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View Full Version : AFtermarket Tach


Ram50Man
05-02-2011, 04:48 PM
Ok so I installed my aftermarket Tach today.... it looks great, but I dont think it is very accurate. It has the switch on the back for 4,6, or 8cyl. It was way off on 4cyl sounded like my engine was gonna blow and it was only reading about 2.5k RPM, switched it to 8cyl (i have a 4cyl) it seem a little more accurate, but im prety sure my redline isnt 4k RPM, that would just be silly! I lowered the idle all the way to where my truck was just barely running and it said i was at 1k RPM still. Im wondering if maybe I hooked it up to the wrong spot on the coil.... the back of the coil only has the one post, but then right next to the coil you have a white box with 2 more posts, i hooked it up directly to the back of the coil. See pic below.

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=375&d=1304376326

Here is the Gauge though:
http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=376&d=1304381718
http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=377&d=1304381725
l.k.
05-02-2011, 06:58 PM
That thing is nice...small, not all in the way and you can def. See it well. Bright....
blindeyed
05-02-2011, 07:19 PM
I'm guessing (its hard to tell from the pic) that post on top of the coil is the positive terminal. It looks like the negative end of the coil is grounded next to that white box you mentioned. You want to hook up your Blue? (usually green) wire to the negative end of the coil, first picture.. bottom left circle.

Looks like you might have your ground wire hooked up on the right side of that white box. I would suggest moving it to a different location a bit further away. You might get an improper reading having your ground and signal wire that close together.

Tach looks good though man
4doorciv
05-02-2011, 08:03 PM
I dont remember which wire it was but I think there might be a test connector you can use as well. In my dsm harness I know where the plug is, and I don't remember where on the oem truck harness. It's been a whole where I had a carb motor in mines. That white box I believe is a resistor. Best bet is to unplug one wire each and see which wire has power to iit on key on and which doesn't.
Ram50Man
05-02-2011, 10:16 PM
I'm guessing (its hard to tell from the pic) that post on top of the coil is the positive terminal. It looks like the negative end of the coil is grounded next to that white box you mentioned. You want to hook up your Blue? (usually green) wire to the negative end of the coil, first picture.. bottom left circle.

Looks like you might have your ground wire hooked up on the right side of that white box. I would suggest moving it to a different location a bit further away. You might get an improper reading having your ground and signal wire that close together.

Tach looks good though man

The blue wire you see in the pick actually is one of the Distributor wires, but i have the Tach hooked up to the same post as that blue one. There is only the one post on the coil itself. then the 2 on the white block. But nothing is labled "+" or "-" And I dont trust the boot colors. Here is another pic with more notes maybe this one will help a bit more....

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=381&d=1304396100
blindeyed
05-02-2011, 10:27 PM
Ok, I gotcha now. My coil is a bit different from yours, so I'm giving it my best guess. Where you have it hooked up right now is on the positive terminal of the coil. You don't want to hook up your signal wire to that. The wire that appears to be "hardwired" looks to be your negative/ground wire for the coil. Follow the wire from the coil to where it mounts next to that white box you described earlier. That location is where you want to attach your signal wire. Try that out and let us know if it worked.
Acuta73
05-03-2011, 02:55 AM
Was thinking much the same, signal should be coming before the ballast, but I couldn't remember which side! (the white box is your ballast resistor, FYI)
Ram50Man
05-03-2011, 11:03 AM
Ok I will try it after work. I drove my truck here (to work) and it seems fairly accurate. My buddy was telling me that the 2.0L only has a redline of about 4k RPM's so it may actually be accurate. I hooked up my test light to see which terminal was a negative, but they all light up the test light. So I wa a little confused by that...
4doorciv
05-03-2011, 04:22 PM
Using a test light while everything is connected will show all terminals with power. disconnect the wires off the coil and test which is sending power.
DroppedMitsu
05-03-2011, 08:48 PM
The 2.0s rev limit is a lot higher then 4k, more like 6k. And they black wire is the wire that needs to be tapped as that's the neg from the coil
Ram50Man
05-04-2011, 05:34 AM
The 2.0s rev limit is a lot higher then 4k, more like 6k. And they black wire is the wire that needs to be tapped as that's the neg from the coil

uhhhh.... which black wire, every wire around the coil is black minus 1 blue one.
DroppedMitsu
05-04-2011, 11:19 AM
Sorry the black and white one hard wired to the coil
Ram50Man
05-04-2011, 03:59 PM
Sorry the black and white one hard wired to the coil

Ahh ok. you said that and I was like "ahhh there all black, now im REALLY confused!".... lol

Ok so i have tried the other 2 posts, on the white box, and the tach does nothing when hooked up to them, so im guessing the one on the back of the tach is correct, maybe my tach is just off.

