Ok I have some basic understand of relays but get lost. I have looked at the headlight realy wright up on this site and understand. I am looking to probly rewire a 66 ford truck using an aftermarket universal kit at some point. I want to add relays where ever possible. The headlights I understand. Here is a list I would like to add relays too:
Heater(basic 2 speed High and Low)
Turn signals
Stop light
radio
Dome Light?
Dash Lights?
Switched under dash lights(not orginal)
Underhood light


I dont quite undertand how to wire these systems up using relays. Can I use the same relay for the high and low function of the heater or one for each?

I thought I would buy a junction block and then run a hot from the battery to the block and then from the block to a fuse panel. that way i can keep all the relay wiring neat and concise. Is there any problem with this? Should the hot for the junction block come from the battery or the alt, or the starter relay? or is it ok on any of those? I was also thinking of adding a stud with a nut so all my grounds are together as well. maybe simular to the block for the hot of the relays.

If some one could provide a diagram for each that would be great. Or anymore information on the way I am thinking of setting up the wiring with the blocks. I do want it to be so that everything is off when the switch is off. Also if you can think of anyother systems i can add a relay too you can include that as well. If one of the systems I have mentioned should not be relayed please let me know. Thanks

Note: I do plan to use stock switches by taking the plastic conectors off the old harness and putting new ends on the new wires and sodiering them together. Also would any of this change if i went to a toggle switch system and had the switch for power, and acc. and then a push button for the starter?? I am unshrue at this time which way I want to take the truck. Thanks

One last thing. I may not put the delay wipers in and just keep them a 2 speed. If i did this i take it i would wire up the wipers the same as the heater? If i kept the delay wipers any way to put a realy to them as well? thanks

 

Why do you want to add a relay everywhere? A relay is used when you want to open or close a circuit of one form (different frequency, heavier current, etc) through a control circuit of another form. The only other times you would need it would be to provide isolation or to reduce the arcing on a switch controlling an inductive load.

I couldn't imagine a truck with a relay for every circuit you just described. It would be costly, messy, unreliable, and a pain to wire up. Keep it simple -- that's always the best policy.

Now, if you're going to be running things like bigger headlights and tail lights \ trailer lights that will need to pull a lot more current than the stock wiring harness can handle, then yes you would use a relay. But things like the dash lights, under-hood light, radio, etc. aren't usually controlled by a relay. My advice would be to look at what kind of electrical loads you're wanting to put on those circuits you described. Once you've figured out what you really need in the end, then we can get a better idea of where a relay really is needed and where it's not.

 

Well I am thinking of adding reverse lights and tralier hook up. So would I need a relay for those? also how about the heater and forget the rest. thanks

 

I don't see a use for a relay in reverse lights. Reverse lights are usually run from a hot-in-run wire, through the backup switch on the transmission, then out to the reverse lights. Unless the reverse lights were part of a trailer wiring assembly, then it's possible. Again, it just depends how much current you're wanting to pull with a trailer hooked up.

Why do you want to add a relay to the heater? Usually the blower motor for the heater is sourced through a breaker on the fuse panel, then through the blower motor resistors and finally a speed switch. It's interesting though, my friend and I were working on his Escort a while back and we found that the blower motor was ran off of a relay. My guess for it being done this way would be to ease up the arcing on the switch when you shut the heater off. On my old Galaxie, the original heater switch was torn up pretty bad from arcing. The blower motor is wired directly to the speed switch, through the blower motor resistors. When you shut the switch off, the current in the inductive blower motor wants to keep flowing and arcs across the contacts. But it lasted 30 years that way, so I guess I can't complain too much. If yours is working the way it is then I would just leave it. "If it ain't broke, don't fix it."

 

One possible reason for this relay is to keep the A/C coil in the dash from freezing up. On some of the older systems, when the A/C was on, the relay would keep the fan on low, making it impossible for the driver to shut the fan completely off in A/C mode. If there was no airflow through the A/C coil whe the A/C was running, it would freeze up into a block of ice.

I agree, I would forget the relay ideas. This is not a case of whats good for one circuit, must be good for everything. Relays have there place, but only in certain circumstances.

I would buy an aftermarket universal harness, modify the switches like you mentioned, and follow the instructions that come with the harness.