If there are 4 relay terminals and they are
labeled 30,85,86 and 87 then it is a normal SPST "Bosch" type relay. The Radio Shack part mentioned above (#275-226, $5.99) will work in this case.
Not all "Bosch" relays are created equal. The Radio Shack unit is rated for 30 Amps. Some of this type are rated for 40 amps.
Incandescent lamps are especially hard on relays because their cold turn-on current peaks at around 10 times their running current. This means about 250 amps peak current to turn on your lights that normally draw only 25 amps.
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