I got a junkyard stock tach for my truck ('85 F150 5.0L V8), it didn't come with one stock. There was a blank space in the cluster just asking to be filled.

Since my truck didn't come with a tach, the printed circut film on the back of the cluster doesn't have tach connections.

The back of the tach has 4 posts marked "C", "G", "B" and "8". I have wiring for a Sun tach that died about 2 years ago. It has red, white, black and green wires. Red is 12v, green to coil, black to ground and white to the dash lights.

I connected the green to the "C" post, the black to the "G" post, the red to the "B" post, and nothing to the "8" post. The tach seems to work, but I think it may be reading high. I have no way to confirm the reading as the old tach is dead.

I can supply the part # off the front of the tach if that is any help.

85 F150 4x4, Bal & BP 302, EFI, K&N air filter, Heddman headers, High-flow Cats, Custom side-exit exhaust, 4" Rancho lift, Rancho 9000 shocks, Rancho Torque Arms, 4.10:1 gears, Rear limited slip diff., 33" BFGs, Warn Winch, SnugTop.

 

What size engine was the donor tach attached to? I know that my aftermarket tach had a switch to go between 4-6-8 for the cylinders.
I never experimented to find out if the tach read any different on the wrong selection but if I am right I think it would read higher.

 

>What size engine was the donor tach attached to?

I don't know. The cluster was pulled and stored inside the junkyard shop. The dead Sun tach had the switch too. It seem logical that if the tach was from a 6, it would read about 30% high.

I'll call the yard to see if they know what it came out of.

85 F150 4x4, Bal & BP 302, EFI, K&N air filter, Heddman headers, High-flow Cats, Custom side-exit exhaust, 4" Rancho lift, Rancho 9000 shocks, Rancho Torque Arms, 4.10:1 gears, Rear limited slip diff., 33" BFGs, Warn Winch, SnugTop.

 

Look at the PN molded into the back of the tach - for 6s, the last digit should be Y. The one from the front is the PN for the face. Mine is EOTF-17360-Y.

 

I'll have to dig it up again, but, the 8 terminal has to be hooked up for a V8 application, I just can't remember what to...
I normally just grab the entire cluster, but, I had to fool with it a bit to get it to work properly with my 300 I-6 when I first installed it(it was out of a 302 truck) and again when I put the cab on my F250.
Evan
86 F250 HD XLT Lariat Explorer 4x4 ex. Extended Cab: 460 with factory 2.25" catless duals to the muffler(still running the stocker aaargh)
/T19(syncroed granny low)/BW 1345/3.55 geared Full Floater 10.25 and Dana 50 TTB/ 265/75R16 Hankook FR04's on 16x8 Whitespokes(street tires... Need mudders)
78 F150, 351M/C6, eventually to be repowered with a 400

 

>Look at the PN molded into the back of the tach - for 6s,
>the last digit should be Y. The one from the front is the
>PN for the face. Mine is EOTF-17360-Y.

I was thinking that there shoudl be different tachs for 6s and 8s, but, the parts guys at 2 dealers said that there was only one tach made for the '80 - '86 range. No diffentiation between 6 and 8 cylinder applications!

When I asked one guy how the tach would know if it was attached to a 6 or an 8 he said "I don't know. The engineers didn't let me in on that one when they designed it". Ha Ha Ha.

85 F150 4x4, Bal & BP 302, EFI, K&N air filter, Heddman headers, High-flow Cats, Custom side-exit exhaust, 4" Rancho lift, Rancho 9000 shocks, Rancho Torque Arms, 4.10:1 gears, Rear limited slip diff., 33" BFGs, Warn Winch, SnugTop.

 

>I'll have to dig it up again, but, the 8 terminal has to be
>hooked up for a V8 application, I just can't remember what
>to...

I tried attaching the coil wire to the "8" terminal and the tach didn't read at all. I also tried it with the 12v attached to the "8" with the same results.

I have to go back to the yard soon. If I can get this figured out before then I'll see if they'll sell the printed circut film off the back of the cluster that tach came out of, of maybe just the bare cluster as it only had a gas guage and speedo remaining after I got the tach.

If you can dig up where, or to what the "8" terminal is attached, that would be a great help!

85 F150 4x4, Bal & BP 302, EFI, K&N air filter, Heddman headers, High-flow Cats, Custom side-exit exhaust, 4" Rancho lift, Rancho 9000 shocks, Rancho Torque Arms, 4.10:1 gears, Rear limited slip diff., 33" BFGs, Warn Winch, SnugTop.

 

Look in the Haynes manual - it shows the wiring fairly well.

 

I posted a wiring color connection in the electrical forum

Dennis

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Thanks to all who tried to help.

Got the printed circut off the tach-donor cluster.

 

Brian,

I had a similar question back in April when I was trying to hook up a factory tach in my truck. The thing is, I had the entire cluster unit with the tach, but my wiring harness didn't have the tach wires so I couldn't figure out what the tach was supposed to hook up to.

Here's the thread:

https://www.ford-trucks.com/dcforum/DCForumID92/6981.html

The following may or may not pertain to you, since your truck is an '85 and the wiring harness is probably different.

Once I figured out the tach wiring (thanks to Dennis), I ran into a strange wiring quirk when I was hooking it up. On the '80/'81 trucks, there is a significant instrument cluster wiring difference between tach-equipped trucks and others.

The way the '81 printed circuit was set up, the +12V power lead for the tach is shared with the right turn signal indicator, which has a separate, switched ground to flash the bulb. The left turn signal indicator uses the common cluster ground and a switched positive lead to flash. Is this weird, or what?

I wound up clipping the printed circuit to break the connection between the signal indicator +12V lead and the tach, and I ran a separate +12V wire to the terminal lug on the back of the tach.

Works great now.

 

[updated:LAST EDITED ON 25-Nov-02 AT 09:19 PM (EST)]With the 85 trucks, it's a plug and play application. My truck stock had no tach. I ran to the junkyard, picked me up one, plugged it in and whala it works. The tach was from a v-8 equipped truck and according to the timing light and a sunpro tach that I temperarily hooked up, the tach is dead on. BTW, my truck is an I-6.