battery cut off switch

[dsobering47]

I also have a M52B28 swapped e30.

I guess my confusion is mounted from the research I found from others not needing the additional grounding. I understand the necessity for it, so I would rather "over-build" something correctly than just "have it work".

I will be running a two-pole ignition switch (only KL30) and a push button start switch. My kill switch is the longacre 4-pole model...which I assumed would suffice if I retained the in-line fusible link for the DME/relays on the smaller post. Since its a 4-pole switch, I do not have the additional upper two terminals (Isnt that a 6-pole switch then?).

Any input is appreciated for this clarification

[Jparkr]

I think the easiest answer to this entire thread would be to just buy this one:



http://www.longacreracing.com/catalo...=1568&catid=14

[dsobering47]

LOL, thats the kill switch I purchased. I thought that switch already used a built-in system for dissipating excessive voltage/spike from the "kill" movement....

[!kid]

LOL, thats the kill switch I purchased. I thought that switch already used a built-in system for dissipating excessive voltage/spike from the "kill" movement....

the switch it self would have to be grounded for it to have a built in system right? that switch has such a high amp ratting! I kinda wish I bought that one. Having a hard time finding a 60-80 amp relay in my area.

[jlevie]

I get the relay I use from http://www.wiringproducts.com

[!kid]

I found a relay that should work its 70amp part# NTE-R51-1070-12F. got it for 10$ at a store in Costa Mesa, MarVac Electronics.

[dandrewg]

jlevie, do you use the 60A automotive relay or the 80A surface mount relay from that website?

[jlevie]

I use the surface mount relay. The best place to mount the kill switch and relay is within the area protected by the cage (and route the power cables inside of the cage). I add a plate for the kill switch and fire bottle pull at the junction of the main hoop and harness bar. That location is easily accessible by corner workers, but still protected. And it is easy to add a mount for the relay to either of those bars.

A also advocate relocating the battery to place it against the right down tube in the trunk to get it out of the rear crush zone.

My first car (destroyed at Road Atlanta) had the kill switch in the position described above, but the battery in the OE location. The damage to the right rear quarter came within a hair's breath of causing a major short in the power cable and since the integrity of the gas filler neck was compromised if a short had occurred there could have been a fire. The damage to car meant that a kill switch mounted in the cowl or rear deck would have rendered the switch inaccessible.

[NigelStu]

Trouble-shooting post here:

My car is setup with a HD master cut-off but currently NOT wired with a relay (my bad for not checking the draw of the DME...) Have run approximately 60 hours with current setup. Switch is this one:

switch

Main cable through main posts, DME cable through the pins, alternator protection / resistor on other pins.

Last race we ran, 2 of the drivers experienced some power cut-out after running over some curbs - 1st driver RPMs drop momentarily then back on once. 2nd driver, the first few times the same as driver 1. Later, the engine completely shutoff after rumble strips.

Is this type of symptom possibly a kill-switch going bad / over-cooked connection?



We tried diagnosing while in the pits, but could not duplicate by shaking/hitting different electrical components (DME, AFM, dash where kill-switch is mounted, main/fuel relay) and did not have issues again.

My first thought was that it could be a bad CPS, or CPS that is shorting out only when vibrating over rumble strips. Upon removing CPS, I could not see anything physically wrong - no crimped or worn/exposed wires (new with ~24 hours on it at this point).

Could the culprit be the master kill-switch? Or do I need to be looking elsewhere?


TIA

[jlevie]

Once diagnostic would be to measure the resistance across the DME contacts. Another would be to tie a test light from the engine side of the DME contacts to ground and see what happens on track.

[NigelStu]

While I will do on-track data checks (voltage check at that point is a great idea) if I cannot definitively find the issue before we hit the track again, I'm really looking to fix it before we get to competition again. I don't want to throw away a good finish with an unknown. This gremlin popped up in the last event, but I"m not sure where to look.

So... Is a failing kill-switch a possible reason for cutting out like it did after running over rumble strips? Or should I be looking at DME, AFM, throttle, CPS, etc?
Keep in mind that it was very intermittent and only when running over rumble strips. Also, after the last instance where the car died and wouldn't restart, once towed back in the pits the car fired right up and didn't hiccup again over then next ~3.5 hours....

[jlevie]

The car cutting out when on gators is a sign of a loose connection or something grounding out. Reasonable possibilities are the CPS wire on an M20B25 if it isn't routed through the plastic chase, the kill switch, a bad fusible link in the DME cable, a loose DME ground, loose coil connections, bad main or fuel relay sockets, etc.

[NigelStu]

perfect - thanks. hadn't thought about fusible link. I will add that to items to check.


So far, CPS ruled out since physical inspection indicates no issues with inadvertent grounding. Relay bank, coil and kill switch have the largest probability to me (due to relay/coil being original to car and kill switch based on this thread), so I'll put those on the list to check first. I just wish I had access to a 4-post shaker to check this stuff out before I hit the track! Just need to figure out a way to isolate each item to figure out the culprit.

[cjm]

Have a somewhat related question.
For storage purposes only - so that the battery does not go dead when the car is not driven for weeks at a time.

Is there any problems with using a switch to just disconnect the negative terminal of the battery from grounding to the body?

[seatown88]

I think the easiest answer to this entire thread would be to just buy this one:



http://www.longacreracing.com/catalo...=1568&catid=14

Perfect, one 175 amp main circuit and one 125 amp alternator circuit! Should be more than enough to handle any spikes.