Yes there are different alternators fitted to the MK1’s and Mk2.5. They look similar, but the MK1 alternator regulates itself and the MK2.5 alternator is controlled by the ECU.
If you have a fully charged battery, you could try disconnecting the wires on the back of the alternator, put some themporary insulating tape around them and then make sure they are not fouling the belt.
If you start the car, the only light that should be on is the battery charging light, if when you rev it, the other lights are out. I suspect you have the wrong alternator.
If they are still doing the same you have another problem
Is it a brand new or used alternator? I’ve seen that concern in the past with ageing alternators. I put it down to the brushes not being able to maintain contact with the slip rings in the alternator at higher revs.
Can you let us know any make/part numbers on the alternator Jeff.
Robbie’s suggestion, if it is a used alternator is likely correct. The original Hitachi LR180 alternators fitted to these cars have two brushes, one mounted above the other that run on slip rings. The bottom brush wears the ring and brush quicker than the one above for some reason. There is the distinct possibility that the brush has worn to the point that there is not enough contact in some circumstances or that the increased pressure on the braided connector wire has damaged it to some extent.
Would be interested to know what the battery voltage is when car running and alternator charging battery at idle.
I agree with MX5123 - and the OP thinks he’s got the wrong alternator. With the alternator connected, at high revs the volatge across the battery should be not more than 14.5 volt, but a wrong alternator will exceed that, - E.G. higher than 15 volts. This needs two to check, one revving the accelerator and the other checking the voltage across the battery. Wrong alternator is a common mistake, and will also give rise to the symptoms listed. Suppliers often do this. (past history)
I have looked at Europarts listing for that part and looks the correct 80 amp alternator that would suit MK2 and MK2.5 cars. I hope you got some money off that listing price?
The voltage reading you are now getting look fine. 15.01 volts is a little high but allowing for this, some multimeter innacuracy, extra battery charging(lowish latent voltage) and that is probably absolutely correct.
Had a customer who returned an alternator. I found two insulating seals in the two pin alternator socket. There should be only one on the loom plug so 2 in the wrong place would have prevented proper connection and caused issue. Removed seals and fitted to another car myself - worked fine. The plug should clip reassuringly in place.
Been for a test drive and no radio resetting or random dash board lights.
I think the route cause was the plug on the side of the alternator not being clicked into place by me.
So it fixed itself be doing the first test to run on the battery alone.
Thanks to rhino666, mex125, RoadsterRobbie, RymondHarper and Gerryn for help and suggestions.
Jeff.
TIPs for others.
Make sure the plug on the alternator clicks back into place when re assembling.
Removing the plastic duct from the air filter to the engine and the radiator fan will give access to the alternator and power steering bolts from the top. No need to remove the stone guard for bottom access to alternator bolt.
You will have to remove a manifold bracket to remove alternator mounting bolt. 3 x 14mm Bolts.
Check and double check you have been given the correct belts from the parts supplier. 4PK860 is not the same size as 4PK860 Elast.
For correct tension the drive belts should just be able to just turn 90 degrees and no more.
Disconnect battery before working on Alternator.
If its an exchange Alternator take the old one with you and get your money back on the spot.
Buy a new LED inspection Lamp. I blew three old fashioned bulbs on my old inspection lamp. Well worth it.
Grease bolts when you put them back in case you have to take it all out again !!
P.S I paid £123.41 instead of £186.99 inc vat for part.
The symptoms are that at about 3.5K revs I would get random lights come on on the dash board and the radio would cut out.
I did notice that when parked up with the hand brake light on it got suddenly brighter around 3.5K revs just before weird thinks started to happen. Nothing to do with handbrake but it was a light I could study while revving the engine.
In the end I took back the Eurocar Parts alternator p/n 401680952 (RTX Alternator) and exchanged it for a branded Lucas LRA02925.
