So you've upgraded your wiring for your headlights, fog lights, auxiliary lights, and you're driving along and suddenly it's dark - one of your relays has failed. (This has actually happened to me - failed low beam relay at zero-dark-hundred in the morning.) So you move them around so the failed relay is running some non-mission-critical function like your driving lights or something like that, but you'd like to get everything back to tip-top shape. You know that going to the parts store and asking for a "Hella SPDT ISO mini relay" is going to be futile... well... I was in that situation earlier today, not because one had failed, but because I needed a relay to make my fog lights work properly due to the factory wiring in my Jeep using the high beam filaments as ground for the fog light control relay. It actually makes sense, you take power from the parking lamps, switch that with the dash fog lamp switch to the relay coil, and then ground the other end of the relay coil through the high beam filament, then everything operates legally and you need only one relay. Unless, of course, you've abandoned the factory headlight wiring and are using a relay harness (in which case your brights will latch on the first time you use them, not good), or you're using LED headlamps (I suspect in this case the fogs would just not work at all). So I needed a SPDT mini relay (because I had sockets for them, but the only relays I had in my junk box were SPST dual 87 terminal relays, which are what was used for my added on headlight wiring.) What I needed to do was to intercept the wiring between the high beam and the fog light relay, snip it, connect the headlight end to 86 (coil +12V), fog light relay coil end to 87a (NC), and connect both 30 (common) and 85 (coil 0V) to chassis ground. Additionally, this'll be useful if I ever add driving lights as then I can connect the 85 of the future driving light relay to the currently unused 87 (NO) terminal of this relay, then they'll only come on with the high beams and will automatically shut off if I have to dim my lights for oncoming traffic.
So anyway, while tracing out the wiring so I knew which wire to snip, I had to look in the relay box under the hood... some of the relays used from the factory were all the exact relay I needed!
So, if you need a ISO mini SPDT relay (with 87 and 87a terminals, or in other words NO and NC relative to 30) ask for a fuel pump or cooling fan relay for a 1999 Jeep Cherokee.
If you need a ISO *micro* SPDT relay, ask for a fog light relay for the same vehicle.
I didn't see any dual-87-terminal relays used under there so I still don't know the magic words to ask for one of those.
hope this helps someone, it did me! (my fog lights are now legal and I didn't have to wait for anything mail-order)
So anyway, while tracing out the wiring so I knew which wire to snip, I had to look in the relay box under the hood... some of the relays used from the factory were all the exact relay I needed!
So, if you need a ISO mini SPDT relay (with 87 and 87a terminals, or in other words NO and NC relative to 30) ask for a fuel pump or cooling fan relay for a 1999 Jeep Cherokee.
If you need a ISO *micro* SPDT relay, ask for a fog light relay for the same vehicle.
I didn't see any dual-87-terminal relays used under there so I still don't know the magic words to ask for one of those.
hope this helps someone, it did me! (my fog lights are now legal and I didn't have to wait for anything mail-order)
Last edited:
