As originally wired, the headlights would blink after the truck had been running for an hour or so. Based on feedback from the forum and after doing all the easy stuff to try and solve the problem, I decided I was going to add relays to the headlights and after market fog lights. Last night, I took a stab at the fog lights. Unfortunately, it was clear something was wrong. As soon as I connected the positive battery terminal, one fog light was always on. Once I turned on the headlight switch, it would switch to the other fog light (passenger to driver) but would switch back when the high beams were on or the headlight switch was off. When tested with a volt meter, the 87A terminal was always drawing 12 volts and the switch terminal that was wired into the low beams was not registering on the meter/ getting an error. A diagram of the relay wiring circuit could can be found below. Any idea on how to solve this problem?



As for the headlights, that seems even more complicated. By my count, I would need four, one device relays! As you can see from the [terrible] diagram below, there is an individual feed to both headlights that originates inside the cab. I do believe the individual feeds splice together under the dash before they go into the headlight switch but it is a rats nest of wires. Am I correct in my assessment that I will need to install 4 individual, one device relays in the engine bay (2 for the low beams, 2 for the high beams)? Or should I cap off one feed from the cab and just use a dual device relay off a single circuit for each headlight?




Thanks for any and all help. Please forgive the awful MS-Paint diagrams and feel free to ask any clarifying questions.

 

This may help you

 

87 and 87a are the N/O and N/C contacts, so that is why they will flash back and forth as you power/unpower the relay. You need to tie BOTH lights together and hook them to one point of the relay.

You need THREE relays to make everything work properly. TWO for the lo/hi beams and ONE for the foglights.

Here is headlight relay diagram:




This is the diagram for the fog light relay:
(the 87 terminal will include BOTH fog light bulb wires)



The 86 terminal comes from a switch on the dash. In this diagram it only comes on with the low beams(or high beams depending).

 

Freightrain- Thanks for your continued guidance. Just to clarify, I will be tying the lights together so they contact to the relay with one wire? Also, for the headlights, I will only need to use of of the two wires individuals wires for the high beam and low beam? And will just cap off the unused wire? Thanks again.

 

I think your issue is you're using a "changeover" relay.

 

HIO Silver- What type of relay should I be using? Single device/ four prong? The ones I am using are multi device/ five prong.

 

This is a changeover relay:



You need a double output relay:



Or a dual contact relay:



Or a four-pin "make or beak" relay where you split the output of terminal 87.

 

I think you are right Hio.

All three relays should be Bosch "30 amp" 4 pole relays. Not a 5 pole relay. On a 5 pole relay, power from #30 is connected to #87a when the relay is at rest. And from #30 to #87 when the relay is energized. You don't need #87a.