one relay for 1 wire doorlocks

Would this work? 85.lock(-) wire from remote start unit 86.12v fused constant 87a.unlock(-)wire with resistor from r/s unit 87.to ground with resistor for lock 30.to cars doorlock wire.

what car is it is it type f locking or just two negs to the one wireWhy oh Why didn't i take the blue pill

Darren Power

Would probably be erratic.........Depending on the GROUND from UNLOCK.  Remember it still has to activate Relay for LOCK also. Usually the reason to use Relays is the Problem of the Unit not having strong enough GROUND or Negative Output for Resistors or Grounding Type DoorlocksMO

Don't Learn from Others Mistakes

You Might Be the One That Knows.

No way. The relay setup you describe would have the lock wire resting with the unlock resistor in place. Just not gonna work...Mike M2

Tech Manager

CS Dealer Services

Draw it out on paper,The lock wire from r/s unit goes to term 85. The unlock wire from r/s unit w/resistor is at 87a. When you hit unlock on remote the neg pulse will go thru 87a out thru 30 to car wire. When you hit lock on the remote term 30 connects with term 87 which is grounded w/resistor. I don't see a problem except for like MO12v said,that the ground from the r/s unit might not be good enough for this.I have tried this and it does work.

Sounds pretty clever to me. It can't rest at lock because 87 is only connected to 30 when a lock pulse activates the relay through 85. It can't rest at unlock because the normally closed relay circuit through 87a and 30 doesn't complete the path from the vehicle's wire to ground (through the resistor) until a ground pulse is provided to 87a from the R/S Only unknown is how much resistance the R/S unit has through it's unlock wire and whether or not it would effect the desired resistance value of the unlock circuit.

Of course, if the lock and unlock circuits from the R/S are good enough why use a relay at all? Why not just throw the resistors in line with the - lock/unlock wires, tap them both into the vehicle's doorlock control wire and call it a day?

because it's not a true ground and you'll have erratic operation....Kevin Gerry

Certified Electronics Technician

MECP First Class Installer

Owner/Installer

Classic Car Audio

since 1979

natsys wrote: Of course, if the lock and unlock circuits from the R/S are good enough why use a relay at all? Why not just throw the resistors in line with the - lock/unlock wires, tap them both into the vehicle's doorlock control wire and call it a day?

I've seen it done that way with no problems; however, many alarms send a positive pulse on one wire at the same time as a negative pulse on the other.

Yes, dual polarity doorlock outputs would only add to the problem, and they were on my mind when I asked the question. It was, however, posed more to point out the line of reasoning of the original scheme which ultimately locks through a relay, but relies on the ground pulse of the R/S for unlock. Either you should have relays on both lock and unlock, or you shouldn't and can use the neg. doorlock outputs from the R/S with resistors. For the cost of 2 relays, I'd personally go with the relay setup. Reliability is key to a successful install, and although the setup described would theoretically work, it is basically using half setup with relays and half without relays. I've often wondered what kind of load that whiff of a ground pulse out of an alarm or R/S would handle. The experience on this topic seems to indicate that it is best not to trust them with too much.