pinstripebob Posted June 17, 2018 Share Posted June 17, 2018 Hi guys, I'm working on a 1971 Monte Carlo's electrical system. This car is a bit of a mystery, it's a 1971 body with a 1972 front end, a 1977 engine (with HEI distributor), and a very hacked up wiring harness in the engine bay. I have a 1970 parts car that I snagged the wiring harness off of. I have a 1971 wiring diagram, but I'm struggling with the connector at the firewall. No wiring diagram that I have seen matches the pinout of either wiring harness, and no wiring diagram matches the pins at the firewall on either car. I've attached a photo of my fuse block connector at the firewall so you all can see what pins I'm working with. No diagram matches this pattern. Can anyone help out, maybe with alternate wiring diagrams? Are there any tricks I can use to figure out which pin should go to what part in the engine bay? Any help is appreciated! Thank you! Quote Link to comment Share on other sites More sharing options...
pinstripebob Posted June 17, 2018 Author Share Posted June 17, 2018 I should also note that I'm able to remove and replace the pins in the connector as needed. If I can get a solid diagram showing what wires should go in what spot in the connector, I'm good to go. Quote Link to comment Share on other sites More sharing options...
LS5 Posted June 17, 2018 Share Posted June 17, 2018 Garrett, looking at your plug the left side will be the engine harness side and the right side is the forward harness such as headlights etc... The side you need to be concerned with is the inside by the brake pedal. thats the color codes you need to follow. Our wiring harnesses are specific per year. 1970 wont work in a 71 unless you choose to adapt a lot of the wiring and move the pins as you mentioned. if you can trade that harness for a 71 that would be better and also the harness's are different between a Tach and Gauge harness and an Idiot light harness. the dash harness and underhood harness Must match as you Cant mix them such as a Dash tach and gauge harness and then an idiot light front harness. if you find a Service Manual for 1971 chevelle/ monte carlo that will have the diagrams in there you seek. Darren Quote Link to comment Share on other sites More sharing options...
Paul Bell Posted June 17, 2018 Share Posted June 17, 2018 The dash and interior wiring for 70 through 72 is the same. Under hood, the 70 harness is alone, 71 & 72 are the same. Having said this, the wiper/washer switch and seat belt warning stuff is unique to the 1972 car but not noted in the factory wiring diagrams. Quote Link to comment Share on other sites More sharing options...
pinstripebob Posted June 27, 2018 Author Share Posted June 27, 2018 Following up on this, I have the wiring diagram for a 1971 and 1970. Both of them show some differences between the 2 harnesses I have, mainly where pins are located. Thanks for the diagrams Paul! Here is what I have to be clear: Damaged 1971 harness, with tachometer Good 1970 harness, without tachometer I've moved most of the pins, in fact I've confirmed that the body harness is correct and complete now. I'm running into some trouble with the engine harness, of the 14 slots for pins I have 4 of them confirmed. Is there a wiring diagram that is specific to the 1971 tachometer and another specific to the 1971 non-tachometer that I could get my hands on? So far everything seems to be non-tachometer that I can tell. Quote Link to comment Share on other sites More sharing options...
RealRed70 Posted June 27, 2018 Share Posted June 27, 2018 Are you trying to use the good 70 non tach dash wire harness? Are you trying to convert the non tach 70 dash harness to a 71 tach dash harness? Are your engine bay harnesses original for a 71? The dash wiring for 70 through 72 is NOT the same. Under the hood 71 and 72 are NOT the same. 1 Quote Link to comment Share on other sites More sharing options...
RealRed70 Posted June 28, 2018 Share Posted June 28, 2018 What is damaged on your 71 tach dash harness? Quote Link to comment Share on other sites More sharing options...
RealRed70 Posted June 28, 2018 Share Posted June 28, 2018 The location of the wires in the 12 pin connector for the instrument clusters for 70-72 are the same, but the firewall end of the harness is not the same. The wires are in different locations on that end of the harness. Quote Link to comment Share on other sites More sharing options...
pinstripebob Posted July 21, 2018 Author Share Posted July 21, 2018 Hi Red, Sorry for the delayed response, life has continued to be busy and kept me out of the garage. I am working under the hood only. My 1971 harness at the firewall was cut up badly by a previous owner. The main plug is split into two plugs, one that controls all the lights and similar items and one that powers the starter/ignition/etc. The harness that controls lights and such is now in good shape, confirmed with a multimeter between the under hood plug and fuse panel in the cabin. The other half is not fixed yet. I have a donor non-tach 1970 car and harness, the vehicle I'm working on is a tach 1971 Monte. My struggle is looking at any diagrams I've found on the Internet, including those in this thread, wire colors do not match the pin out shown when compared to either harness I have. For example, the half connector with two extra "legs" that wrap around the other half, pin WA in the corner on the tach 71 is black, but on the non-tach 70 is thick purple. No diagram I have found matches either of this pin. Any thoughts on that would be great! I'm wondering if there are other diagrams for other options I haven't found yet? Quote Link to comment Share on other sites More sharing options...
