Hi everybody. I have a 1997 F-150 4x4 with 5.4 / auto with factory tow package. I was towing my trailer this morning and found that I do not have running/parking lights on my trailer. I know it isnt the trailer because it works on a friends truck. I have checked all fuses associated with the trailer in the power distrobution box and the small one behind it under the hood. I can't find any blown fuses. I took a test light and a meter both out to the trailer fuse in the power dist box. It is number 1 and is a 20 amp. I have no power on either side if this fuse with the trucks parking lamps on. I also do not have power at the plug at the 7 o'clock and 11 o'clock positions. Any ideas on what to try next? I can't find which relay triggers this to try and check it. My owners manual doesnt list which relays run this. I just dont know what else to do. It is driving me nuts.

Thanks,
Chip

 

The PDB ( power dist box / engine compartment fuse panel ) Fuse #1 is hot at a times. This feeds both the trailer tow adapter parking lamps and the backup circuit.

You should have power at this fuse all the time.

I have to ask the dumb question, are you sure your ground was good when testing the fuse ?
There is nothing else between this and the battery, aside from the guts of the fuse panel.





What do you get if you pull the trailer tow parking lamp relay, and test for power using the relay socket ?



This is the half ISO relay shown in the additional relay panel on the back of the PDB.

The relay info :



You can test with pin 2 and pin3.
pin 2 is ground
pin 3 is common terminal = Fuse #1

you can also verify the ground you were using before with the ohm setting between pin #2 and what you were using, should have very low resistance.

pin #1 in the socket should have power when the truck's parking lamps are on.

If you have power at pin #3, you can jumper the pin #3 to pin #5, and you should have power at the trailer tow adapter.

The easy test ( sure you know this ) is the ground is the exposed pin in the 4 pin adapter , and the other 3 "recessed" pins are turn - park - turn, so use the center of those 3.

Let us know what happens.

 

I will double check that ground and get back to you on this. Thanks for the reply.

 

Yes, I had a bad ground for my meter and test light. I clipped it on to my hood hinge and I have power to both sides of the fuses now.

 

Okay, I have power at #3 on the relay socket, I remove #1 fuse and power goes away. I have power at #1 relay socket with trucks running lights on. I still however have only turn and brake. What next?

 

Put a jumper in the relay socket from pin #3 to pin #5 ( red line the diagram ).

This is to test the wiring itself. Check both the 7 pin and the 4 pin adapters for power on the parking lamps pin.

If it is good, then I would suspect the relay, but need to bench test it to be sure.

 

I jumped the power from 3 to 5 and still no luck on the trailer plug. Is there another connector between the engine compartment and the plug that I could have a bad connection from corrosion or something?

 

What color is the rinning/parking light wire going back to the plug?

 

Brown w/ White stripe from the diagram above.

The relay socket can be a PITA to jumper, you have to have the small male spade terminals, or file down a regular sized one to get them to fit in the socket.

If you are sure you have a good jumper in there, the next place to look for it is back by the hitch.

I have not seen a '97/'97, but I would suspect the connector to be in the same place.



Take a look, this is along the frame by the spare tire. If you are going to be testing here, it is easier to get to if you drop the spare tire.

When you tested, did you check both the 4 pin and the 7 pin adapters ?

 

mine only has a 7 pin plug. i used a pair of tweezers to jump the connection. i also replaced the relay with the one directly beside it. still no power at the plug

 

If you are sure you got a good jumper across the pins, next is to see if you have that connector by the frame, and check for power there.

 

It about 32 deg outside. I only have a carport so i will wait until tomorrow after work. I am going to drop the spare tire and check at that connector. I took the trailer plug apart and it looks like new. The weather cover on it kept it in nice shape inside. I also have another proble with my truck. Is the voltmeter a printed circuit? My voltmeter has been jumping around for a while. It did this years ago. I replaced a bad alternator and it seemed to quit. Every time I use the emergency brake and release it, it screws up the voltmeter. I know I have a lose connection but for the longest while it wasnt even working. Now today I used the parking brake and it started working again. I used to be able to hit the dash and have it stop jumping around. Today I did that and it quit working again. If it is a printed circuit I know it is shot. Can I just replace the voltmeter or is it all one big asemble included with the rest of the dash display?

 

The Trailer tow adapter plugs into the factory harness by the spare tire on the 1997, same as the 99+



You are looking for the Brown w/ White Stripe wire



This way you can test from the trailer tow adapter to this connector ( ohms ) and then from the front to this connector for power, or if you have some wire, put on a small male crimp, and install it into pin #5 in the relay socket.

Even though the swap showed no change, might be best to bench test the relay, and make sure it is OK.
Ohm meter from pin #1 to Pin #2, should show 82 to 100 Ohms of resistance

Next Ohm meter the pins #3 and #5. Without power should show infinity for ohms, and then apply power to pins #1 & #2, and the meter should show no / low ( ~ 5 ) ohms.

this would confirm the operating state of the relay.

 

You can pull the cluster and take a look at the back in that area for a cold solder joint that finally gave up.

The other part of pulling the cluster, is to reseat the connectors on the back of it.

If there is a problem with the volt meter, that is actually built into the cluster electronics.

 

I will be working on the wiring over the weekend. Weather has been bad here and all I have is a carport. I will let you know how I make out. Thanks for all of your help.