I have a 70 Chevelle. The engine harness is from a 70 malibu, the dash is a SS idiot light type from a 72 monte carlo with the 72 monte dash harness as well. I bought a kit to change the idiot lights to the tach and gauges. Nothing works right at all. Whats the problem? Are my harnesses not compatible? I have a new voltage regulator, horn relay, and all the sending units are new. The circuit board is new and so are the gauges from the kit. Whats up? Help would be greatly appreciated. Thanks

I have read that the '71 and '72 are not the same. The wire positions in the fuse block are said to have changed in '72.

One big difference is where the dash harness gets the 12 volts from the battery. That's why nothing works.
Chevy made a change in 72. In 72 the fuseblock and dash harness gets power from the engine harness. This comes from the horn relay mounted on the firewall near the brake booster.
In the prior years 12 volts comes in through the lamp harness from the horn relay. Horn relay was mounted up in the front by the radiator.

Hey, thanks for the help. I was wondering if i could just rewire the fuse block so that the correct wires are in the correct positions. This would be alot cheaper and easier than going through the hassel of taking it out again and finding a 70 or 71 dash harness.


graemlins/beers.gif Thanks

Yes you can rewire the bulkhead connector. I think I have a procedure. I'll check when I get home.

Thanks Elree. I have an original 70' assmbly manual with all the wiring diagrams that is very useful if you can understand what you are looking at. I would still like to get my hands on a procedure though, just to check my work. I decided that removing the harness will make it easier, so i have done that and i am about halfway done with rewiring the fuse block. No wonder the darn thing didn't work! Thanks for all your help everyone.


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The following directions should provide the necessary information to modify your 72 harness for use on your 70.
If you look closely at the wire side of the dash harness bulkhead connector (separate the fuse block from the bulkhead connector) You should see letters marking the rows and columns. The rows are A,B,C and D. The columns are S,T,U and V for the forward lamp harness and W,X,Y and Z for the engine harness. The following instructions will refer to these coordinates.

Includes wire color, engine side connection and dash side connection

You also need to move wires in the cluster connector to change from lights to gauges.


FORWARD LAMP HARNESS BULK HEAD CONNECTOR

AS – No wire (Should be black wire for key warning buzzer. Your warning buzzer will be under dash,)
BS – Dark Green – temp sensor or temp switch / temp gauge or temp light – Move from CZ
CS –No change (Light Blue –LH dir signal)
DS –Black – J-block /amp gauge –Move from DX Forward lamp harness wire to be added. Gauge cluster harness only
AT –No change (Black grounds at horn button for horn relay)
BT –No wire
CT –No change (Dark Blue –RH dir signal)
DT –Black/dark Blue/White (looks like Black/White) –horn relay / amp gauge –Move from CX. Forward lamp harness wire to be added. Gauge cluster harness only.
AU –No change (Light Green -head light high beams)
BU –No change (Brown –running/marker lights)
CU –Brown/White –voltage regulator / ignition switch (The brown white wire from the ignition switch is a resistor wire, supplies power to the voltage regulator when key is on) -brown wire to GEN light (light harness only) –Move from BT.
DU –Tan –brake dist block / brake warning light –Move from BS
AV –No change (Tan –head light low beams)
DV –Red –Main power feed to dash –Move from WD

ENGINE HARNESS BULKHEAD CONNECTOR

AW –Purple –starter solenoid S terminal / Neutral safety switch –Move from AZ
DW –No wire
AX –No wire (would be TCS)
BX –No change (Pink to ignition switch / engine side has white/orange /purple to coil)
CX –No wire
DX –No wire
AY –No Change (brown –coil / tach) Engine side wire to be added. Gauge cluster only.
BY –No Change (dark blue oil pressure switch / oil warning light)
CY –Yellow –power to wiper motor / wiper fuse –Move from DS
DY –Light Blue –wiper motor (washer pump) / wiper switch –Move from DT
AZ –No wire
BZ –No change (orange blower motor / blower switch) Used on heat only cars, not used on A/C cars.
CZ –Dark Blue –wiper motor / wiper switch –Move from CU
DZ –Black –wiper motor / wiper switch –Move from DU

Note: The wire in AY is found in a gauge dash harness only it is for the tach to coil. For a 70/71 harness this wire is not routed through the bulkhead connector. It is routed through a hole in the firewall.
Wires in DS and DT are for the AMP gauge, also gauge harness only wires. You will need to add these wires from the cluster connector to the connections under the hood.

Hey i just rewired the dash harness from a 70 Idiot light column shift diagram. Nothing works, it is dead in the water. Well maybe this procedure you have given me will correct it. Is a column shift diagram different from a floor shift diagram? Thanks alot, i got some work to do!

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The only difference between auto and man trans is the start safety switch. It is on the column on an auto trans car (neutral/park safety switch), or it's attached to the clutch linkage on a man trans car. The dash harness is the same for both, a short two wire extension harness is used for the clutch safety switch.

ok i got bad news. The car starts and runs now, but the guages still dont work. the lights in the dash come on except for the tach lights. Do i have a loose connection? I mean nothing works. The tach has a brown or tan wire from the cluster connector to the coil negative. Isnt that all it should have to work? I have an aftermarket MSD 6A ignition, is that causing the problems? I just dont get it. I am starting to get mad. Elree, the procedure was alot of help, but it didnt work completly. Maybe there is something in the forward lamp harness messing it all up.


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Oh yeah, i meant what is the difference, if any at all, between an automatic console shift and an automatic column shift. Thanks elree

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Did you rewire the cluster connector?

The console for the auto trans has the neutral safety and backup switch on the floor shifter. You need a console extension harness, a console harness and the shifter mounted switch.

