|
|
|
Your donations help keep this valuable resource free and growing. Thank you.
|
70 Javelin instrument circuit board ground |
Post Reply 
|
| Author | |
White70JavelinSST 
Supporter of TheAMCForum 
Joined: Aug/08/2012 Location: Minnesota Status: Offline Points: 4866 |
 Post Options
 Thanks(0)
 Quote Reply
 Topic: 70 Javelin instrument circuit board groundPosted: Jul/19/2018 at 1:30pm |
|
I'm having trouble remembering how the instrument cluster circuit board is grounded on the 70 Javelin. I do remember the circuit board has male pins on it that a wire plug fits to, but I cannot recall if that plug has a terminal used just for grounding or if the circuit board itself is grounded by being bolted into place somehow, like a jumper wire to ground. I'm thinking the former is the way it works because everything in that area there is plastic, and I cannot remember attaching a ground behind the dash. Also would the engine block to chassis ground affect the ALT light? This is related to the ALT coming on, the fuel gauge dropping to zero, but both of these act somewhat intermittent. Like they both work correctly at startup and for a period of time, but then the ALT light comes on and the fuel gauge drops to zero. The voltage at the battery reads over 14 when the engine is running. over 12 when key is off. |
|
|
70 Javelin SST, second owner, purchased 1972
|
|
 |
|
|
THE MENACE
AMC Addicted 
Joined: Nov/04/2008 Location: So. California Status: Offline Points: 4438 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/19/2018 at 3:33pm |
|
It's been a while, nut IIRC my 70 AMX and 70 Javelin have a grounding strap that is attached to the post of the headlight switch and runs over the one of the cluster mounting screws.
|
|
|
Former Owner of:
The Craig Breedlove "AERO AMX" Still Owner: SS/AMX #9 replica (THE BIG MENACE) 70 AMX 416, EFI, Nash 5 speed 70 Javelin 401, 727 (Wife's car) 72 Gremlin Autocross Project. |
|
|
|
|
amxdreamer
AMC Addicted
Joined: Jul/30/2008 Location: Vancouver, BC Status: Offline Points: 8509 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/19/2018 at 6:10pm |
|
That is correct Dennis
|
|
|
Tony
Vancouver, BC 1970 AMX 1972 Badassador AMO#10333 |
|
|
|
|
White70JavelinSST
Supporter of TheAMCForum
Joined: Aug/08/2012 Location: Minnesota Status: Offline Points: 4866 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/20/2018 at 8:31am |
|
Thanks
|
|
|
70 Javelin SST, second owner, purchased 1972
|
|
|
|
|
White70JavelinSST
Supporter of TheAMCForum
Joined: Aug/08/2012 Location: Minnesota Status: Offline Points: 4866 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/23/2018 at 12:23pm |
|
Please billd can you respond to these questions.
Would the engine block to chassis ground affect the ALT light on the gauge cluster instruments? A voltmeter placed across the battery with the engine running reads over 14 volts even when the ALT light is on, so I assume the alternator is actually charging. The battery retains well over 12 volts when the engine is not running and hasn't run for several days. Optima Red Top battery. This is related to the ALT light coming on, in conjunction with the fuel gauge dropping to zero, but both of these act somewhat intermittent. Like they both work correctly at startup and for a period of time, but then the ALT light comes on and the fuel gauge drops to zero. If the car is shut off for a period of time everything reverts to normal for a while. Bill, I'm really confused on this one, the fuel gauge suddenly drops to Empty, when I know there's fuel in the tank and the ALT light will come on. I've crawled under the back end of the car and wiggled the fuel sending "positive" wire and things go back to normal for a while? I've removed, cleaned and made sure the ground at the tank is good, both ends of it. Any thoughts Bill?
