What is this?

I am rebuilding my 78 GMC K15 and have removed all the wiring from my cab. I took pictures of where everything was routed, but I have since smashed my phone and lost all my pictures. There is one piece of wiring that I took off the firewall under the hood that is broken. I'm not sure what it is, so any help you guys could give would be appreciated. I need to know what it is so I can replace it. Also if anyone has pictures of how all the wiring is routed, that would be great as well. Thanks

Looks like a condenser, maybe for the radio? Someone smarter than me will let you know soon.
If I haven’t before
Welcome to GMSB from Virginia

The only piece like that I remember being on the firewall, is for the fan motor. Iirc, it's a noise suppressor for the electrical feedback. The m1008 trucks had them on the horns and blower motors too. They usually caused too much draw and overheated the circuit. You can leave it off if that's what it turns out to be. The only thing that doesn't seem right to me is the plugs are different at each end. The pieces I'm speaking of had the same plug on each end so they could be bypassed by simply taking it off, and plugging the harness back into the component.

Diesel trucks had them on the tach as well (inside the cab) or it might have been the clock.

Looks like a tach filter. If so, the single connector will plug into the TACH terminal on the distributor cap and the tach signal wire will plug into the bigger connector (one half of that one goes unused).

Thanks for the replies. So it sounds like if I can't find a replacement it won't be a big deal? It can be left off? I had a friend who thought it was a filter for the radio as well. All I know is it came off The firewall, just to the left side (drivers) of the motor

Cemack said:

Thanks for the replies. So it sounds like if I can't find a replacement it won't be a big deal? It can be left off? I had a friend who thought it was a filter for the radio as well. All I know is it came off The firewall, just to the left side (drivers) of the motor

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That location would be a tach filter. Does your truck have a factory tach?

bucket said:

That location would be a tach filter. Does your truck have a factory tach?

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Yes, factory tach. Do I need it then?

That looks exactly like a ferrite bead to me, you can pick one up at your local electronics store for $1 or just take one of your old computer power supply. I dont know much about cars, but I am a electronics engineer. ferrite beads are used to filter out noise from electrical lines. You can buy them in almost any size to fit the wire you want. You can even put 1,2,or 3 of them on the same wire. Some are clip-ons, some look like diodes , some are non removable. Just use a clip on one and your good to go! No more engine nose on your line. This probably keeps the bzzzzzzzzz out of your radio stations or any other electronic device that might be affected by noise. Ferrite beads filter electric noise from your ground that your electronic device might pick up, like from a electric fan motor. Cars dont really have grounds, so noise can affect a lot of things and make things operate strangely.

That is your tach filter and yes you need to use it.

Thanks everyone. After checking out checking out tach filters on the old Google machine, that is exactly what it is. I will try and find one at the local pick "n" pull. If not, I see you can buy them on line through a few different sites.
Would never have figured out what it was without your help. Thanks again

Glad ya found it! Says tach will work without it but the needle might be a bit jumpy like a mexican jumping bean. Here is a schematic if ya want to build one yourself for less than a dollar. It came from GM. Its just a couple of resistors in series and couple caps to pull it down.

BBBURB said:

Glad ya found it! Says tach will work without it but the needle might be a bit jumpy like a mexican jumping bean. Here is a schematic if ya want to build one yourself for less than a dollar. It came from GM. Its just a couple of resistors in series and couple caps to pull it down.

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****! Who knew?