm almost temped to cut off the front passenger side front turn signal socket, in case it's a bad socket, and see if that's the cause of my rear turn signals not working properly..

RonD · Oct 15, 2013

greaseyfingers said:
When I removed the bulb on the Right rear turn signal socket and turned on the right turn signal switch, the left rear bulb still flashes..

I even tried running a temporary ground wire from the negative battery post to the right rear turn signal, and both rear turn signal lights still flash..

I also cut off the right rear 3 wire turn signal socket and the left rear turn signal light still flashes..

When I put on the brakes, when the ignition switch is on, the rear turn signal lights will stop flashing and the right front turn signal light will stop flashing for as long as I'm depressing the brake pedal..

Even when the ignition switch is turned off, the passenger side front turn signal will light up, when the right turn signal switch is on and the brake pedal is being depressed..

I'm almost temped to cut off the front passenger side front turn signal socket, in case it's a bad socket, and see if that's the cause of my rear turn signals not working properly..

The I would check the multi-switch.

You can start at the back and remove both bulbs, use OHM meter between the two turn signal contacts with key off turn signal off.
Should be high ohms,
if not then either the wires or multi-switch has a short between these wires, disconnect multi-switch plug and test again, if short goes away then replace multi-switch.
If short is still there with multi switch disconnected then you need to start tracing the wires, start at the back and work you way forward, unplug any connectors and retest as you go.

If there was high OHMs on the first test then turn muli-switch to right hand turn, key off
test OHMs again if ohms are low then replace multi-switch.

You haven't said yet if you have a trailer light connector, these are often the source of these type of issues.

greaseyfingers · Oct 15, 2013

RonD said:
The I would check the multi-switch.

You can start at the back and remove both bulbs, use OHM meter between the two turn signal contacts with key off turn signal off.
Should be high ohms,
if not then either the wires or multi-switch has a short between these wires, disconnect multi-switch plug and test again, if short goes away then replace multi-switch.
If short is still there with multi switch disconnected then you need to start tracing the wires, start at the back and work you way forward, unplug any connectors and retest as you go.

If there was high OHMs on the first test then turn muli-switch to right hand turn, key off
test OHMs again if ohms are low then replace multi-switch.

You haven't said yet if you have a trailer light connector, these are often the source of these type of issues.

There is no trailer light connector on my 90 Ranger..

I've already tried using a good working turn signal switch from my 89 Ranger and put in my 90 Ranger to see if that would correct the issue of both rear turn signals blinking in my 90 Ranger, but it didn't help..

I also tried removing the bulb on the Right front and Right rear turn signal socket and turned on the right turn signal switch, and the left rear turn signal bulb still flashes..

I even tried running a temporary ground wire from the negative battery post to the right rear turn signal light bulb socket when the bulb was installed, and both rear turn signal lights still flash..

I also cut off the right rear 3 wire turn signal socket and the left rear turn signal light still flashes..

When I put on the brakes, when the ignition switch is on, the rear turn signal lights will stop flashing and the right front turn signal light will stop flashing for as long as I'm depressing the brake pedal..

Even when the ignition switch is turned off, the passenger side front turn signal will light up, when the right turn signal switch is on, for as long as the brake pedal is being depressed..

I'm almost temped to cut off the passenger side front turn signal socket, (in case it's a bad socket), and see if that's the cause of my rear turn signals not working properly.

After doing some online searches for trying to find out the possible causes of both rear turn signals blinking on a vehicle..

I discovered that one possible cause for this happening, according to some peoples' experiences with this problem, is when a front turn signal bulb socket is shorting out, it can cause both rear turn signal lights to flash..

Does that sound possible?

RonD · Oct 16, 2013

This is the wiring diagram for the turn signals
http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_turn_stop_hazard.JPG

It shows the only common connecting between front and back is in the multi-switch.

