OK, I have a dumb question! When I add relays for say the wipers or starter or what ever, do the primary (original) relays stay, and what is their purpose?
The relays you have so far installed don't replace any relays that were in the car.
These cars run few relays as most of the electricity to elements that use it runs through a switch, for example the ignition switch provides power to a set of circuits that provide power to a switch and then to the element, such as the wiper motor. The primary circuits on all Xs that use a relay are: headlight lifting and lowering; rear defrost; horn; cooling fan; some interlocks such as key in the ignition chime or in the distant past an ignition interlock with the seat belts. As more features were added they added more relays such as the double relay for the injection system, interior lighting relay to provide time delay and on the last few years a high beam relay. There are likely a few more that my addled mind isn't recalling at the moment but you get the gist.
The point of a relay is to take the load off the contacts in switches due to the high amperage load they are switching, which can melt the switch as they age due to increases in resistance from arcing, dirt and corrosion. Relays are also used to automate actions such as the headlight motor's motion when you turn on the lights. Relays can also be used to provide more power to an element than a switch can offer, or at least an old somewhat corroded one
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Due to the age and relative lack of certain quality replacement parts, many will put in relays to save the switches from destruction due to heat from the above mentioned reasons. Good candidates are the ignition: switch loads for powering sub circuits and the starter; headlight switch, due to the high amperage going through them naturally during use; and then things like wipers. Doing this can provide longer life to the switch and in many cases substantially better performance of the element being powered as there is less power loss and the relay can be mounted close to the element using the power. Relays are pretty damn cheap and if one fails it is cheap and easy to replace.
So a lot of positives, there is also a notable negative: complexity. You have changed the systems so now the wiring diagram is no longer accurate. You have added more parts and connections, all of which can fail and make trouble shooting that much more difficult. You are adding weight in wiring, relays and mounting brackets/boxes, subtle I know but things like this do add up.
Personally I am a strong advocate of adding relays. If you do your work well with quality connectors, crimping tools, secondary insulation, carefully locate the new parts and install them well they will make the car more reliable. Additionally, changing the system so that the things you add can be removed and the car returned to its orignal state if desired in the future. You don't want to cut out perfectly good parts of the wiring system as it is quite high quality, actually does work well and you don't want to be the PO. As in: "What the F--- was the G-- d---- Previous Owner thinking when he did that to this otherwise fine car!"
However. If you don't follow basic rules you could burn the car down which is terribly bad form, so any line coming from the battery needs to have a fuse in it, preferably before the relay and preferably close to the battery so any vagrant voltage due to errors, damage or what have you won't start a fire.
So relay away...
