automotive relays

[zzebby]

Just finishing off a project and putting in the relays and notice that I see relays used a lot and yet little or no fuses.   Do see a lot of fuseable links but
Do the auto relays have built in fuses and if you pop one then you just replace the relay?  Most relays are rated for 25  or 30 amps  so if you exceed that in a short does it burn open the contacts or ? Am using the GM type D4227 is one set of numbers and 12088567    D00   are the other numbers.  They are rectangular relays about 5/8  x  7/8  by 1 inch high  with just 4 contacts.  What is the amp rating of this one?

[kb426]

I put fuses in line going to the relay. I bought a mess of the Bosch style on ebay.

[enjenjo]

There is no fuse in the relay. I fuse  the control circuit, and use a beaker on the load circuit.

It might pay to mention types of fuses and  breakers here. Fuses for the most part, come in two types. Normal, and slow blow. you would want a slow blow fuse where you have a high initial load, which quickly drops to a lower load. Glass fuses blow slower that ATO/ATC fuses. Computers normally use a fast blow fuse. Heater blowers, and other motors, use slow blow fuses, unless you are using a relay.

Breakers come in several types, fast blow, slow blow, self reset, and manual reset. If the circuit you are protecting would be damaged if energised suddenly, use a manual reset breaker. Something like power windows with a momentary switch can be protected with an automatic reset breaker.

In the main power wires, I use a fusible link, or a Maxifuse. This will protect the entire system. A Maxifuse is easier to replace.

[zzebby]

There is no fuse in the relay. I fuse  the control circuit, and use a beaker on the load circuit.

It might pay to mention types of fuses and  breakers here. Fuses for the most part, come in two types. Normal, and slow blow. you would want a slow blow fuse where you have a high initial load, which quickly drops to a lower load. Glass fuses blow slower that ATO/ATC fuses. Computers normally use a fast blow fuse. Heater blowers, and other motors, use slow blow fuses, unless you are using a relay.

Breakers come in several types, fast blow, slow blow, self reset, and manual reset. If the circuit you are protecting would be damaged if energised suddenly, use a manual reset breaker. Something like power windows with a momentary switch can be protected with an automatic reset breaker.

In the main power wires, I use a fusible link, or a Maxifuse. This will protect the entire system. A Maxifuse is easier to replace.

I'm planning to use a max fuse for the main power,  but need to buy one.  The factory harness (Ford) that I've been cutting up has a 175 amp max fuse and to me that seems like waaayyy  too much.  Car would be in flames before it blew.
thanks,  will put in fuses as I already have them and the fuse box.

[38HAULR]

AAH  Circuit breakers.    I can relate an interesting story with one of these.  Some years back I had purchased a Rodded 46 Merc running a 289W.  which had previously spent most of it,s prev 6 or 7 yrs after being built, having occasional use[weddings, debutante balls].  I pressed the vehicle into everyday use,and after some usual bugs,like seized rear wheel cyls were sorted out,water pumps not  lasting due to a stock fan having it.s blades repitched to give more clearance, because the radiator was close to the engine, I figured an imbalance was chewing bearings, she ran fine after attending to these probs. One annoying prob came in ,the vehicle would die for no reason,this happened occasionally without warning ,she would shut down. whether on a highway or just around the neighbourhood, but attempting to restart in a few minutes would be fine.I checked all connections in the ignition system and main power feed over a period of months to no avail.[replaced ign sw also] One hot summers day she died sitting at a red light, would not restart and I was able to confirm loss of volts to the coil,I hot wired it,and drove home, after disconnecting my hot wire,to my dismay she started and ran,this time I got determined to find out where the supply to the coil was failing. I disconnected the coil,and fitted a load[driving lamp] to the ign sw side of the ballast resistor and switched on ign ,the lamp went out after about 10 mins,then" re illuminated" some 5 mins later. This vehicle had a shifter console that housed a bank of relays and circuit breakers,all unidentified and all wiring the same color. To cut a long story short ,I increased the load by adding another lamp and they  shut immediately , and did voltage checks on the breakers, isolated the offender. What had happened was that some clown when wiring the vehicle,had wired the ignition through a circuit breaker that fed the aircon and some other accys,the breaker was faulty as it was shutting under it,s rated load,and erratic in it,s reset. I replaced it,and immediately seperated the ignition feed from it. A lesson well learnt,but a wish to meet up with who ever wired up that vehicle in a dark alley one night still unfulfilled...........Frank