Not all dash harnesses are wired with the console light connector. gray, orange and white wires in a three prong connector.

Elree, i have all the harness and the switch for the console. The dash harness is wired for the console, it all came from the same car. Can you beleive i bought a complete bucket seat interior, dash, console, seats and everything for 450 bucks? Beleive it. I will figure this thing out if it kills me.

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oh, i just thought of something. The car the dash and harness came out of had a 400 small block. Would that make any difference? I dont think so but the only dumb question is the one you dont ask, right? Later.


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ok, i think i got it all figured out except for a few wires. What wires go into the coordinates CU on the fuse bulkhead. I have two prodcedures that tell me different things. One says:"Brown/White-voltage regulator / ignition switch (The brown/white wire from the ignition switch is a resistor wire, supplies power to the voltage regulator when key is on)- brown wire to GEN light(light harness only) - move from BT." What does all that mean? And the brown wire coming from the fisher body connector, where does that go? The instructions from the conversion kit i bought from Muslce Factory tells me: "Splice with brown on ignition block", that is a 52" brown/black wire. I dont have a brown/black wire. I also had a black with pink striped wire, where does that go?

The 72 light harness has a brown/white resistor wire and a brown wire that are in the BT location. The brown/white wire is from the ignition switch, the brown wire is from the GEN light. On the 70 harness these wires are in the CU location. So you need to move them from BT to CU. When conversion to a gauge dash the brown wire from the GEN light is not used and can be clipped at the bulkhead.

The brown wire in the fisher body harness, also called the intermediate harness, is for the tail lights and license plate light. I don't know why the instructions want you to connect to it. I don't know why you need to do anything with it except plug the body harness into the dash harness.

I also don't know what 52" brown/black wire the instructions is referring to. Without reading the entire instructions it's impossible to comment on them. The information I have provided is for factory gauges.

Thanks Elree. Any comments on the black/pink wire?


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Anything "pink" is a switched ignition line.

The only black/pink wire I know of is for the TCS circuit. Are you refering to a wire in the engine harness or dash harness. I'm just guessing but I think it's on the old 70 dash harness.

The black wire with the pink stripe is in the dash harness. It comes from a connector near the climate controls. It is spliced with a brown wire that is also in the same connector. What i mean is not a two terminal connector, a single terminal connector that plugs into a switch on the climate controls. I beleive this switch turns the A/C off. Where in the fuse box does the black/pink wire go? Does it splice with another wire already in a coordinate location? Thanks.

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The wire you are talking about, is it on the 72 harness that you are installing or the 70 harness that you removed from the car?

A black/pink wire attached to the A/C power feed wire is typical of a 70 with A/C harness. If you look at the fuse block the top right fuse is marked A/C TCS. The black/pink wire is power to the TCS I think location AX. The 72 harness handles the TCS circuit totally different. The TCS relay in in the dash harness as opposed to being under the hood as on 70.

If I remember correctly the 72 harness doesn't have a black/pink wire. I will check when I get home tonight.

This might help alittle. I have an old 70 malibu sweep style dash harness. I found the black/pink wire spliced with the brown wire. I traced the black/pink wire to location AX in the fuse box. And the brown wire went to a fuse that was labeled A/C TCS SOL.

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This is a 72 harness and it has a black/pink wire

Well I checked several 72 harnesses and none have a black/pink wire. All I can say is if it connects to the brown wire that powers the A/C controls then it will be for the TCS and will go in the AX location. If you are going to use the TCS then you will need power to it. If you don't use the TCS I recommend you not connect this wire. It is fed through a 25 amp fuse I have seen more several of these wires with melted insulation. A short under the hood melts the insulation on the wire under the dash before blowing the fuse. 71 and 72 powers the TCS via the radio fuse, a 10 amp fuse. Hope this helps.

Thanks Elree thats does help. I figured out why my tach didnt work. I have a MSD 6A ignition, and the wire to the tach hooks up at the MSD box, not at the coil negative. Well i figured that out but it still doesnt work, turns out that i need an adapter. At least the MSD intallation instructions says i do. My temp gauge still doesn't work. There is a resistor on the back of the Idiot light fuel gauge that is supposed to go to the new temp gauge. The conversion instructions say to mount it vertically. Is that a typo? Shouldnt it be mounted horizontaly? the pbs(printed circuit board) leads to the horizontal terminals on the temp gauge. To me it makes sense to mount it horizontaly. Amp gauge now works. Fuel gauge now works. All i need for the tach is that adapter. And all i have to figure out is the dang temp gauge. Thanks for your help. Got anything on the temp gauge?

Ray

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The resistor does install between the vertical terminals. The bottom terminal needs to make contact with the cluster metal back which is grounded. Grounding the green wire at the sender will cause the gauge to go full scale the same will happen when cranking the engine, the green wire also connects to the ignition switch and grounds when the ignition switch is in the start position.

Wow,i never would have thought of that. That got it working. I would be lost if it wasnt for this website and you man. Now all i got to do is get the tach working. I installed the wire from the tach output on the MSD box. It still didnt work. I read further in the MSD manual and found that i might need an adapter. Do you think i need this, or is there a problem with my tach. Remember it is a brand new tach from Muscle Factory. The line is connected straight from the MSD box, to the tach. There is no in-line filter here. Thanks

Ray
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The tach should work with the MSD 6 ignition. Make sure it has power and ground. You can also visit http://www.msdignition.com/ their web site for information.

Hey, i called tech support at MSD. They told me to check the tach output on the box. It should be about 1-5 volts. Over 5 and it is bad. I borrowed a volt meter and it read about 2-3. If it is good than the tech guy said i need an adapter. Well everything is working now. I must thank you for your generous help. If you ever need anything, you know my email Ray70ss@aol.com. Thanks again


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