Runing wire from cabin thru cowl into engine bay

[rossman]

I'm planning out my ECU install. The current plan is to run the power and signal wire (~3/4" bundle) thru the cowl and out the hole where the windshield wiper wires passes thru. I am doing this because I want to mount my ECU in the glove box and the space below it is filled by the AC blower/evaporator box. The box is up against the firewall so running wire behind it isn't a good option. The most direct way appears to be thru the cowl. Has anybody done something like this before? I'm a little worried that the high pressure in the cowl will force air/water thru the hole. I plan to install an 3/4" EPDM grommet and wrap tape around the wire bundle to get a tight fit. Will this type of routing be problematic from a air/water sealing perspective?

[rossman]

I'm just going to go with it. Going to use some large shrink tube to cover the cable in the exposed areas. I'll just dab on some silicon if it leaks around the grommet.

[RebekahsZ]

Make sure you plan for the size of any wire-end connectors (and not only the wire bundle diameter) when you plan for the size hole to drill. I have an LS2 ECU and wiring harness - the connectors are HUGE. I'm gonna leave my ECU on the firewall just to keep it simple.

[rossman]

Its funny you mention that. I purchased a weather pack kit from DIY auto tune. I didn't realize how big those connectors are until I opened the box! I'm seriously thinking of going with something more compact.