pinstripebob Posted July 21, 2018 Author Share Posted July 21, 2018 Hi Red, Sorry for the delayed response, life has continued to be busy and kept me out of the garage. I am working under the hood only. My 1971 harness at the firewall was cut up badly by a previous owner. The main plug is split into two plugs, one that controls all the lights and similar items and one that powers the starter/ignition/etc. The harness that controls lights and such is now in good shape, confirmed with a multimeter between the under hood plug and fuse panel in the cabin. The other half is not fixed yet. I have a donor non-tach 1970 car and harness, the vehicle I'm working on is a tach 1971 Monte. My struggle is looking at any diagrams I've found on the Internet, including those in this thread, wire colors do not match the pin out shown when compared to either harness I have. For example, the half connector with two extra "legs" that wrap around the other half, pin WA in the corner on the tach 71 is black, but on the non-tach 70 is thick purple. No diagram I have found matches either of this pin. Any thoughts on that would be great! I'm wondering if there are other diagrams for other options I haven't found yet? Quote Link to comment Share on other sites More sharing options...
pinstripebob Posted July 21, 2018 Author Share Posted July 21, 2018 Another thought, a physical 71 tach diagram I have shows a 6 cylinder and this is a V8 car. Quote Link to comment Share on other sites More sharing options...
pinstripebob Posted July 21, 2018 Author Share Posted July 21, 2018 Another thought, a physical 71 tach diagram I have shows a 6 cylinder and this is a V8 car. 1 Quote Link to comment Share on other sites More sharing options...
stangeba Posted July 22, 2018 Share Posted July 22, 2018 I downloaded these many years ago and don't know anything about them. Good Luck! This is something about HEI. Quote Link to comment Share on other sites More sharing options...
pinstripebob Posted July 26, 2018 Author Share Posted July 26, 2018 Awesome! Looks like that helps out with the ignition coil wire! Quote Link to comment Share on other sites More sharing options...
1970mcss Posted July 27, 2018 Share Posted July 27, 2018 The thick (12ga) purple wire on my 70 goes to the starter solenoid if that helps Quote Link to comment Share on other sites More sharing options...
RealRed70 Posted July 27, 2018 Share Posted July 27, 2018 It is really hard to help you when we really do not know what you have going on there. Quote Link to comment Share on other sites More sharing options...
pinstripebob Posted August 17, 2018 Author Share Posted August 17, 2018 Thanks 1970mcss! I had that traced, but it's good to get a confirmation! RealRed70, hopefully I can try clearing up what I have and what I'm doing. Also I'm not sure why some of my posts repeated themselves. What I have: 1. 1971 Monte Carlo, tachometer car, with damaged engine wiring harness (larger connector shown in post #13 above, second document) 1a. Engine wiring harness had all wires cut or cut & spliced except the tachometer feed wire, repairs are starting nearly from scratch. 2. 1970 Monte Carlo, non-tachometer car, using as a parts car with intact engine wiring harness 3. 1970 Chevelle, El Camino & Monte Carlo GM Restoration Parts Assembly Manual. 3a. When purchased, 1971 was not available and there was no knowledge that the two years have wiring discrepancies. Current status: 1. 1971 forward lamp harness is correct, verified most wires with multi-meter 2. 1971 engine harness has 6 wires confirmed, there are 14 total pins in this connector leaving 8 positions that need to be confirmed. The second document in post #13 above from stangeba shows how the engine harness connector is labeled for each position (e.g. WA, YC, ZB, etc.). I have ZA, YA, ZB, YB, YC, and YD mapped and verified. What I have noticed is the wiring diagrams I have found so far do not 100% match my forward lamp harness or engine harness in my 1971 Monte Carlo. If I could find a diagram that showed the connector such as post #13 above with exactly what wire goes in each connector position, that would be perfect! Good photos showing wire size/color and where it goes in the connector would help also. 1 Quote Link to comment Share on other sites More sharing options...
Dans '70 Z20 Posted September 4, 2018 Share Posted September 4, 2018 FYI if needed. Wiring harness are available complete from here. Ordered my front harness from them. Perfect in regards to color, lengths, connections, clips etc. M & H Electric. http://www.wiringharness.com Dan Quote Link to comment Share on other sites More sharing options...
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