TR idling rough won't accelerate pass idle

You need to check the function of the Protection Relay in the Black Box over the RR wheel well -- it's what supplies the +12V you are missing.

(The radiator fan not working needs to be fixed, but it has no relationship to the Protection Relay function.)

 

Yes, that's always possible as just getting into that box requires you to unplug and reseat the round C12 and C13 connectors (so that can "fix" a bad connection in those), and everything, generally, gets a good wiggle

 

You need to determine if the protection relay is bad or if some of the input signals to the protection relay are missing. Do these three test:

#1. Is the 10A fuse OK?

#2. Measure the voltage between terminal 30 and terminal 31 = this should always be +12V.

#3. Measure the voltage between terminal 15 and terminal 31 -= this should be +12V whenever the engine is cranking or running (it might droop down to ~10V when the starter motor is cranking, but it shouldn't be 0.2V).

If you pass those three tests, but you do not have +12V between terminal 87 and terminal 31 = buy a new protection relay.

If you don't pass those three tests (do not buy a new protection relay yet), give a shout back and we'll look at getting whatever is missing fixed.
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The ZB (purple-white) wire leaves the fuse-relay panel thru the j horizontal white connector at the bottom of the fuse-relay panel and passes thru the small round C13 connector on its way to terminal 15 of the protection relay -- try measuring at those locations to ground during engine cranking or (barely) running. That same ZB wire signal closes the fuel pump relays, so since you report the engine will run, the signal must be present at the fuse-relay panel and must be lost either at the j or C13 connector.

 

Sounds like the protection relay is defective. You can remove the relay from the socket and jump the 30 and 87 connections (preferably with a fused jumper). The engine should start and run fine.

 

This is normal. Terminal 87 is driving a load (so it does look like a ground to a voltmeter when it isn't connected to terminal 30).

The "jumping" is a bit dangerous as this disables the over-voltage "protection" function (with or without a fuse).

If you've got something actually loose inside the protection relay that wouldn't be good, but, if you shake it vigorously, the contact arm could be moving and making some noise. I'd go back to square one -- with the protection relay in place what results do you get for those prior tests (30 to 31, 15 to 31, 87 to 31)?

 

This is an indication that you have a high unwanted resistance somewhere in the GR (yellow-red) wire path from where the loop terminal with the GR wire starts out at the +12V battery cable at the starter over to terminal 30 at the protection relay (and explains why "jumping" didn't work). I don't have the TR schematic with me, but the most likely suspect is where the GR wire passes thru either the C12 or C13 round connector. Make the same measurement there (i.e., between the GR wire and ground with the engine running on both sides of the C12 or C13 connector) -- if both sides are 0V, then have a look at the GR wire loop terminal at the starter +12V battery cable. Bottom line is that you have to have +12V present on terminal 30 when the engine is running.

 

The GR wire goes through the C12 connector, the larger of the 2. The rotating lock ring on those is fragile and the tabs that actually hold the plug in place break off. Once that happens poor or intermittent connections are the result. Later cars like yours have the semi flexible conduit to that plug and almost invariably apply some angular force insuring a poor connection to some or all of the wires going through that plug.

I have seen all nature of jury rigging to hold them in place but best to replace it. They are available. It is a standard AMP part and not very expensive.

 

The voltage measurement has no meaning when not under load (i.e., with the protection relay removed).

Having low resistance in those two paths is a good thing, but what you are not measuring is the contact resistance between the two GR pins in the C12 connector. If you remove the protection relay what is the measured resistance from large +12V stud on the starter with the GR loop terminal (place the multimeter probe on the threaded stud itself, not the GR loop terminal) and the female terminal 30 in the protection relay socket?

 

How was the white connector for the fuel pumps. Also what did you spray the connectors with?

R

 

Can't say that that is "bad" result - but it should be working

It's not physically possible for the protection relay to "short" the voltage down that much - a starter draws ~200A and causes the battery voltage to droop down to 9~10V. A short causing an auto battery to go to near zero volts would be thousands of amperes -- which would vaporize the protection relay itself from the heating.

 

When you are measuring the voltage at the relay socket with no relay in place, there is no load on the circuit, which is why you are seeing 12v. When you jump the relay, you are placing a load on the circuit, and the supply voltage is dropping to almost zero, because there is excessive resistance upstream of the relay socket in the Yellow-red wire, most likely at the large round AMP connector.

You could use a different load, such as a headlight to check power at pin 30 on the relay connector to simulate something that actually draws current, as your voltmeter does not draw any current.

Or you could run a jumper wire directly from the starter power terminal to the backside of the pin 30 on the protection relay and then plug the relay and see if the car runs normally. This way you are bypassing the bad connection in the yellow-red wire and testing the protection relay at the same time.

I would normally perform a voltage drop test across the connection from the starter ter. 30 to the relay ter. 30 with the relay in place and the engine running. It should be less than 1v, if it is more, then you have excessive resistance in that part of the circuit (most likely the large AMP connector)

 

You are not checking the connection under load. Using an ohmmeter places no load on the circuit. That is why you should perform a voltage drop test across the same terminals with the circuit under load.