# Tyco Relay as Kill Sw and PMU **URL:** \ **Category:** PMU\ **Tags:** wiring\ **Created:** [July 18, 2025, 12:52pm UTC](https://community.ecumaster.com/t/tyco-relay-as-kill-sw-and-pmu/4081 "2025-07-18T12:52:56Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Ernis\_lt](https://avatars.discourse-cdn.com/v4/letter/e/c77e96/32.png) [@Ernis\_lt](https://community.ecumaster.com/u/Ernis_lt)\ **Post date:** [July 18, 2025, 12:52pm UTC](https://community.ecumaster.com/t/tyco-relay-as-kill-sw-and-pmu/4081/1 "2025-07-18T12:52:56Z")
Searched far and wide but did not find anything regarding correct or rather safe way to wire in a Tyco/TE high current relay as a battery isolator along with PMU. Long story short, had a runaway engine, kill switch was used at around 4,5k rpm, ADU displayed “PMU overcurrent” error and PMU got fried. No fuses were tripped. As far as I can tell, power distribution is as in the image bellow, there is a 5A fuse between Relay Pin87 and PMU ignition sw input (image at bottom of the post, hand drawn). This got me questioning what is the correct way to do it with a high current relay so alternator load dump does not fry anything. I always followed the motec guide for wiring and simply setup a master switch as a condition for every output. Works and kills the engine but never tried activating the master switch under non-idle conditions. (Bellow the hand drawn diagram) But then I realized that motec does not have a wake-up/ignition sw input and ECU Master Battery Isolator shows the kill signal going to PMU ignition sw input. Any input is greatly appreciated. ![20250718_153656](https://europe1.discourse-cdn.com/flex013/uploads/ecumaster/original/2X/9/9c1b86400886ed085f10c1ad46b2024d00456c20.jpeg) ---
**Author:** ![Greg](https://avatars.discourse-cdn.com/v4/letter/g/71c47a/32.png) [@Greg](https://community.ecumaster.com/u/Greg)\ **Post date:** [July 18, 2025, 4:39pm UTC](https://community.ecumaster.com/t/tyco-relay-as-kill-sw-and-pmu/4081/2 "2025-07-18T16:39:42Z")
You need to drain current form alternator . For all relay isolateor we use spike protector with tvs diode. Have a look on wiring of manual battery isolators with 2 big and 4 small terminals when you turn it off current form alternaoer is drained to ground via big ceramic resistor. That typical installation error. ---
**Author:** ![Ernis\_lt](https://avatars.discourse-cdn.com/v4/letter/e/c77e96/32.png) [@Ernis\_lt](https://community.ecumaster.com/u/Ernis_lt)\ **Post date:** [July 19, 2025, 9:49am UTC](https://community.ecumaster.com/t/tyco-relay-as-kill-sw-and-pmu/4081/3 "2025-07-19T09:49:09Z")
I understand the need for load dump protection and ways to achieve that. I always use a TVS for installations with no PMU but it’s my understanding the PMU has an internal TVS, hence the operating voltage description: 6-22V, immunity to transients according to ISO 7637. I haven’t actually purchased the ISO but it does deal with load dump among other things. Tyco relay has load dump test data referencing the same ISO. ---
**Author:** ![DDDS](https://avatars.discourse-cdn.com/v4/letter/d/d78d45/32.png) [@DDDS](https://community.ecumaster.com/u/DDDS)\ **Post date:** [September 16, 2025, 11:27am UTC](https://community.ecumaster.com/t/tyco-relay-as-kill-sw-and-pmu/4081/4 "2025-09-16T11:27:42Z")
Could You share some sollutions according to load dump protection? All TVS diodes I search are for PCB mounting. Can’t find anything with stud mount. I also think about TYCO “change over” type relay and wired it with heat resistor to reduce load dump after disconnecting battery. ---
**Author:** ![Greg](https://avatars.discourse-cdn.com/v4/letter/g/71c47a/32.png) [@Greg](https://community.ecumaster.com/u/Greg)\ **Post date:** [September 16, 2025, 12:07pm UTC](https://community.ecumaster.com/t/tyco-relay-as-kill-sw-and-pmu/4081/5 "2025-09-16T12:07:08Z")
Here we have a ready kit > **[Hi Voltage Spike Suppressor](https://rrrshop.co.uk/products/hi-voltage-spike-suppressor)** > > Fitted to all chassis looms we produce the hi voltage spike suppressor is now available as a stand alone part made in house at RRR Engineering Used