View Full Version : O/D and dash wiring

06-03-2011, 08:08 PM
Got no switch, just three wires coming up from the tunnel. Who goes to what? Rest of the dash wires are unplugged and nothing on the dash work save the temp gauge. Where can I get a good diagram and/or manual? Thanks.

'76 6

Andrew Mace
06-03-2011, 09:18 PM
Here's a very good wiring diagram (https://www.advanceautowire.com/tr2506.pdf) from Advance Auto Wire; OD stuff is down towards the lower right.

Notwithstanding any other wiring issues in or near your dash, the OD could be a column switch...or a slide switch on the gear knob, depending on the origin and installation of the OD gearbox.

06-04-2011, 09:23 AM
The Bentley Manuals have a really good diagram showing dash guage and wiring layout from the service position.

06-04-2011, 09:58 AM
Probably two of those three wires are for the reverse lights. If you can't read the colors (or the wires have been replaced), some quick detective work with an ohmmeter (or the ohms function of a DMM) should identify them:

With the transmission in neutral, measure the resistance of each wire to ground. All 3 should show open. Now shift into 4th gear and measure each wire again. The wire that was open before and now shows somewhere around 10-15 ohms goes to the overdrive switch.

06-04-2011, 10:02 AM
Original wires and the colors are hard to see. I ran it on the lift in 4th and just jumped it out directly to the noid just to see if it was working. I got it to go in once or twice. really weak spark when connecting. I think the ground may need some help as it feels loose and is covered in oil.

Thanks guys!

I'll have lots more wiring questions in the future. The dash wiring is a mess.

06-04-2011, 10:10 AM
I think the ground may need some help as it feels loose and is covered in oil.
Quite possible, I had that problem with one of the Stags. Only a little bit loose, wouldn't pull off easily; but that little bit of play was enough to make the OD not work sometimes. Pulled the terminal off, crushed it just a bit with a pair of pliers and put it back.

06-06-2011, 09:38 AM
you might need to take those switches apart and clean the insides. My reverse lights didnt work when I got my TR6 and turned out that the switch was stuck in the ON position or Closed as the electrical guys would say


06-07-2011, 11:21 AM
There is an eBay seller that has great large format wiring diagrams that are laminated for cheap. Highly recommended!

06-07-2011, 11:41 AM
Tom, just have him copy Dan's to a thumb drive ,take it to kinkos and have them blow it up to 36X25 if he wants