What's this firewall grommet/brown wire for? Where's the tach hole?
 

Pic below shows what I'm interested in. I didn't have a flashlight with me so couldn't follow the wire all the way but it went along the LH frame rail toward the rear. Fuel sending unit? On a pickup this dimple is used for the tachometer harness grommet. On a K5, which dimple is for the tach hole and which is for an aux battery harness? If anyone has pics to post of an OEM tach harness/aux battery harness at the firewall I'd be grateful. I'm adding both in September. Thanks, Pete

Re: What's this firewall grommet/brown wire for? Where's the tach hole?
 

Not sure where the tach wire hole is supposed to be,probably one of the other dimples below this one. The tan wire is for the gas gauge.

Re: What's this firewall grommet/brown wire for? Where's the tach hole?
 

TTT ????

Any answers as to which one is fuel sender and which is Tach?

Re: What's this firewall grommet/brown wire for? Where's the tach hole?
 

The tachometer wire is red, the brown is the fuel sender DaHos

Re: What's this firewall grommet/brown wire for? Where's the tach hole?
 

Tach is Dark Brown
Fuel is Lt Brown

I do not have a blazer with factory tach to referance.........??

So my assumption would be the fuel sender wire is in the top hole as pictured but when optioned with a tach an addition 3/4 hole was drilled below the fuel sender hole. Just want to put them in the correct location as per factory.....

Re: What's this firewall grommet/brown wire for? Where's the tach hole?
 

My 1970 Blazer has been played with by other owners in the 55 yrs since it was built in Aug '69 hence the additional wires from the speedo plug, (HEI hot lead) You are correct on the Lt Brown wire, here is the location on my truck. As usual a sideways picture 😔

Re: What's this firewall grommet/brown wire for? Where's the tach hole?
 

1970 will be different than the other years due to the pink wire that is the power wire feed for the TCS system. Brown is tach, tan is fuel level.

Re: What's this firewall grommet/brown wire for? Where's the tach hole?
 

Rotated

Re: What's this firewall grommet/brown wire for? Where's the tach hole?
 

Thanks bud