1994 Class A chassis electrical issue

[bullfrog]

Did you remove the bulb? Do so and if your multimeter doesn't automatically adjust the scale lower the scale down and see if you get a reading. Usually you are looking for continuity and won't be measuring anything over 2k ohms but just start lowering the scale and see if you get a reading. Another way to get an idea of how many ohms there should be is to take a new piece of wire a few feet long and strip the insulation off either end and put the red lead on one end and the black lead on the other. You will probably have to select the lowest scale especially if 200 ohms is the lowest to get a reading. Very seldom will you use the 20k scale as you can get a reading there most likely holding both probes between two wet fingers. The main thing you are concerned with is how well the light is grounded to the frame so find or create a spot on the frame that is shinny metal that you can connect your black lead to. Then connect the red lead with the power off the circuit (key off and no one pushing the brake petal) to the ground terminal in the bulb socket which is usually connected to a black wire. The meter should read o on the 2k scale or maybe a few ohms on the 200 ohms scale but not much more than you read on the new piece of wire when you checked it. Then move the red lead to the positive terminal and see what you get and if on the lowest scale it reads the same as the black one did it is probably shorted, in other words connected to ground and it shouldn't be but until you verify all the ground points with the ohm meter on the lower scale all bets are off as back feeds are one of the most difficult problems to find and fix. Bad ground connections can look perfectly fine but the meter doesn't usually lie if it reads infinite wiggle the wire or rotate the connection if it reads lower or 0 remove and clean the connections and check for a bad terminal or broken wires at the connection. Make sure everything is tight when you are done. Let us know what you find as I said you probably have more than one problem.

 

[Rhianntp]

Should there be 0 reading between the red and black wires going to the socket?

 

[Rhianntp]

My meter has a continuity setting with noise.. should I use that instead?

 

[bullfrog]

You can use the noise setting but it sometimes will miss lead you if you don't check reading on the lowest scale and compare it to what a new piece of wire reads (usually 0 or a few ohms depending on the quality of your meter). Check the ground to the frame first as the running lights use several bulbs and grounding points it can miss lead you. Once you have checked the negative terminal move the red lead to the positive terminal and if it reads 0 on the lowest scale then that means the positive wire has shorted to ground (connected) and should have blown a fuse if it had one or bare wire touching the frame or grounded socket somewhere. Usually without a fuse the wire overheats and burns.

 

[bullfrog]

If use too high of a scale the meter will read zero because the tolerance level for that scale is higher than the reading. If you use too low a scale it will max out because that scale cannot read above the stated amount. Using a scale that gives you a mid range reading is best. Some meters are self adjusting, some are analog and most today are digital, it depends on what meter you have.

 

[Rhianntp]

This meter is a Sperry DM-6400

 

[highdesertranger]

check like I told you, for continuity from a known good ground(frame) and the black wire that should read 0 or real close to it. the reading you get across both wire on the same socket will vary depending on how it's wired from the factory. If there is another bulb or other resistive element it will read that. FYI a bulb will read about 2.5. Then check for 12v when the light should be lit like when the brake is applied.

Also you never gave an answer on how many wires you have off the large terminal on the starter.

Highdesertranger

 

[Rhianntp]

Some new info:

Both the positive and negative wire for the disconnected license plate light have near zero ohms and set off the continuity noise 

One of the two pos contacts inside each rear brake/ turn light have same result

3rd brake light socket appears normal

 

[bullfrog]

With that meter you can use either continuity or ohm meter as long as you insure there is no voltage on the circuit. You can do that with the 12 volt DC function of the meter before turning to the continuity or ohm meter function. The problem with a back feeding circuit is that when you apply power to the brake light circuit by pushing the brake petal it can not reach the frame to get to the battery so it tries to travel through the tail light or turn signal circuit. If you have side marker turn signals and a third brake light it get even more complicated. The more bulbs the more grounds often grounded to the frame by a common bolt which when it looses connection with the frame still allows power sometimes to travel backwards( this is a simplification of what really happens) through the other circuits bulbs to one of their other connections to one of their other grounds.

 

[Rhianntp]

check like I told you,  for continuity from a known good ground(frame) and the black wire that should read 0 or real close to it.  the reading you get across both wire on the same socket will vary depending on how it's wired from the factory.  If there is another bulb or other resistive element it will read that.  FYI a bulb will read about 2.5.  Then check for 12v when the light should be lit like when the brake is applied.

Also you never gave an answer on how many wires you have off the large terminal on the starter.

Highdesertranger

Here is what the starter situation looks like

 

[bullfrog]

The same thing happens when you turn on the running lights or have the turn signals on. Your meter's continuity tester will sound when it senses less than 100 ohms which is more than any connection you will be testing should have, It is easier than watching the meter and if you doubt it just check the ohm function reading. It is also a good way to insure you have the leads connected properly, just touch the two leads together and it should sound with the meter on the continuity function.

 

[Rhianntp]

Does the info from post #48 a few min ago help us at all?

 

[bullfrog]

Nope, as HDR an I both said check continuity from the negative terminal of the bulb socket with the red probe to the ground on the frame by finding or cleaning a shiny spot of metal on the actual frame and touch with the black probe there. The meter should sound if there is continuity as there should be.

 

[Rhianntp]

What I posted there was the results of that...also inside the trailer harness the found prong sounds, but so does the prong labelled running lights ( green)

 

[Rhianntp]

I took a small grinder drill tip and cleaned off all the rust to bare metal...clipped a small jumper cable like wire to that spot then clip the neg lead from the meter to that... Then use the POS probe to check things... Post #48 was the result

 

[highdesertranger]

Ok It didn't sound like that in your other post. the hot wire should not read 0 to the frame.

The smaller of the 2 wires on the large terminal on the starter is a fuse link, check it. My guess is it splits to two fuse links above the picture somewhere.

Highdesertranger

 

[bullfrog]

Alright so you did what we instructed you to do one lead on the bulb socket and one on the frame and got continuity right? If so then set the meter to measure 12 volts DC and move the red probe to the positive terminal of the bulb socket and leave the black lead attached or touching the frame and turn on the running lights. You should read 12 volts. If so when you reinstall the bulb I should light. If no voltage let us know what running lights did light if any.

 

[Rhianntp]

One of the prongs inside each socket reads 11.52 volts and doesn't light up a bulb

 

[bullfrog]

Sorry to be so slow to respond. So you have no power to any of the running lights, right? if so and the meter says the positive wire is connected to ground that is a short. A short would result in a melted or burned wire without a fuse in the circuit, if no burned wires there must be a blown fuse and still a short that the fuse prevented damaging the wire in the running light circuit. Many times a marker light will get water in it and rust which will short out the circuit I would pull all the covers and check all the sockets and bulbs for rust deposits then follow the power wire from the license plate socket to where it probably goes to the tail lights, trailer pigtail, marker light and front running lights looking for rubbed or melted insulation, uninsulated connections anywhere it could come into contact with a ground because it apparently has. Once you get to where it enters the inside you should end up at the fuse block and a running/tail light fuse. I would also insure the battery ground wire is well connected and clean where it connects to the frame. Now on to the third brake light using the frame ground do the same checks as you did with the license plate light but check for power with someone applying the brake and let us know what you get.

 

[bullfrog]

Okay time lag here your post #58 which sockets are you testing? If you have power a good bulb and a good ground in a complete circuit it will light.