|
|
|
70 Javelin SST, second owner, purchased 1972
|
|
|
|
|
george w
Supporter of TheAMCForum
Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/23/2018 at 7:29pm |
|
The instrument cluster ground is provided through the black wire in the round connector plug. The black wire goes through a splice or two and grounds to the body further down the line, I believe in the engine compartment passenger side inner fender or firewall area. The short copper strap is used for the optional clock. It's goes under the upper left screw of the cluster housing to the underside of the clock upper mounting tab. The strap provides the ground for the clock through the cluster housing. The housing ground is through the screws that attack the pcb to the metal shell. With electric wipers there's a another, longer copper jumper strap that grounds the wiper switch body to the headlight switch body. The headlight switch has a separate grounding tab on the very back of the housing that connects to the black body ground wire group. At least on 68 and 69 models this wiper to headlight switch strap is on the back side of the dash.
|
|
|
Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.
|
|
|
|
|
billd
Moderator Group 
Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/24/2018 at 2:50pm |
That is to ground the wiper switch. There is indeed a strap that goes from the wiper switch to the cluster ground. The headlight switch has a tab for a black ground wire as well - that is how it is grounded. However, the cluster is grounded via a BLACK wire in the round connector. That black wire in the round connector goes to the same black chassis ground that the headlight switch black wire goes to. The reason the wiper switch uses that brass strip is because the wipers were optional and the ground necessary for wiper operation was not included in the main cluster or cabin wiring. So the fix was to ground the optional electric wipers to the cluster ground using that strap. (EDIT - oops, George is correct, that strap DOES go to the headlight switch so the wiper switch can share the headlight switch ground - geesh, think about those brass straps you have in the parts bin, William, and the TWO large holes and the shape. Goes over both to ground the wiper switch through the headlight switch ground. ) Bottom line - cluster gets ground via black wire in round connector that goes to a common point where about six other ground wires come in, and then is grounded to the chassis - firewall area I believe, but that isn't critical - the fact the black wire in the round connector is what grounds it is important.
Think about it - no electric wipers - no electric wiper switch, so it can't ground the cluster. anyway..... I'll read the other stuff to see what's going on....... Edited by billd - Jul/24/2018 at 2:53pm |
|
|
|
|
billd
Moderator Group
Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/24/2018 at 3:10pm |
|
The alt light gets power from the ignition switch - power through ign switch to the cluster pin, through the trace on back of cluster, to the bulb socket, through bulb, through another trace, out another cluster pin to orange wire exiting cabin.
From there is goes to the back of the alternator AND the regulator. The ALT light does two things - one is to supply power to the regulator which is then fed to the alternator through the green wire to the brushes. That "Excites" the field and gets things charging. Once it starts charging, there is output at the REG terminal on the alternator which goes out the orange wire at the alternator and is now used to power the field. Remember that also came from the ALT light inside........ normally the outer side of the bulb grounds through the regulator and then through the field to ground. Once the alternator charges, there is now + at that end of the orange wire. +12 from the ignition switch to the bulb on one side and now with things charging +12 volts on the other side means "lights out". It's no longer grounding out there, it's being supplied + potential. I said 12 volts but really should say "system voltage", whatever that is during operating, typically around 14 volts. OK 14 is about right for charging. Battery - with surface charge removed 12.6 is normal. It may be more with surface charge (to remove surface charge, turn on headlights for 30 seconds, then turn them off, then wait a few seconds and measure battery voltage - it should settle around or about 12.6 volts) Anyway, engine running, alternator charging, you have power coming back in to the ALT bulb. I'm mentioning this because the ALT light being on can be due to power from EITHER direction..... finding ground either out in the alternator or inside somehow. OOps, gotta run, D-I-L here with grandson......... more later, sorry!
|
|
|
|
|
billd
Moderator Group
Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/24/2018 at 9:47pm |
|
OK, I'm back for a while........
Anyway, with the alternator charging, there is power applied to both sides of the bulb - The 4 amp fuse handles not only the ALT light but also gauges. So what can happen if there is a poor connection at the gauge fuse, the ALT light may come on because it's grounding through other items - and at the same time those other things fail to work. I'd check the instrument cluster black ground, but I more suspect a problem at the fuse panel - especially around that small gauge fuse since it handles both ALT light and gauges.
Weird things can happen with ignition switch troubles, too........ |
|
|
|
|
Post Reply
|
|
Tweet
|
| Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |
Click for TheAMCForum Rules
Topic Options
THE MENACE wrote: