E Body 4 speed Reverse Light

I'm looking for a little info. What size of hole do I need to drill for this in the firewall? I know where the hole goes, just want to know how big to make it.

Thanks

Tav

If you have the four speed reverse harness it should have a rubber gromet that fits in the hole you want to drill.
Mic the gromet size and drill hole slightly undersize. This way you will have a good snug fit.

Reason: I have found that sometimes the gromets on repo harnesses are not the same as original and do not fit in there snug so it does not keep falling out.

Depends on what year you are working on. 1970 only used the small grommet and most 71 and up used the larger style grommet.

That's very interesting, thank you! I'm working on an early build 70 challenger. Anyone have the dimension for that?

So then, the cruise control harness which used the same hole probably also used a small grommet in 70 and the larger grommet later on?

dimensions of either hole size would be helpfull though. I'm helping M&H collect the info needed to make reproduction harnesses.

Tav

A measurement on the recess of two grommets allowing for a snug fit, shows 1" on the large one and 3/4" on the small.
That should be the size to drill, but a true measurement on a 70 and 71 firewall with the grommet removed would be more accurate.

My 70 cruise harness grommet also measures 3/4.

From my experiences with power window grommets, I think the sheetmetal hole will be 1/8 smaller to provide a super snug fit for the grommet.

I was hoping someone could chime in with some actual firewall measurements to verify this. Surely someone out there must have a 4 speed E body in mid-restoration with the grommet out so they can get an acurate measurement?

Tav

the hole in the fire wall is 1in the grommet is 1 1/2 for 71 b-body and the fire wall is same as a ebody

Anyone have a 1970 firewall to measure?

Tav

cataclysm80, you have an e-mail. I will try to measure my AAR in a little bit and get back to you.

Thanks for the pic, measurements would be great!

Here is the pic to assist others in locating the hole that needs measured.

Tav

The hole in mine measures 3/4 in. I didn't have a caliper handy but with a 6 in ruler from the backside lined up on the inch mark the 3/4 mark was at the edge but not fully visible. Hope it helps!

Thank You.

Tav