Just purchased 91 TR. Runs fine, but the slow down (high temp) lights don't illuminate when the key is turned (the brake light does, though). My service manual doesn't even have the lights, wiring, ECU's etc. listed! I noticed the sensors and ECU's were disconnected, so I clipped them all together, but still no luck. Do I need this "feature"? What should I check next? Are there any updates to the service manual that might be useful? Any guidance would be very much appreciated!
The OM for your year/version TR is the best available source of information on the slowdown warning light system (and it's not much). IMO, if you've got cats on the car, you at least have to make an attempt at having a working overheat warning system (if no cats -- no need for a temp detecting system). TRs are about the last F model where a slowdown warning light system indication (even a false one) doesn't shutdown the injection system -- so the engine will run whether you get a false indication, or fail the self-test as you are now, or unplug everything as you were. Passing the self-test gives some assurance that the system might work , but failing the self-test is game-over. You really have the more dangerous failure -- where it's just totally dead. A system giving false positive indications gets fixed because it's damn annoying, but a dead system can go unnoticed (kudos to you for knowing there was a self-test to be observed). Thermocouples are very rugged devices so most likely the warning light ECUs, but please make your own checks -- both items are pricey and there is wiring + fuses involved. If you want to confirm that the +12V power is present or not to run the warning light ECUs, measure the voltage between the green/white wire and the black wire (ground) in each of the unplugged warning light ECU connectors with the key "on" -- should be +12V.
Thanks very much for the help. I checked the connectors, and there is 12v going to each of the ECU's. Is there any way to test the system to determine if the ECU or the bulb is at fault? I assume the sensors are irrelevant at this stage of the game, since I would expect the lights to go on even if they were disconnected. Since the connector has 3 wires, does the third one go to the bulb, and if so, would shorting that terminal to the green/white (+12v) light the bulb? By the way, my Countach has a much simpler system: the catalysts glow red when the temp is too high!!! Needless to say, no more cats...
The way it works is +12V is always on one side of the filament (key "on"). When the warning light ECU "grounds" the other side of the filament, the lamp goes "on". (The +12V at the ECU is just used to run the ECU itself.) Jumper the green wire (this is the other side of the filament) to the black (ground) at one connector and the red wire (also the other side of filament) to the black (ground) at the other connector -- it should light up the corresponding lamp (I can't recall offhand who's red and who's green). If this works (which is very probable IMO, and the thermocouples have continuity), you can buy new warning light ECUs with very little chance of regret, some pain, but no regret
Thank you for the reply. Good thing I did it your way, and not mine! Following your instructions, both bulbs are OK, so the ECU's must be at fault. The dealer wants $700 per ECU, so I guess I'll shop around (maybe get it down to $690). Thanks again; you've been a great help...
Many of us have needed to replace those units so I'm not surprised that you wound up joining the club. IIRC, I paid in the mid~high $300s each, but that was about three years ago -- give Sponsor RicambiAmerica a chance to quote a price too.