The Parking(running) lights have a common connection at the light switch, could the Parking light be flashing and not the turn signal light?
I am assuming it's a double filament bulb/socket

greaseyfingers · Oct 16, 2013

RonD said:
This is the wiring diagram for the turn signals
http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_turn_stop_hazard.JPG

It shows the only common connecting between front and back is in the multi-switch.

The Parking(running) lights have a common connection at the light switch, could the Parking light be flashing and not the turn signal light?
I am assuming it's a double filament bulb/socket

According to as you said, "It shows the only common connecting between front and back is in the multi-switch."

Even when the ignition switch is turned off, the passenger side front turn signal will light up, along with the brake lights, when the right turn signal switch is on, for as long as the brake pedal is being depressed..

When the ignition switch is turned off, as mentioned, it doesn't make any logical sense how any electrical power could be getting to the passenger side front turn signal light that will light up, along with the brake lights, when the right turn signal switch is on, for as long as the brake pedal is being depressed..

I noticed that one of the wires going to the brake light switch looks like it has been badly kinked, at one time, that's about 6 inches from the brake light switch..

Is it possible that if the copper wire was severed enough under the wire's insulation, going to the brake light switch, so that maybe the copper wire wouldn't be able to carry it's required electrical load for completing the brake light circuit, as it should..

Could that potentially send the electrical power else where, in trying to do so, and cause the electrical problems my 90 Ranger is having..

My Ranger's brake lights seem to be nice and bright, so even though one of the brake light switch wires looks badly kinked, I assumed it was still doing it's intended function..

Or, should I resplice it anyway, and see if removing that bad kink makes a difference, in case the copper wire has been partially severed on the inside, that can't be seen because of the wire's insulation..

RonD · Oct 16, 2013

Brake light switch has power 24/7(all the time), as do parking lights via the light switch.

It reads like the brake light power is being transfer to another circuit via a short, since all the parking lights share the same circuit applying power to one should light up the others, and since the brake light and signal light are the same circuit(wire) then the same applies, short to one means short to all.

The brake light switch sends power to the multi-switch from what I see on the diagram, BUT a short between the brake light/turn signal wire and parking light wire anywhere on the wires running to the rear would present you with front parking lights coming on when brake lights were on or when flashers were on.

I don't think the kink in the wire would cause this but cutting it out wouldn't be a bad idea for future issue.

greaseyfingers · Dec 9, 2013

RonD said:
This is the wiring diagram for the turn signals
http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_turn_stop_hazard.JPG

It shows the only common connecting between front and back is in the multi-switch.

The Parking(running) lights have a common connection at the light switch, could the Parking light be flashing and not the turn signal light?
I am assuming it's a double filament bulb/socket

It uses a 1157 double element bulb in the socket and it isn't the parking light element that flashes..

When I put on the brakes, when the ignition switch is on, both the rear turn signal lights will stop flashing and the right front turn signal light will keep flashing while I'm depressing the brake pedal..

Even when the ignition switch is turned off, the passenger side front turn signal will light up, when the right turn signal switch is on, for as long as the brake pedal is being depressed..

I'm almost temped to cut off the passenger side front turn signal socket, (in case it's a bad socket), and see if that's the cause of making both of my rear turn signals to flash, at the same time, whenever the right turn signal is being used.

After doing some online searches for trying to find out the possible causes of both rear turn signals blinking on a vehicle..

I discovered that a possible cause for this happening, according to some people's experiences with their vehicle's both rear turn signals flashing, at the same time, is when a front turn signal's bulb socket is shorting out, it can cause both rear turn signal lights to flash..

Does that sound possible?

Or, do you have any other better ideas to check that might be causing this problem?

kimcrwbr1 · Dec 10, 2013

Do you have a trailer light adaptor in the connection at the rear of your truck i9f so pull the adaptor out clean the connections and use dielecrric grease to put them together without the adaptor and see how the lights work?

kimcrwbr1 · Dec 10, 2013

I never really understood how it actually works but with your brakes on the turn signal flasher turns the brake light off and on on the side your turning.

What's the most accurate way to check a Ranger's brake light sockets with a ohm meter

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