i need some answers asap PLEASE

[GREASEMONKEY72]

where should i run the wires for the tach to on the fuse panel? (autometer tach) it was working right but now its not so i need to know where it should go



my speedo wont go over 85 and is also about 5mph off at lower speeds according to my brothers 05 f250, but i pulled it all out tonight and it looks like the cable turns a magnet and it turns something else which in turn makes the needle move, but i couldnt get the needle to come off to pull it apart further and i would like to know if i should even worry about the speedo or if i should be looking at the trans where the cable goes in


and also would the tires affect the speed reading?, according to the side wall they are 31s even though they are actually like 29in tall i think

any and all help and insight is greatly appreciated

[cableguy0]

tires will definately affect the speed reading on the speedo. a couple inches too tall will make you 5 mph off.need more info on the tach. should be 4 wires one ground one to the distributor and one for the light in the tach to turn on with dash light and one for power to the tach. distributor should be green/power red/lights white/ground black. the power wire needs to go to a keyed ignition source meaning that the terminal only has power when the key is turned on. check your ground before you do anything else. also make sure that the green wire is still connected to the distributor

[GREASEMONKEY72]

im a retard in more ways than one..haha...i shouldve known about the tires(brain fart) but anyway yea the 4 wires you named are correct ofcourse and the rpm reads fine but the other night the light wasnt coming on and when i stepped on the brake the needle went crazy then my brother put it into the ac fuse (i dont have ac) for a temp fix and it worked fine but tonight it doesnt, but then i havnt checked the ground, i didnt put the tach in the PO did and now im confused, but i do intend on getting a secondary fuse panel just for the tach

[cableguy0]

no need for a secondary fuse panel.there are enough places to simply add a tach there a few spade terminals on the fuse block you just need to find one that doesnt have power with the key but has power with the key on.im going to bet you have a bad ground. grounds are the most overlooked thing in every electrical system in a vehicle.your only issue the actual tach light? for all it matter you can run the tach light to wherever your tach is getting power and have it lit all the time. it wont hurt anything i ran mine that way for years.

[GREASEMONKEY72]

i forgot about checking the ground and i dont know why its usually the first thing i check, but ill check it and see what happens


any info on the rest of my issue with the speedometer???

[Chevy_Man]

I found that a gps works pretty good when wanting to check your speed, just check the gps in something that you know the speed is right and then jump in the old truck...

Eric

[GREASEMONKEY72]

i dont have a gps

[GREASEMONKEY72]

well i fixed my tach and it was the ground, thanks for the help guys, but im still wondering about the speedometer

[cableguy0]

its possible your cable is binding up. is the speedo bouncy at lower speeds? or does it just stop at 85 and thats the only issue?