HAHA im a retard.... there is a "-" symbol under the post on the coil, i just couldnt see it!
l.k.
05-06-2011, 09:34 PM
lol...did you get it all figured out.....
Ram50Man
05-07-2011, 09:23 AM
lol...did you get it all figured out.....

Yeah, i had it right from the start. I think its just the Tach itself is a little off.
dray
05-08-2011, 06:41 AM
i know on my 2.4 i use the brownish/orange female connector to hook my tach up.
Ram50Man
05-08-2011, 10:09 AM
i know on my 2.4 i use the brownish/orange female connector to hook my tach up.

I dont have anything thats Brownish/Orange, i just have bunch of blacks, and the one Blue one, but I got it now, the one post on the back of the coil that you can add wires to is the negative terminal.
abeemanator
06-05-2011, 01:28 AM
Is that one of those cheapo tachs from ebay? I had bought one, then while it was on the way I went to the salvage yard and got a 3" autogage tach for $5 so i sold the little one to a friend. The redline on my 2.0l is about 7 1/2 k rpm. I always had my tach connected where you had yours until i replaced my coil with a normal round 12v coil.
Ram50Man
06-05-2011, 09:49 AM
Yeah it is, one of those "cheapo" tachs from ebay.
camoit
06-05-2011, 12:22 PM
It could also be that the tach does not have a good ground.
slow50
07-02-2011, 10:45 AM
I always had my tach connected where you had yours until i replaced my coil with a normal round 12v coil.

ive been wanting to do this to my truck but how do you wire the round 12v coil?
abeemanator
07-03-2011, 01:35 AM
Well, I would have to check it out, I wired it up and I don't quite remember how I did it. I replaced the coil because I didn't know what the ballast resistor did, so I took it off, and after about 20-30 minutes of driving it would overheat and the truck would die. Also where you you live in Idaho?
LethalEthan
07-03-2011, 05:59 AM
the ballast resistor drops the voltage to a lower level since the oem coil doesnt need a full 12v to run. If I remember right the resistor drops it down around 5 or 6v. I had that problem on mine, the resistor went bad and the coil would overheat after about 15min and shut down. Leave the truck sit for an hour or two and it'd fire right back up. The voltage drop is also why the tach reads funny if its hooked to the resistor instead of the coil negative. I think you can run it off the resistor but only one side will give you a correct reading. As for putting in an aftermarket coil, there shouldnt be any issues just make sure everything negative on the old setup goes negative on the new setup, same with positive's
Acuta73
07-03-2011, 12:53 PM
Ballast resistors also reduce RF and EM "noise" from the coil due to the super high voltage output. Not having one can make your radio sound like poo and can interfere with other components/sensors sometimes. Even MSD/other aftermarket coils benefit from a ballast, even if just barely.
slow50
07-03-2011, 02:09 PM
so keep the ballast resistor with an aftermarket coil?
LethalEthan
07-03-2011, 03:13 PM
I'd only keep it if its needed to run the coil. I didnt have any sound problems when I switched my coils out.
camoit
07-03-2011, 04:24 PM
The ballast resistor lowers the voltage and wattage draw at an idle when the coil has more time to charge between sparks. (IE: points closed) At a higher RPM it allows the voltage to increase since the coil needs more power to charge to full power with the shorter time between sparks. When the distributor opens the circuit (IE: points open) the magnetic fiend around the coil core is allowed to collapse into the coil and the voltage is increased to a High voltage state. Normally in the (KV) Kilovolt range. That power must go some where so it runs up the coil wire looking for an easy path to ground. A Tachometer needs to connect to the negative side of the coil. As this is how it tells how many times sparks. New electronic ignition system can cause the tac not to work correctly because the grounding of the coil may not be a complete and true ground. If it has to much Resistance in the circuit the tac may be unsure if the ground is made and give you incorrect readings. Some tac manufactures require a special adapter that can read the signal the coil is receiving.
I hope this helps.