oil filter sandwich ground

[JJK]

In order to accommodate my oil temp sensor, I am using an oil filter sandwich that has four 1/8 NPT ports, so I will use one for oil pressure and one for oil temp. But, this adapter has electrically isolated the two senders such that they are no longer grounded. Since I am using single wire senders (Autometer), they rely on the threads to ground, which is now problematic. Does anyone know of a cheap way to ground the sandwich adapter? I was thinking of tapping a square head plug and putting a screw sideways through the square head to connect the sandwich to a proper ground through one of the unused NPT ports, but didn't know if there was a simpler, cheaper, or off the shelf alternative. I considered installing a cheap two wire temp sensor into one of the unused NPT ports so that I could tie the ground tab to the car through it thus ensuring a ground, but not sure if the ground would switch open and close via the temp sensor.
Thanks
JJ

[michael everson]

Doesn’t it ground through the center threaded part that holds it on?
Mike

[JJK]

no, the sandwich adapter is powder coated and is held in place by an adapter nipple that threads onto the block at one end and the oil filter on the other. The sandwich adapter is literally just sandwiched between the block and the filter with no bare metal exposed to anything and nothing from the block threaded into it.

[CraigS]

I like the idea of using one of your blocked ports. A couple of options. 1- buy a brass pipe thread plug to screw in to the sandwich. Before you do that, drill a hole that will allow a 10-32 machine screw to pass through inline w/ the plug. Get a machine screw long enough to pass through the brass plug w/ a brass or aluminum washer under the bolt head and under a nut on the other side. Then double nut it to lock down this screw which has enough length beyond the double nut to allow an eye type wire end to slip over it and use a lock washer and another nut to secure it. BTW even though it might require buying a pipe thread tap, I would clean the powder coat out of the pipe thread hole first. 2- Another option, and maybe easier, is drill a hole in a convenient spot in the sandwich, and tap threads into it. Something between 10-32 and 1/4". Choose a spot where you have enough material for about a 3/8" deep hole. Taps are usually tapered on their end so they start easier. But that also means a hole tapped until the tap hits bottom is also tapered. So you need enough depth for a bolt to avoid the tapered bottom. 3- A similar option is drill like in #2 but install a stud instead of a bolt. Put double nuts on the top end of the stud so you have a way to twist it tight into the threaded hole. Then you can use a nut and lockwasher to secure the wire end. Don't use a nylock because it might lock on tightly enough that if you try to unscrew it later you will pull the stud out with it.

[JJK]

I am not sure if there is a good place to tap the adapter so tapping a plug may be better. The local big box hardware stores only have brass npt plugs, any issues with galvanic corrosion using brass? I can order stainless online, should I go that route or does it even matter?

[JJK]

apparently screwing brass into aluminum is problematic, so I need an aluminum or stainless plug for this approach since the sandwich is aluminum.

[Nigel Allen]

Attach a ground wire directly to the sender?

[michael everson]

I’m with Nigel. Just solder a wire to the brass sender.
Mike

[CraigS]

Soldering heat won't affect the sender guts?

[SourceLee]

Try one of these. 1/8 NPT to 10/32 adapter. 183803

[Rdone585]

How much thread is not used when screwing in the sender? If there are a few threads, one option is to get a round wire connector that will fit the 1/8 NPT, then use a 1/8 NPT thin nut to capture it to the sender. The round connector could then be attached anywhere a ground can be found. Option 2 if there aren't enough threads is to use a 1/8" Male NPT x 1/8" Female NPT Brass Straight Adapter with the round wire connector in between.

[JJK]

Thank you all for your thoughts. While SourceLee's part (1/8 NPT to 10-32) sounds ideal, I already ordered a stainless 1/8 NPT plug to drill and tap myself per Craig S option #1, which is essentially making the 1/8 NPT to 10-32 part. As an FYI, that adapter is found in Arbor supply stores??? and costs about three times what a plug costs. Since I already have the taps, less expensive option with a little more work wins out.