MSEL Battery Isolator Question

Hello all,

Been a while since I have posted here. Lets get into it. I am building a harness for my 2013 WRX. I am using a Haltech Nexus R5. I am not doing a full rewire of the car, only using the Nexus for primary engine functions, fuel pumps, fans, etc. Overkill, I know, but I had the R5 left over from a previous build I decided to go a different direction with.

Onto my question. I want to wire in a MSEL battery isolator, just to add more protection. The instructions say to go from the Battery to MSEL and from MSEL to PDM/Fusebox, Alternator, Starter. However, the stock wiring in the WRX goes from battery to starter/fusebox and the alternator on it's own wire, with a 120 Amp fuse between the battery/starter and alternator. If I am using the MSEL, am I tying all of those points together?

I hope that makes sense..

Cheers,

Kevin

Kevin,

Placing the MSEL unit between the battery and that split provides a single point of interruption of the whole system.

I appreciate the response! I guess I should add that I am relocating the battery to the trunk and if I were to wire it that way, I would add a great deal of additional wiring if I were to do it that way. I will add a drawing of what I have going on in my mind.

The first image is stock, the second image is relocating the battery to the trunk, with the MSEL.

Basically in my head I would go from battery to MSEL, MSEL up to the firewall, firewall to PDM, Starter, Fusebox, and Alternator. I would remove the 120 Amp Fuse and tie the original battery wire and alternator wire to a single post.

Kevin,

Sorry, if you've attempted to upload images I'm not seeing them.

Let's try this again.

Bump

What you have drawn as MSEL is the equivalent of the MSEL suggested wiring posted above.

Awesome, thank you! So it's OK to wire it that way, removing the 120 Amp fuse in the stock fuse box? That was the main thing I was worried about.

Usually when the MSEL unit or similar and a PDM are present and governing all electronics on the vehicle, fuses are not used. The battery isolator and PDM both have short protection which is what the fuse was there for on the stock system.

I understand that. I'm only using a few of the high current outputs of the Nexus. Namely, to power the coilpacks, injectors, fans, fuel pumps, and DCCD controller. The rest of the car is running the stock wiring. I'm not ready to rip out all the stock wiring yet, so I'm just using what makes sense for my application as it sits.

In that case, anything not PDM controlled, should be fused.

That's pretty much what I was asking about. Stock fusebox itself will be in its original location. I'm just trying to figure out how to run the power cable for the MSEL Isolator. If I were to remove a fuse, it would only be the main large 120A fuse, in order to run the power as MSEL recommends. Since the alternator, from the factory, connects to one side of the fusebox and the battery power is on the other side. Separated by a 120A fuse.

I assumed you would put the fuse in the alternator line (alternator to firewall). That is what needs to be protected.