factory tach in my 94 v8, please HELP

ran94ger · #1 03-03-2010, 06:56 PM

i have the in dash tach and cluster from a junkyard ranger. im running a v8, the tach reads 1200-1300 idol. Iv not found a fix for it yet. i read on another forum about rewiring the factory tach by running a wire from the 8 cyl/ cyl post (depending on year i guess) to ground and taking out the factory signal wire and running it to the coil. i tried that and im still getting the same reading. too high. so i put it back. i know that someone has a fix for this, PLEASE HELP!
IM wondering if you need a certin gauge and or cluster or that little board that is clipped into the back of cluster. because there are 2 different tachs, they have diff. numbers on the back. one gauge has 3 screws in the face and has only 3 pins on gauge and the other has no screws in the face but has 4 pins on the gauge. so what gauge and cluster do i use??? WHAT DO I DO?????

Airtruksrus · #2 03-03-2010, 08:54 PM

Might be able to help, had the same problem when i started mine up and it depends if yours is similar in function to the one stocked in the older rangers. If you can take your tach apart from the back, there is a resistor that is mouted across two posts, this sets the rpm range for the original engine installed, as in mine changing it out to one of a lower resistance(83.3 ohms). If you can get to a local radio shack, pick up a variable resistor for 0 to 500 or 1000 ohms so that the proper rpm's are dialed in on the indicator.
Check to see if there is also a selection switch already mounted on the guage first. I'll check back and see if you have any luck in locating the resistor on the back.

ran94ger · #3 03-04-2010, 03:56 PM

Which tach do you have because I have 2. On the face of the gauge there are 3 screws and only has 3 posts in the back or do you have the gauge with no screws on face which has 4 posts on the back? Does it even matter, I don't know. Which resister, there are several, and both gauges have a dial like thing that you can turn but don't know what for. Also there is a resister going from GND 8 for the tach to theharness plug on the back of the housing.

Airtruksrus · #4 03-04-2010, 11:55 PM

I have a tach from the 86 to 88 style rangers, was thinking it might be a long shot but most are constructed internally the same when measuring the rpm. It has the three screws on the face and three on the back. There is a gas and temp guage set located at the bottom. There is a single resistor that is mounted between two posts that sets the rpm, should have taken some pics when taking apart and during the testing last time. As for pin numbers, will have to get the instrument panel out to get them off of the flex print wiring, might have to wait on that one.

ran94ger · #5 03-05-2010, 10:51 AM

I went to radio shack and they didn't have anything like a variable resister and no one knew anything. So what to do now? Do you remember what it looked like?

Airtruksrus · #6 03-06-2010, 03:11 AM

Man, sounds like you went to one of the radio shacks where there wasn't any techs on staff, only salespeople. The variable resistor I've got came from some spares that my work center throws out when they can't keep the stuff in the shop, it looks like a small rectangular block about an inch long, quarter inch tall with an adjustment screw on one end and wires along the bottom. They can come in many different configurations as long as you can get the resistance range listed on the component. Besides, I went to check on the resistor i pulled out of my tach and it was a 540K ohm(540,000 ohms, labeled with a green, yellow, white and orange stripe) resistor anyway. The only way to get you on your way is to get some pics of the tach assembly from my truck or walk you through it over by cell. This way I can do a check to make sure of the resistor that was used in mine should work in yours as well.

ran94ger · #7 03-06-2010, 06:36 PM

I don't have any resister that looks like that. I think I might of seen those resisters at Radio Shack. I guess I would have to adjust it with an ohm meeter right? OK now where to put it? There are 2 adjustable things on the tach which i turned them both down counter clock wise. The idol dropped to about 1000 rpm but thats all. I have 2 pictures on my home page if you want to see what im talking about. LOL, I didnt know how to get them on the thread. Sinse what i did helped I wonder if i get one of those things (which i saw at radio shack also) that has higher or lower ohm reading. you think it would be higher or lower? this thing has 3 posts on it, but i dont know how to tell what it has now. My cell # is 301-452-5648 if you think it would be easier to talk about it and im in MD.

Airtruksrus · #8 03-07-2010, 09:58 AM

Talk about a complete upgrade from what i've got. I'm not too sure what the adjustments are for unless i can find the schematics to give a clue. Almost willing to bet that they are for doing the adjustments, one for a rough adjust and the other for the fine adjustment. When you use the meter, check the two posts on the ends of the resistor to find which one has the higher ohm reading, should set the rough adjustment. Won't need the meter when doing the adjustment, go by the reading on the tach and start with the original adjustment when it was at idle, then adjust it to one half and should give the reading for the v8. I was using an electronics tester to find the value of the resistor needed for mine. Yours is much simpler and doesn't require scrounging for the right resistor. Hope it helps.
The tach that i pulled out of a mustang had an adjustment labeled 4 - 6 - 8 right on the face plate and couldn't make it any simpler but had to find out the hard way on mine.